L24 build questions

[rayaapp2]

try not to poke fun of the bungee tied BMW battery. This car doesnt really get driven ever.

 

Im building this L24 out of my 71 240z. Its the original L24 and its in pretty good shape. Id like to see what I can do to pull more power out of it. It just lacks mid range and top end. Id be happy just to get some mid range at this point.

 

So far here is what I have:

E31 head with stock ports, 2 cracks in the combustion chambers have been repaired. I had the machine shop also replace the valve guides and seats. While I had the seats out I went with the slightly bigger new L28 N42 head valves. The seats and guides are now up to current oil specification not the old stuff that needs the additives(not like anyone uses the additives or even notices excessive wear without it in these). I used Schneider valve springs with those new seats. Other than that its pretty much a stock E31 head.

 

The Cam is currently a "C" cam with external oil bar. I used the matching lash pads and checked the wipe pattern. I suspect the cam lobs are worn down, but I dont have cam card to verify at this point if Im missing any meat from the lobes. There just isnt any mid or top end power. My butt says the engine runs out of poop around 2500 rpms. But my butt isnt a dyno so ? I have another "A" cam, but I think that its time for a re-grind and to stop messing around with old used cams for a good build. I will probably call a re-grind company as certain members have said time and time again and see what the cam engineer says. I have done a little research, but Im not set yet. These guys look promising: Web Cam Inc. 1815 Massachusetts Avenue Riverside, CA 92507-2616 USA webcamshafts.com. I have been looking at their 91 and 94a cams. They regrind or sell CWC that is nitride hardened. I have a few old "japan" cores so Im not going new. But maybe you guys know of them and can tell me what the deal is with them verses others?

 

I used a header that a Datsun Dealer installed. It has long small tubes that dump into 2 2" collectors about midway down the stock "A" 4spd transmission that I now have routed to a MSA twice pipes system. Its one of the longest headers Ive seen and the originally the secondaries "Y" together at the inlet to the original pre-muffler in the center of the car. So its dual exhaust as of now. I suspect that placing a small tube somewhere in between the 2 exhausts will help with scavenging, but I have no clue where to do it without a dyno a lot of cutting and welding to get it right... not to mention tube size options. As far as the MSA exhaust parts, Id take a guess that the pipes are to big for my poor little L24 and that I should probably be a little worried about reversion currently. They are better than the plugged up stock exhaust that was still on there though.

 

The induction system is currently stock SU carbs. My plan is to run a set of Mikuni carbs on a Mikuni manifold. Im still debating on 40s vs 44s. If I had a flow bench the guess work would have been eliminated as I know how to do all the math to figure out carb size for any engine. I could most definitely use any help here. Im guessing that 40s would be more than enough for a streetable L24, but I have read multiple times that people prefer 44's. Im half tempted to use a dial-a-jet on the stock SU's, but the main jet and needle are extremely limited for any big numbers as it would always be ultra lean at WOT.

 

Im using a pertronix ignition unit currently. Im using NGK split fire plugs 1 step colder than stock. Nothing special. I started playing with the mechanical advance on the stock L24 distributor. This is new ground for me and I dont fully understand the basics of timing here. The stock timing curve on this engine just seems inadequate for the high reving "L-Gata"(got this fixed!). So I pulled the whole assembly apart just to see what was going on in there and try to understand how it works together. I do know how the weights, springs, and assembly work in theory(thats pretty basic). I noticed that the shaft that the rotor sits on moved very little. I pulled it off and saw that there are 2 different springs in there on the weights. The upper shaft(one with the rotor) has slots that the weights fit into as detents. The way it was in there before did not allow a lot of movement. So I put it back on 180 off and gained a little more movement. It looks like if I wanted to get crazy with it I could dremel those detent notches out to get more advance(obviously the springs would have to match this change right?). Whats the deal with the 2 different springs and detent notches? I mean why dynamic and how does that affect the timing curve. The sbc's Ive played with usually have the same springs on both weights. Where can I go to figure out how to choose advancing springs? I mean how can I determine how much advance I want for the cam/engine combo? There's that and there is total mechanical advance that is being limited by the the detent slots on the upper "rotor" shaft that I need to figure out. OR should I be looking for a distributor that is already capable of more total mechanical advance. I actually read a couple of posts already on hybridz and zcar about L24's and timing advance. Unfortunately there was nothing on the basics.

 

The head gasket is a HKS MLS 1mm gasket.

 

I have an 81 turbo oil cooler that I plan on mounting to the engine as well.

 

My plans for the bottom end are as such: I believe the valves need to be unshrouded in the current setup. I was thinking 85-86mm bore would help that. How will the extra large bore affect the rest of the bottom end. I know there is an optimal stroke:bore, but I have no clue how to figure that out. Is there a point in which it would be best to go with the L26/L28 crank and rods to keep a well balanced engine. Id like to up the compression to 9.5:1 at least! If I could get fueling dialed in I wouldnt mind going a little bit higher. My goal is to not use anything higher than 91 octane fuel though. After seeing what stock SU's on the L24 preform I know why high compression is a BIG no-no with these L-series. WOT optimally in my opinion should be close to 12.5:1 afr NOT 16.8:1 with idle sitting at 10:1 afr(found my data: ASM test 15mph/50% load @ 15.43:1, 25mph/25% load @ 16.07:1, and idle @ 11.08:1 was the best I could get it. My starting numbers were closer to 18:1 at 25% load with driveway tune). But thats just my limited experience so far with my L24. While Im working on the bottom end Ill make sure to replace the bearings and check all the journals. I will be looking around for a set of the rods with bigger rod bolts. Ive had at least 3 L series 6 cylinders lose rods and have it been related to the rod bolts. Lesson learned. Buy NEW rod bolts and use the big ones. I have an 81 turbo oil pump to work with as well. I have spoke with JeffP about that in the past. I have no plans for the oil pan. I have 2 good machinists in Sacramento to choose from. Im going to have the rotating assembly balanced out.

 

I know thats a big list with lots of questions. Hopefully its something you guys can properly critique me on at least.

 

I have fired these questions off to others via email as well.

 

Thanks guys and I look forward to reading your input.

Edited December 5, 2010 by rayaapp2

[johnc]

Your problem is most likely ignition related. Here are a couple old posts from the Internet Z Car Club that I archived:

 

The following is the a distilled version of the Frequently Asked Questions and discussions (FAQ) about

 

Z car Ignition

 

as discussed on the Internet Z car club.

 

[The Internet Z car club is an international mailing list with over 125 members and transmitted to a member's computer account over the internet.]

 

All information published here is the property of the original authors who are members of the IZCC and may not be reproduced for commercial purposes. Everything stated here is based on the experiences and opinions of the original authors. The authors and editor accept no responsibility for any damages arising from use of this information. Always consult your workshop manual and take appropriate precautions when working on the car. If in doubt consult a specialist.

 

Q:What ignition upgrades are possible for the Z ? Are the late model (260 and up) electronic ignitions adaptable to the 240Z ?

 

A: There are a few possibilities for upgrading the Z car ignition. The 240Z, with stock point-type ignition, are the most likely targets. Point-type ignition is old technology, and has several shortcomings for performance applications, like low spark voltage, point bounce at high RPM, and high maintenance requirements due to the mechanical nature of the system. The following sections detail some of the more popular ignition upgrades.

 

* USING AN ALLISON ELECTRONIC IGNITION:

 

The Allison Electronic Ignition, available from several sources, will upgrade the point-type 240 ignition system to an electronic-type. The kit consists of a set of optical "points", or pickup-set, which mounts in the distributor instead of the mechanical point set, and the electronic control module. Installation is pretty straight forward, and requires no modifications past the installation of the aforementioned items. Allison also offers just the control modules for 260-280 applications which already have a non-point type distributor.

 

Because the system is optical-based, as opposed to magnetically-based, it can be susceptible to dirt which will hinder operation. When operating properly, the system provides much improved starting and overall performance due to the more precise timing provided.

 

* USING MULTI-SPARK DISCHARGE (MSD) SYSTEMS:

 

The MSD (Multi-Spark Discharge) system is an electronic ignition system that discharges a series of sparks in a continuos discharge over several degrees of crank rotation. This technique provides vastly better ignition especially under marginal conditions. It makes a big difference in idle quality and low speed running. It will trigger from either points or variable reluctor pickups. The MSD-6AL contains the rev limiter. The MSD-6T comes with a shock resistant mounting kit that makes mounting the box on the firewall next to the battery very easy. The rubber stand offs let the box straddle existing wiring.

 

The MSD box, like most aftermarket ignitions, replaces the stock system. It takes its trigger from whatever pickup is in the distributor and fires a coil. It wires somewhat different than stock because it has a high peak current draw. A power supply lead wires directly to the battery. A "gate" signal that turns the unit on is wired to the old ignition voltage source. New wiring is installed to the distributor and coil.

 

One modification that must be made with the MSD system is the tachometer hook up. You must use the "tacho" output of the MSD box which is like a logic type signal. This signal, however, is too low in amplitude to trigger the Z tacho. On the early tacho that was inductively coupled to the ignition lead (pre-75), simply remove the inductive loop from the tacho and run a wire from the tacho input to the "tacho" output of the MSD box. On 75 and latter systems, remove the tacho lead and run a new lead to the "tacho" output on the MSD box. Then disassemble the tacho and find the large power resistor that is in series with the tacho input. There are typically two resistors in series with this lead. One is physically large and the other is not. Short the larger resistor by placing a jumper around it. Reassemble the tacho, install it and away you go.

 

Be sure to use magnetic suppression wire and not resistor wire. The peak spark current with the MSD box is on the order of 1 amp and you'll lose a volt an ohm across resistive wires. If your wires are 5000 ohms, you'll dump 5000 volts just on the wire.

 

The following excerpt details the steps taken with an MSD installation. The Z car in question uses a Holley carby conversion:

 

I selected the MS-6T model which is a medium energy model designed for circle track, NASCAR and turbocharger applications. It is ruggedised and contains an interface connector for adding a soft rev limiter. It comes with rubber mounting bushings that isolate the unit from chassis vibration.

 

Before installing the unit, I connected it up on the electronics bench and instrumented it. The unit does its magic by discharging about 400 volts into the coil at about 3 khz (at low rpm) for each trigger pulse. The repetition frequency and the number of pulses varies with rpm. The shift from one rep rate to another is a discrete function; the unit "shifts gears" as rpm increases. On the bench, I used an ordinary coil for sparks and a pulse generator to trigger the unit. The first observation was that at high rpm, the unit delivers enough spark energy to melt the end of the paper clip I used to establish an arc gap. The next thing I noticed was that at high rpm equivalent, the input energy was way too much for the stock coil to handle. It rather quickly heated up and started oozing oil from around the top and started bulging a bit. The MSD unit, meanwhile became only warm to the touch. An ammeter on the supply showed that the unit drew a maximum continuous current of 9 amps at about 9000 rpm equivalent. This unit puts out some serious sparks! (as a whim, I connected the MSD coil output leads to a PA loudspeaker - You should have heard the noise! Surprise! the speaker survived.)

 

The unit is fairly large so finding a mounting place is a chore. I started to mount it under the seat but lazed out and mounted it on the firewall in a vertical configuration just to the right of the battery. The unit comes with rubber stand off feet that hold the unit up off the A/C vacuum hoses and wiring. It was necessary to remove the cowl (where the windshield wipers come out), bore a 1.5" hole in the heater inlet baffle and then bend another baffle slightly in order to apply the nuts to the rubber stand offs. I prefer to use Rivnuts (Goodyear) but I was out of #10s. This is a very nice mounting point right next to the power source it needs. An extension cable for the trigger lead long enough to reach the 3 terminal distributor connection on the left fender well is included. I simply lifted the leads that go to the original ignition and replace them with the MSD leads. I had to extend the coil leads a bit to reach the ignition coil. The coil used is an Accel SuperCoil (highly recommended). I simply lifted the existing wires from the coil and connected the new ones. This way, I could activate the old system by reconnecting 4 wires.

 

I fired the engine off and the first thing I noticed was that the timing was advanced >10 degrees over what it was with the old system. A scope showed that the MSD contains a true zero-crossing detector that gives rock stable triggering. Apparently the old system triggers on the trailing slope of the reluctor output. The jitters I've always seen with a timing light and always attributed to slop in the distributor is completely gone. The timing marks are absolutely stable.

 

The second thing I noticed is that the timing setting has a relatively small effect on idle speed or smoothness. Apparently the extended spark duration covers up minor timing errors.

 

After a brief test run, I removed the spark plugs and set the gap to about 0.080" - about as wide as I dared. This made a remarkable difference. I then did my usual timing tuning of setting the timing to the most static advance that was tolerated without pinging at WOT.

 

With the combination of the MSD ignition and the wide plug gaps, the car has a whole new personality. IT starts instantly even after hot soaking. The slight flat spot off idle is gone. There is perceptibly more power throughout the power range but especially down low.

 

I followed this work up with my standard distributor modification as follows. The early Zs are limited by the quality of fuel as to the amount of static advance tolerated. And it will tolerate proportionally less centrifugal advance at WOT. Therefore the need is to increase the degree of vacuum advance and decrease the span of centrifugal advance.

 

The centrifugal advance is easy to handle - simply get a California model advance mechanism from the D6F4-03 distributor. This advance unit is limited to 8.3 deg advance vs. the 10 deg. of the 48 states version.

 

The vacuum advance requires a bit more work. The advance mechanism is adjustable but the adjustment is sealed under epoxy on the vacuum diaphragm assembly. So the first step is to pick out all of this epoxy. I use a sharpened welding rod and some leather gloves. Underneath you will find 2 concentric screws. The inner screw is a travel limit and the outer one effects a minor adjustment on the spring preload.

 

Before you chip out the epoxy, you will probably want to measure the default setting. You will need some form of measured vacuum and a dial indicator to measure stroke. I set the diaphragm assembly up in a vice and applied a dial indicator to the shaft. A combination hand vacuum pump and gauge purchased at PEP Boys for the purpose supplied the vacuum. Here are typical default parameters.

 

Start of motion: 11" hg

 

End of motion: 17" hg

 

Total motion: 0.087"

 

This motion produces about 7.5 degrees of distributor (14 degrees crank) advance for a manual transmission. The automatic is calibrated slightly less. See page EE-29 in the 1975 service manual.

 

I've found that a typically near-stock engine will benefit from as much as twice the stock vacuum advance. Therefore, I adjust the travel stop (inner) screw to allow 0.150" of travel. So the modified specs are typically:

 

Start of motion: 10" hg

 

End of motion: 21" hg

 

Total motion: 0.150"

 

A holly carburettor will never make a full 21" of vacuum on the ported vacuum line so the full advance is never realised. Nonetheless, there is more than enough advance at light throttle settings where it is really needed. The results of all these modifications are as follows:

 

The subjective feel of the car is great. It now has an "eagerness" to rev which stems from a greatly enhanced part throttle torque characteristic. Its off-idle torque is extremely solid without any hint of flat spots. In-Traffic performance is vastly better (an absolute MUST here in Atlanta The car gained about 5" of manifold vacuum at cruise. It gained an immediate mileage increase of at least 5 mpg (measured over 2 tanks so far.) Carby retuning should improve that even more. The car willingly revs to the red line and makes useful power along the way.

 

I'd term the addition of the MSD system and the accompanying distributor work the second most profound thing I've done to the car behind replacing the trash SU carbs with the holly. I HIGHLY recommend this modification. The MSD ignition system can be had mail order for about $130.

 

* SWAPPING 240Z POINT-TYPE DISTRIBUTORS WITH 260/280Z ELECTRONIC TYPE DISTRIBUTORS:

 

Datsun used electronic distributors beginning with the '74 260Z. There is a star-like mechanism (variable reluctor) on the shaft and a pickup coil where the points used to be. When the points of the star align with the coil pole piece, the reluctance of the magnetic path is radically changed and that induces a pulse in the coil. The later model distributors are slightly larger than the points ones, a desirable property. They are cheap from salvage yards so that is the recommended course of action rather than trying to back fit a pickup to a points distributor.

 

The cheapest system is to get a 75 or later electronic distributor from the junkyard and use a chrysler ignition module and an Accel super coil. The diagram at the end of this article illustrates how to go about hooking it up.

 

* USING CRANK-TRIGGER/DIGITAL/DIRECT FIRE IGNITIONS:

 

For the high-RPM (>7000) or high compression racing engine these alternatives make sense. They do not make sense for any realistically streetable engine. Crank trigger uses a trigger mechanism mounted directly off the crankshaft for ignition timing. Some feel that the stock distributor, while "crank driven", can induce some sloppiness at 7000+ RPM due to the distributor shaft/gear setup used to drive the distributor from the crank. Crank trigger systems are available (I believe) from Nissan Motorsports and Electromotive.

 

For high compression engine builds (11:1 or better), it makes sense to use either a digital knock retard or a direct fire digital ignition. A high compression engine with tuned intake and exhaust needs less advance at high RPM and throttle where the resonances are working than it does below. A crude effort to address this are the boxes like MSD's timing computer and various mechanical high speed retard schemes.

 

There are a couple of good digital ignitions on the market including

 

Electromotive and the MOTES from Australia. The MOTES and one model of the Electromotive are actually engine management systems that also control injection but the digital ignition functionality is very good. Both use look up tables that are vectored into by engine speed and load. Both will accept knock sensor input.

 

Another alternative is the direct fire digital ignition construction series by Tim Drury. His system is based on a 68hc11, can trigger from a crank trigger or shaft encoder, is distributorless and uses the Motorola MC3334 intelligent coil management chip for the actual ignition trigging.

 

-------------------------------------------

 

Q:What are some common problems areas with Z car ignitions.

 

A: The stock Z car ignition system does not have any particular weaknesses that cause high failure rates or problems. The 240Z point ignition is prone to peculiarities resulting from the use of point technology, but these would be similar to other point-style systems. The Z car distributor cap is small, which makes it more prone to spark jumping if you are not careful about how much voltage is being sent to the cap (too high voltage resulting from non-resistive wires with non-stock coil, etc.).

 

Because the distributor (and hence most of the ignition circuitry) is forward mounted, it is easy to get wet, causing poor performance until it dries out. Couple that with a cracked cap, or poor sealing wires, and the problem compounds. Also, as the cars age, any and all electrical connections can be suspect, which will cause any number of ignition intermittents from partial to complete ignition loss. These problems can be especially difficult to diagnose as they may be heat, RPM, or time-intermittent, or any combination thereof.

 

Edited by Salman SHAMI

 

 

On Thu, 24 Nov 1994, wrote:

 

> Why is it that the vacuum _advance_ would retard the ignition? Is this

> because when you set up the curve, you have to take into account vacuum

> and then when you go WOT, you lose the advance you had taken into account

> at other throttle positions? Couldn't you setup the curve that you lised,

> and then add vacuum advance for better part-throttle running? If this

> leads to pinging, you could always reduce the amount of vacuum by

> bleeding it off or modifying the vacuum advance unit itself.

 

Depending on the type of vac adv you either have no vac adv at idle and

then full vac adv at part throttle (the vac port is just above the

throttle plate at idle and any opening of the throttle plate exposes the

port to vac), and then decreasing vac as the throttle is opened further;

or you have full vac adv at idle (the vac port is in the manifold) and

decreasing vac as the throttle is opened. Either way, at part throttle

(just off idle), light load cruise you have max vac adv and less than that

if you open the throttle further. With the vac hooked up you would open

the throttle to get a little more power and loose some advance (and

therefore some power) untill the engine speed increased and the mechanical

advance bumped the adv up. This slight delay in adv does cause a slight

hesitation. If the curve is set right without vac, any added adv from vac

is going to lead to pinging problems, so you would have to "detune" the

advance so that timing is right for light throttle, full load conditions

with the vac adv. It would then be too retarded at full throttle (and most

other operating conditions).

 

What I've just outlined is not exactly acurate, but it is close enough

for this disscusion. My point is this; a mechanical advance is a speed

(engine) sensitive regulator, a vac adv is a throttle position/load

sensitive device. They tried to use the two to run the ignition right up

to the edge of detonation. Problem is it won't work for that. There are

other factors that will bring the vac adv into play that do not relate to

the engine's proximity to detonation. To me the way to go is to run the

optimum mechanical adv (optimum for acceleration) and run either A) gas

with high enough octane, or water injection to control detonation (it

has both speed (engine) and load (manifold vac) sensors so that it will

function the same as the vac adv, but it does not have as detrimental an

effect on performance), or C) an electronic anti-knock device (a piezeo

sensor hears the knock and retards the timing, thereby relating timing

directly to what you are trying to control, namely engine knock). These

choices are in (my) oreder of preference by the way. The higher octane

gas will let you extract max power and so is my first choice. The water

injection does have the advantage of helping to keep the combustion

chamber clean, and provides nearly the performance of the high octane

gas. The anti-knock will prevent knocking (mostly) but engine power is

limited to the knock point of the fuel used. Its one advantage is it

would let you use varying octane fuels without having to adjust the

timing, provided the advance was set up for the highest octane fuel, and

the lower octanes did not cuase knocking at a point beyond the ability of

the anti-knock to compensate for. I don't know what the effects would be

from having the anti-knock functioning (retarding the timing for

lower octane gas) most of the time.

 

I suggested in a news group once that a piezeo sensor hooked up to a

water injection system (and maybe to the reatrded point set if a dual

point dist is being used) might be a good way to control knock. There are

also cockpit adjustable timing devices that let you quickly and easily

reset timing for varying conditions (temp, octane, etc.). This would also

be good for a car that is driven daily on regular pump gas and then raced

on higher octane gas on the weekend. I just don't see why anyone would

trouble with a vac adv when it won't do what is required of it and other

things will.

 

Marc Sayer

Performance Engineering

 

On Fri, 23 Dec 1994, Andrew Leonard Levy wrote:

 

> Here is tip about the later electronic dist. vac. adv. units, they are

> fully adjustable by removing the epoxy putty from the end. Inside there

> are two srews, the center one is the travel limiter, this will limit the

> amount of advance. The outer srew adjusts the spring seat pressure. If

> you have a timing light and mighty vac pump you can tailor the vac adv.

> to work well with most setups i.e mikunis and weber dcoe.

>

 

Kelvin Dietz and I had talked about his once, but I have never played

with it because I was under the impression that only the spring preload

was adjsutable. If you can really adjust not only at what man pressure

the thing starts to work (spring preload), but also how much total adv it

can add, then it would resolve one of my major bitches re: vac adv. Just

slapping a stock vac adv on your dist and expecting it to br correct for

your application is as silly as just slapping some lashpads in and

expecting them to work with your cam etc. Most stock vac adv's add way

too much adv for a Weber/Mikuni set up, and this forces you to retard the

static timing so that on those light load accelerations you don't get

knocking. This causes the power output to drop on full acceleration, blah

blah blah, yada yada yada. With this full adjustability you could make a

vac adv work much better, in fact you could almost make it work right. A

temp sensor in the system would still help but at least with this you can

make the vac adv work with the mechanical adv, and engine requirements.

Thanks for the info.

 

Oh by the way, you do get ported advance with an SU, it just behaves a

little different that it would with an accelerator pump type carb. In

esscence the only difference between ported and manifold vac is that

there is no vac at idle with a ported system and there is with a manifold

system. I forget who it was who said they had never heard of or seen a

manifold vac advance, look at any MGB from about 1972-1976. The key is if

the tune up instructions tell you you must disconnect the vac adv when

you set the ignition timining then it may well be a manifold vac source

they are using. This is because there is no vac adv at idle with a ported

vac adv (if you have your throttle plates positioned correctly, ie you

don't have the idle speed set so high that the ports are exposed at

idle), whereas there is full vac adv at idle with a manifold vac adv. The

resason they went to port vac (as far as I know) is for emmissions

purposes, the high adv at idle created higher emmisions of some gases

(don't know or care which ones) and on decceleration vac adv was also too

high. Then when they added pop off valves in the throttle plates (or the

BCDD crap on the Datsuns) this started screwing with the manifold vac adv

and they were having all sorts of problems.

 

My other bitch about stock vac adv is that with a really radical cam the

off idle vac signal is nothing like it was stock and the stock pressure

settings are of no value. This is especially bad if you have a manifold

vac source, because the vac readings at idle fluctuate so much with a

radical cam that your vac adv will be jumping all over the place. This

makes for a lousy idle, and off idle behavior will be weird too. This is

why even with an adjsutable vac adv I still would not use vac adv if the

vehicle had to have manifold vac as its vac source.

 

The other thing I would like to see with a vac adv is that the vac adv be

locked out above a certain speed. Otherwise your total adv will be too

high, or your static will be too low.

 

ie; static setting 20 degrees, mechanical adv 16 degrees, vac adv 10

degrees. At 4000 RPM (full mechanical adv)

 

20 + 16 = 36 -- no problem here, full throttle full load works fine

20 + 16 + 10 = 46 -- way too much total adv at high speeds and low loads

 

now take 10 degrees static (to allow for the correct total adv figure)

 

10 + 16 = 26 -- need the vac adv in order to have enough total adv, so at

full throttle full load we don't have enough total adv

10 + 16 + 10 = 36 -- no problem at full throttle light load

 

If the vac adv was locked out at the same speed as full mechanical adv

was acheived, this would not be a problem. But it also might not solve the

knock question at all speeds/loads/temps.

 

Oh God I've started it up again, no no shoot me please.

 

Marc Sayer

Performance Engineering

 

________________________________________________

||||||||||||||| ANDREW ||||||||||||||||

------------------------------------------------

 

S.U. carbs have a vac. port in the correct location to be a ported

vac. source, the problem is that they are a constant velocity carburator

which means that the air speed is constant inside the venturi. the

effect is that the vac. signal between the venturi and the throttle plate

will not be affected by the load in the correct manner. What makes vac.

adv. even less compatiable S.U. carbs is the dampening of the slide.

One thing to remember is that vacuum advance is as american as

apple pie. Because of this it was designed for fixed venturi carbs

that came on cars from Detroit. So for this reason lets look at how

a arbitrary american dist (mid 70s vintage) operates. Here are some advance

specs. 6 intial, 24 mech. 8 vac degrees, there is a difference between

total adv. and max adv. At max rpm this eng. would see 30 degrees of

ignition advance but under moderate load like when accelerating when

combustion is slow the ignition timing could be as high as 38 degrees.

Now under heavy loads the engine may not make enough ported vac. to

activate all of the vac. adv. therefore the igntion timing will be less

then 38. At cruise the vac. adv. should not function so the igntion timing

should be 30 or less depending on the rpm when the mech adv. is all in and

the engine rpm. Here is a little proof of why less ign. timing is better at

cruise. I'm sure that you have experienced an engine that would not start

because it was to far advanced, the starter motor could not turn the engine

over. The same thing happens at cruise if you generate to much cylinder

preasure before T.D.C. ( negative work ). In order to net positive work,

the amount of pressure needed after T.D.C. will be what ever pressure is

generated before T.D.C. plus what is needed to drive the vehicle. So the

goal is to make as little power as possiable. Since the power you

need to drive a car is a constant the only thing that can be changed is

how much negative work is being produced. so the less the better.

The reason that emission regulated cars do not have alot of

intial timing is to reduce the amout of carbonmonoxide that is produced at

idle..

One last bit, It is difficult to remove the putty from the vac. adv.

units, here are some tips that might help. Its better to remove the unit from

the dist. I usally start with a wire brush on a drill or a bench grinder

this will take it down so it flush with the unit. At this time I use a

little knife or screw driver to wittle the putty out. You have to get all

the threads and slots perfectly clean before either of the screws will move

be careful not damage the threads or you will end up with a vacuum leak.

Make sure you use the correct srew driver blade width and one with low side

taper, this is critical, 10mm, 7mm. after they are removed you should

chase the large thread with a 12mm, 150 pitch tap. when assembling the unit

use teflon tape, telflon sealer or what ever else will seal the threads.

 

 

**********

 

On Sat, 24 Dec 1994, Andrew Leonard Levy wrote:

 

>

>

> S.U. carbs have a vac. port in the correct location to be a ported

> vac. source, the problem is that they are a constant velocity carburator

> which means that the air speed is constant inside the venturi.

 

No the air speed at the jet bridge is constant, not at the throttle plates

or port location. Many British SU set ups do use ported vac adv.

 

> the

> effect is that the vac. signal between the venturi and the throttle plate

> will not be affected by the load in the correct manner. What makes vac.

> adv. even less compatiable S.U. carbs is the dampening of the slide.

 

This does alter the drop rate of the vac adv some and is why you can not

mix and match manifold & port vac cannisters. But it does not preclude

the use of ported vac adv w/SU's

 

> One thing to remember is that vacuum advance is as american as

> apple pie. Because of this it was designed for fixed venturi carbs

> that came on cars from Detroit.

 

I don't know that I agree with this at all. Vac adv is used by all sorts

of car makers, including foreign. As I have said many times here, British

cars have been using vac adv and CV carbs for ages.

 

So for this reason lets look at how

> a arbitrary american dist (mid 70s vintage) operates. Here are some advance

> specs. 6 intial, 24 mech. 8 vac degrees, there is a difference between

> total adv. and max adv. At max rpm this eng. would see 30 degrees of

> ignition advance

 

No max adv will also depend on load/throttle position and could be as

high as 38, but you say this very thing in the next sentence which seems

to be contradictory.

 

but under moderate load like when accelerating when

> combustion is slow the ignition timing could be as high as 38 degrees.

> Now under heavy loads the engine may not make enough ported vac. to

> activate all of the vac. adv. therefore the igntion timing will be less

> then 38. At cruise the vac. adv. should not function

 

Oh yes it will, and it will be functioning whether it is a port source or

a manifold source, the only difference will be the exact ammount of vac

signal applied to the canister.

 

so the igntion timing

> should be 30 or less depending on the rpm when the mech adv. is all in and

> the engine rpm. Here is a little proof of why less ign. timing is better at

> cruise.

 

Do some studying, light throttle cruise is eaxctly when you do want the

vac adv to advance the timing. It is when the engine is heavily loaded

(full throttle accel or other high load conditions) that less advance is

called for. You use starting as an example but the starting process is

completly unrelated to the running process. And in fact durring the start

process, you have less adv than at any other time because the vac adv is

either not operating (ported vac) at all or has so little signal applied

to it due to slow engine speed (manifold vac) that it adds little or no

adv. Additionally, due also to the slow engine speed, there is very

little mechanical adv. The problem you are describing is one in which the

static adv is so high that the piston is still coming up when ignition

takes place. This is due to the slow piston speed involved at cranking

RPM's and is why a hard start engine (due to too much static adv) will

still run and idle well once started. But your basic premiss that too much

adv will hurt engine output is true, its just true for all states and

doesn't explain why you think the engine needs less adv at light throttle

cruise. This is a major area we are getting into now and I am not willing

to spend the time on it. Read up and you will see that more adv is needed

at light throttle cruise than when the engine is loaded. If anyone else

wants to talk more on this please do.

 

I'm sure that you have experienced an engine that would not start

> because it was to far advanced, the starter motor could not turn the engine

> over. The same thing happens at cruise if you generate to much cylinder

> preasure before T.D.C. ( negative work ). In order to net positive work,

> the amount of pressure needed after T.D.C. will be what ever pressure is

> generated before T.D.C. plus what is needed to drive the vehicle. So the

> goal is to make as little power as possiable. Since the power you

> need to drive a car is a constant the only thing that can be changed is

> how much negative work is being produced. so the less the better.

> The reason that emission regulated cars do not have alot of

> intial timing is to reduce the amout of carbonmonoxide that is produced at

> idle..

> One last bit, It is difficult to remove the putty from the vac. adv.

> units, here are some tips that might help. Its better to remove the unit from

> the dist. I usally start with a wire brush on a drill or a bench grinder

> this will take it down so it flush with the unit. At this time I use a

> little knife or screw driver to wittle the putty out. You have to get all

> the threads and slots perfectly clean before either of the screws will move

> be careful not damage the threads or you will end up with a vacuum leak.

> Make sure you use the correct srew driver blade width and one with low side

> taper, this is critical, 10mm, 7mm. after they are removed you should

> chase the large thread with a 12mm, 150 pitch tap. when assembling the unit

> use teflon tape, telflon sealer or what ever else will seal the threads.

>

> Andy Levy: Merry Christmas, Happy Holidays, Happy New Year

 

For the very useful info on the vac adv adjsutment I do thank you Andy,

and I hope that you don't take offense at my not wanting to spend any

more time on the question of when the engine needs more adv. Its just

that this has been beaten to death once here on the Z car list and

several times on other lists I subscribe to, and on the rec.autos.tech

news group. I have to limit the time I spend at the computer and so I

must be selective. I hope that some others in the group will pick up on

this thread with you. I want to wish you and all the good people I have

met on the net these last few months a very sincere Happy Holidays.

 

Marc Sayer

Performance Engineering

 

 

On Sun, 25 Dec 1994, wrote:

 

> On Sat, 24 Dec 1994, wrote:

>

> > S.U. carbs have a vac. port in the correct location to be a ported

> > vac. source, the problem is that they are a constant velocity carburator

> > which means that the air speed is constant inside the venturi.

>

> No the air speed at the jet bridge is constant, not at the throttle plates

> or port location. Many British SU set ups do use ported vac adv.

 

I did not say throttle plate. I said venturi which is the space between

the bottom of the slide and the carb floor, this is where the needle jet

is located. This is the area that can vary in size. This is why S.U.s are

a variable venturi carburator. This why it does not have true ported

vacuum source..

 

 

> > the

> > effect is that the vac. signal between the venturi and the throttle plate

> > will not be affected by the load in the correct manner. What makes vac.

> > adv. even less compatiable with S.U. carbs is the dampening of the slide.

>

> This does alter the drop rate of the vac adv some and is why you can not

> mix and match manifold & port vac cannisters. But it does not preclude

> the use of ported vac adv w/SU's

 

You lost me on this one.

 

>

> > One thing to remember is that vacuum advance is as american as

> > apple pie. Because of this it was designed for fixed venturi carbs

> > that came on cars from Detroit.

>

> I don't know that I agree with this at all. Vac adv is used by all sorts

> of car makers, including foreign. As I have said many times here, British

> cars have been using vac adv and CV carbs for ages.

>

Well you dont have to agree, but the fact is that vacuum advance was design

by one of the major car man. in Detroit ( I think Crysler corp. ) in the 50s.

It was adopted and adapted by foreign auto man.

 

> > So for this reason lets look at how

> > a arbitrary american dist (mid 70s vintage) operates. Here are some advance

> > specs. 6 intial, 24 mech. 8 vac degrees, there is a difference between

> > total adv. and max adv. At max rpm this eng. would see 30 degrees of

> > ignition advance

>

> No max adv will also depend on load/throttle position and could be as

> high as 38, but you say this very thing in the next sentence which seems

> to be contradictory.

 

What I said is correct, I left out some small details. At some point in

time the ported vacuum will equalize with the manifold vacuum. Of

course when an engine is operating at full thottle and accelerating

the manifold vacuum will approach a very low amount of vacuum. In some cases

the manifold vac. will go to 0 in.HG of vac. But ussally it will be a couple

in.HG of vac. that is why it ussally requires 5-10 in. HG of vac. to

intiate any movement from a vacuum advance unit.

 

> >but under moderate load like when accelerating when

> > combustion is slow the ignition timing could be as high as 38 degrees.

> > Now under heavy loads the engine may not make enough ported vac. to

> > activate all of the vac. adv. therefore the igntion timing will be less

> > then 38. At cruise the vac. adv. should not function

>

> Oh yes it will, and it will be functioning whether it is a port source or

> a manifold source, the only difference will be the exact ammount of vac

> signal applied to the canister.

 

The vac. advance will function. It should not be functioning at its maxium .

That is why I said less than 38 degrees.

This is the area that has given vacuum advance a bad rep. The main reason

that engineers did not, or did not want to, take into account the many

different climates, air desities and fuels. The reason I believe that

these systems are designed on the ragged edge of reality is because

of the C.A.F.E. requirements. The engineers are supposed to make a control

system that will yield the highest mpg. whats wrong is that they only care

about the optimum situation. Not the average.

 

 

> so the igntion timing

> > should be 30 or less depending on the rpm when the mech adv. is all in and

> > the engine rpm. Here is a little proof of why less ign. timing is better at

> > cruise.

>

> Do some studying, light throttle cruise is eaxctly when you do want the

> vac adv to advance the timing. It is when the engine is heavily loaded

> (full throttle accel or other high load conditions) that less advance is

> called for. You use starting as an example but the starting process is

> completly unrelated to the running process. And in fact durring the start

> process, you have less adv than at any other time because the vac adv is

> either not operating (ported vac) at all or has so little signal applied

> to it due to slow engine speed (manifold vac) that it adds little or no

> adv. Additionally, due also to the slow engine speed, there is very

> little mechanical adv. The problem you are describing is one in which the

> static adv is so high that the piston is still coming up when ignition

> takes place. This is due to the slow piston speed involved at cranking

 

Ignition allways starts before TDC now however combustion and max

cylinder presure should be after TDC if it was not the engine would turn

backwards even with starter trying turn over the motor. The important

part is how to net positive amount of power efficiently at cruise.

 

Andy:

---------------------

 

Everyone follow closely here cause we are now three steps deep in "I said

- you said"

 

> On Mon, 26 Dec 1994, wrote:

>

>

>

> >On Sun, 25 Dec 1994, wrote:

>

> > > On Sat, 24 Dec 1994, wrote:

> >

> > > S.U. carbs have a vac. port in the correct location to be a ported

> > > vac. source, the problem is that they are a constant velocity carburator

> > > which means that the air speed is constant inside the venturi.

> >

> > No the air speed at the jet bridge is constant, not at the throttle plates

> > or port location. Many British SU set ups do use ported vac adv.

>

> I did not say throttle plate. I said venturi which is the space between

> the bottom of the slide and the carb floor, this is where the needle jet

> is located. This is the area that can vary in size. This is why S.U.s are

> a variable venturi carburator. This why it does not have true ported

> vacuum source..

 

Andy, ported vacum has nothing to do with the vac signal at the venturi.

It is a small port just upstream of the throttle plate's postition at

idle. It will have no (or almost no) vac signal at idle because the

throttle plate is between it and the vac source. As soon as the throttle

is opened (even slightly) the vac port is exposed to manifold vac, and

as long as the throttle plate is open the port vac signal will match the

manifold vac signal. Just like the progression ports in a carb (other

than CV carbs which don't use progression ports), the vac signal at the

port has nothing to do with the vac signal at the venturi.

 

>

>

> > > the

> > > effect is that the vac. signal between the venturi and the throttle plate

> > > will not be affected by the load in the correct manner. What makes vac.

> > > adv. even less compatiable with S.U. carbs is the dampening of the slide.

> >

> > This does alter the drop rate of the vac adv some and is why you can not

> > mix and match manifold & port vac cannisters. But it does not preclude

> > the use of ported vac adv w/SU's

>

> You lost me on this one.

 

The drop rate is the rate at which the vac signal will drop when the

throttles are opened. And this will control how much and how quickly the

ignition will be retarded. With an accelerator type carb (other than a

carb with vac operated secondary(s)), the vac signal will drop off very

rapidly. With an SU the drop off is slower. Carbs with vac operated

secondary(s) will drop off differenrtly from either mechanical linkage

accelerator pump carbs or CV type carbs. This is one reason why a vac

canister from a progressive 2 barrel carb with a vac actuated secondary

(such as the stock 510 carb) will often not work well with a mecanically

linked 2 barrel such as the Mikuni. Another problem is encountered when

going from a single carb application to a multi carb application. The vac

signal in a single carb manifold (at least one like the 510 where a large

plenum is used) is smoothed out by having all 4 cylinders feeding into the

plenum. On a multi carb set up such as a dual Mikuni, the ported vac is

fed by only one cylinder and so the vac signal is uneven and pulses quite

a bit. This is one reason why a balance tube should be installed. But the

balance tube will not completely smooth out the vac signal and so the

stock vac canister will not work as well as it would on the single carb

set up. This also applies to dual SU's to a lesser extent (the volume of

the balance tube in a dual Su manifold is much larger (proportionally at

least) than those used in the dual Mikuni/Weber manifolds and so the

effect is lessened.

 

> > > lets look at how

> > > a arbitrary american dist (mid 70s vintage) operates. Here are some advance

> > > specs. 6 intial, 24 mech. 8 vac degrees, there is a difference between

> > > total adv. and max adv. At max rpm this eng. would see 30 degrees of

> > > ignition advance

> >

> > No max adv will also depend on load/throttle position and could be as

> > high as 38, but you say this very thing in the next sentence which seems

> > to be contradictory.

>

> What I said is correct, I left out some small details. At some point in

> time the ported vacuum will equalize with the manifold vacuum. Of

> course when an engine is operating at full thottle and accelerating

> the manifold vacuum will approach a very low amount of vacuum. In some cases

> the manifold vac. will go to 0 in.HG of vac. But ussally it will be a couple

> in.HG of vac. that is why it ussally requires 5-10 in. HG of vac. to

> intiate any movement from a vacuum advance unit.

>

> > >but under moderate load like when accelerating when

> > > combustion is slow the ignition timing could be as high as 38 degrees.

> > > Now under heavy loads the engine may not make enough ported vac. to

> > > activate all of the vac. adv. therefore the igntion timing will be less

> > > then 38.

> > > *****At cruise the vac. adv. should not function*****

> >

> > Oh yes it will, and it will be functioning whether it is a port source or

> > a manifold source, the only difference will be the exact ammount of vac

> > signal applied to the canister.

>

> The vac. advance will function. It should not be functioning at its maxium .

> That is why I said less than 38 degrees.

 

Now I'm confused, you originally said that at cruise the vac adv should

not function (I moved and starred this quote above for clarity), and I

replied that it would be functioning at cruise. Now you seem to be

saying I was right and it will. Fact is that is the only time you will

ever get full vac adv in a ported system.

 

>

>

> > so the igntion timing

> > > should be 30 or less depending on the rpm when the mech adv. is all in and

> > > the engine rpm. Here is a little proof of why less ign. timing is better at

> > > cruise.

> >

> > Do some studying, light throttle cruise is eaxctly when you do want the

> > vac adv to advance the timing. It is when the engine is heavily loaded

> > (full throttle accel or other high load conditions) that less advance is

> > called for. You use starting as an example but the starting process is

> > completly unrelated to the running process. And in fact durring the start

> > process, you have less adv than at any other time because the vac adv is

> > either not operating (ported vac) at all or has so little signal applied

> > to it due to slow engine speed (manifold vac) that it adds little or no

> > adv. Additionally, due also to the slow engine speed, there is very

> > little mechanical adv. The problem you are describing is one in which the

> > static adv is so high that the piston is still coming up when ignition

> > takes place. This is due to the slow piston speed involved at cranking

>

> Ignition allways starts before TDC now however combustion and max

> cylinder presure should be after TDC if it was not the engine would turn

> backwards even with starter trying turn over the motor. The important

> part is how to net positive amount of power efficiently at cruise.

>

> Andy:

 

I should have said "when combustion takes place" to keep this clearer for

you. The point I was making is that the piston is moving so slowly that

the entire ingnition/combustion process will happen before the piston

reaches TDC. I thnik we are both in agreement here. Where we dissagree is

whether this has anything to do with a running condition. You claim it

does and use it to explain why you think the timing should be retarded

(this is a statement of relative change not absolute condition, if the

timing is 20 degrees BTDC and I change it to 10 degrees BTDC the timing

has been retarded) at cruise. I say that it has nothing to do with

operating (running) conditions, and so does not support your contention.

Again I suggest that you do some reading, the very point of vac adv is to

adv the timing at cruise and retard the tinming when under heavier load.

At idle the timing is retarded (relative not absolute) in a ported system

but not in a manifold system. But at light throttle cruise both systems

add full vac advance.

 

I swear this is the last time I will post on this subject, please someone

else help Andy out here and set him straight on vac adv. I just don't

seem able to explain myself to him. I am sure he will understand it once

it is made clear to him, heck he may understand it now and it may all be

a problem of semantics. Whatever the case I have to pull out of the

thread, so someone else please see if you can get it cleared up.

 

Andy, don't take offense, cause none is intended. I am just swamped with

"net" work. I am not trying to insult your intelligence here either,

quite the opposite, you seem to be a very knowledgeable guy and the info

re: the vac can adjustments was greatly appreciated. I just think you are

either confused about how vac adv works in these cars or I am not

understanding you. Either way, I want to make clear that I am not putting

you down at all. Its been fun talking with you and I hope you will

continue to keep me on my toes.

 

Marc Sayer

Performance Engineering

 

 

 

On Thu, 22 Dec 1994, wrote:

 

> Vacuum Advance Purpose:

> Also remember that the vacuum

> is a 'ported' source, not a manifold source. I spotted on 'Hot Car Rag'

> magazine that explained why NOT to use vacuum advance, and proceeded to

> explain MANIFOLD vacuum. Arrg, hard to get decent technical information.

 

On Datsuns this may be true but on many other cars manifold vac was used.

The main difference is whether there is any vac adv applied at idle. Once

off idle it behaves very similarly to ported vac.

 

>

> Leo - sounds like your Chevy really should be recurved, or retard the

> timing a little during hot weather. I run my 510 right up to the edge

> on the advance... great on cool days... but I get a little pinging on

> those hot afternoons.

 

This is one reason why I don't care for vac adv. A smart vac adv tied to

other sensors such as ambient temp, would offer the sort of maxed control

that everyone seems to expect from a vac adv. On occassion I have said I

didn't care for vac adv, and that I felt there were other ways to keep the

ignition "up against the knock limit". What I should have said was dumb

vac adv systems such as used by the manufacturers of our cars. These sort

of fixed adv systems where neither the pressure settings nor the degrees

of adv are adjustable, and which are too dumb to know that the car needs a

different curve when its hot than it does when it cold out are the types

of vac adv I don't care for. On most Weber sidedrafts there is too much

adv added by the vac adv (or conversely too much retard, when the

throttles are opened). A vac adv system with a cylinder head temp sender

controling the "no vac" setting would be an advantageous addition, but

even a bi-metal spring doing the same thing would be a big help.

 

IMHO

 

Marc Sayer

Performance Engineering

 

[NewZed]

My butt says the engine runs out of poop around 2500 rpms.

 

WOT optimally in my opinion should be close to 12.5:1 afr NOT 16.8:1 with idle sitting at 10:1 afr.

 

I'm just a rookie myself, and don't even have an AFR gauge. But 16.8:1 AFR looks like you're running out of fuel, in addition to timing issues, if that AFR is what you are seeing when you open the throttle.

 

Edit - I don't have much experience with carbs either so can't offer any solutions, just an observation.

Edited December 3, 2010 by NewZed

[rayaapp2]

I'm just a rookie myself, and don't even have an AFR gauge. But 16.8:1 AFR looks like you're running out of fuel, in addition to timing issues, if that AFR is what you are seeing when you open the throttle.

 

Edit - I don't have much experience with carbs either so can't offer any solutions, just an observation.

 

 

Thats basically the limit of the needle and main jet as that is what limits AFR at WOT. My guess is that the 240Z SU's were designed for a smaller engine and the AFR problems are why Nissan came out with the flat top carbs with an isolated idle circuit and a larger venturi in latter cars.

[rayaapp2]

Your problem is most likely ignition related. Here are a couple old posts from the Internet Z Car Club that I archived:

 

 

I suspect that something is up with the timing, but I have not been able to figure it out.

Is there a timing curve map for this engine anywhere? At least that would give me something to go from.

 

Thanks for all that info johnc!

 

I had a chance to read through most of it. I had to rush off to work and Ill get through the last quote in a little bit.

 

 

Im using a stock L24 distributor with a pertonix pointless ignition and a MSD blaster 2 coil on Accel 8mm wires, NGK split fire BPR6EY (now stock heat range) plugs @ .036". The Static Timing is set at 10° BTDC @ 750rpm(timed for "C" cam not stock "A" @ 17° @ 650rpm).

 

Specs for my L24 D606-52 distributor advance are

 

Mechanical starts 450rpms ends 1000 rpms with a total of 6°

Vacuum starts 100mm Hg ends 245mm Hg with a total of 5.5°

 

Degrees read off Crank

Here is what Im seeing with NO LOAD:

Mechanic

Idle @ 750rpm 10°

1350 still 10°

1500 15°

1700 20°

2000 25°

2300 30°

2600 35°

above that it stays around 35° but gets occasional flux above

 

with Vac adv on

Idle 10°

1400 15°

1700 20°

2000 25°

2300 30°

2500 35°

 

Vacuum ONLY at idle

250mm Hg add 5°

400mm Hg add another 5°

 

 

This is AFTER I flipped the rotor shaft! This is not what I was seeing before. Im getting more advance and higher up in the RPM range.

Something else I forgot to mention. The timing chain is on its last leg. The cam gear is on notch #3, but is timed correctly there. If only I had a degree wheel(I have a dial gauge) and a cam card I could set that info in stone. Degree wheel is on my wish list for christmas! I mean how else am I going to setup a custom ground cam right?

 

 

I have a MSD 6A laying around that I may try eventually, but Im not trying to compound anything just yet.

I believe I connect the Pertonix unit up just like points no like electronic pickup style to the MSD unit.

I should be able to open the gap up on the plugs after installing the MSD.

Edited December 4, 2010 by rayaapp2

[ozconnection]

I suspect that something is up with the timing, but I have not been able to figure it out.

Is there a timing curve map for this engine anywhere? At least that would give me something to go from.

 

Thanks for all that info johnc!

 

I had a chance to read through most of it. I had to rush off to work and Ill get through the last quote in a little bit.

 

 

Im using a stock L24 distributor with a pertonix pointless ignition and a MSD blaster 2 coil on Accel 8mm wires, NGK split fire BPR6EY (now stock heat range) plugs @ .036". The Static Timing is set at 10° BTDC @ 750rpm(timed for "C" cam not stock "A" @ 17° @ 650rpm).

 

Specs for my L24 D606-52 distributor advance are

 

Mechanical starts 450rpms ends 1000 rpms with a total of 6°

Vacuum starts 100mm Hg ends 245mm Hg with a total of 5.5°

 

Degrees read off Crank

Here is what Im seeing with NO LOAD:

Mechanic

Idle @ 750rpm 10°

1350 still 10°

1500 15°

1700 20°

2000 25°

2300 30°

2600 35°

above that it stays around 35° but gets occasional flux above

 

with Vac adv on

Idle 10°

1400 15°

1700 20°

2000 25°

2300 30°

2500 35°

 

Vacuum ONLY at idle

250mm Hg add 5°

400mm Hg add another 5°

 

 

This is AFTER I flipped the rotor shaft! This is not what I was seeing before. Im getting more advance and higher up in the RPM range.

Something else I forgot to mention. The timing chain is on its last leg. The cam gear is on notch #3, but is timed correctly there. If only I had a degree wheel(I have a dial gauge) and a cam card I could set that info in stone. Degree wheel is on my wish list for christmas! I mean how else am I going to setup a custom ground cam right?

 

I run a 280zx distributor in my car. I have a few of these and they all seem to have slightly different advance curves. The one I like the best is the one that has only 12 degrees mechanical advance.

 

I set this on up with 22 degrees static timing at idle and get 34 degrees total advance at 2600 rpm.

 

I don't use any vacuum advance when timed this way.

 

Throttle response (torque) is excellent at lower to mid rpms. Fuel economy is very good with a well set up induction. Sort out your fuel delivery and get good mixtures all round. I see 13 AFR at idle at 800 rpm's, 15AFR's at light cruise and around 12.8 to 13.0 at wot.

 

I use Msd 6 and a Holley 465 cfm 4 barrel and a stock head and cam. This is a street engine and it runs very well.

 

A little cam advance is also good for low to mid range response. Replace the chain when you can.

 

Good luck with it.

[NewZed]

Ignition timing is one of those hard to understand areas that is made more difficult by the way the distributor data is reported.

 

As I understand things, the distributor turns at half crankshaft speed because the spark is only needed on every other up stroke. But the distributor data is reported in distributor shaft revolutions, so must be adjusted to tell you what is happening relative to the crankshaft. Therefore, the rpm reported should be doubled, because the cranksaft is going twice as fast as the distributor. And the degrees reported must be doubled, because the crankshaft travels 2 degrees for every one that the distributor does. The vacuum level is the same.

 

So your L24 D606-52 specs would be:

 

Mechanical starts 900 rpms ends 2000 rpms with a total of 12°

Vacuum starts 100mm Hg ends 245mm Hg with a total of 11°

 

With static at 10, you should get 33 degrees advance above 2000 rpm with over 245mm Hg (high rpm cruising) and 22 total at WOT above 2000 rpm. Your data is close to that, with wear and gummed up weights as possibilities for the 2 extra degrees and the higher rpm. But it looks like you had vacuum activated for both data sets.

 

This is my current understanding and I welcome any comments about whether it is right or wrong.

 

 

It seems to work for me, I have a DCF5-02 in my car with 17 (8.5 reported at the dist.) mechanical at 2500 rpm and 18 (9 reported at dist.) vacuum at 11.61" (295 mm) Hg. I'm running 17 static, so I'm at 52 and 34 (Edit - SHOULD be at 52 and 34, I don't have the right timing light to confirm), cruise and WOT, above 2500 rpm. I've heard not a knock or ping with 89 octane, but it is kind of cold here. I worked my way up a few degrees at a time and the engine got more responsive every time. I have a stock 1976 with EFI, but using a 1978 distributor.

 

I'm just throwing all of this out there for conversation, and might be repeating something already well-known, or maybe even wrong. It took me a while to figure out what was up with the various distributors and how the specs. were reported.

Edited December 4, 2010 by NewZed

[rayaapp2]

Ignition timing is one of those hard to understand areas that is made more difficult by the way the distributor data is reported.

 

As I understand things, the distributor turns at half crankshaft speed because the spark is only needed on every other up stroke. But the distributor data is reported in distributor shaft revolutions, so must be adjusted to tell you what is happening relative to the crankshaft. Therefore, the rpm reported should be doubled, because the cranksaft is going twice as fast as the distributor. And the degrees reported must be doubled, because the crankshaft travels 2 degrees for every one that the distributor does. The vacuum level is the same.

 

So your L24 D606-52 specs would be:

 

Mechanical starts 900 rpms ends 2000 rpms with a total of 12°

Vacuum starts 100mm Hg ends 245mm Hg with a total of 11°

 

With static at 10, you should get 33 degrees advance above 2000 rpm with over 245mm Hg (high rpm cruising) and 22 total at WOT above 2000 rpm. Your data is close to that, with wear and gummed up weights as possibilities for the 2 extra degrees and the higher rpm. But it looks like you had vacuum activated for both data sets.

 

This is my current understanding and I welcome any comments about whether it is right or wrong.

 

 

It seems to work for me, I have a DCF5-02 in my car with 17 (8.5 reported at the dist.) mechanical at 2500 rpm and 18 (9 reported at dist.) vacuum at 11.61" (295 mm) Hg. I'm running 17 static, so I'm at 52 and 34 (Edit - SHOULD be at 52 and 34, I don't have the right timing light to confirm), cruise and WOT, above 2500 rpm. I've heard not a knock or ping with 89 octane, but it is kind of cold here. I worked my way up a few degrees at a time and the engine got more responsive every time. I have a stock 1976 with EFI, but using a 1978 distributor.

 

I'm just throwing all of this out there for conversation, and might be repeating something already well-known, or maybe even wrong. It took me a while to figure out what was up with the various distributors and how the specs. were reported.

 

 

I think you may be correct about where they are reading the angles from. The page I pulled the specs from does not state angle of crank or distributor rotation for reference. It does state dwell angle just below so it may be safe to assume its distributor angles in which case double the spec and its close to what I ended up with, and that just makes more sense.

 

As far as vacuum goes. It was definitely disconnected and connected when I reported the info. I used my hand vacuum pump with gauge to activate the vacuum advance for the last data. I suspect I have a weak ported vacuum signal. The port may be clogged with carbon or the vacuum signal at it is to weak. Look at the amount of vacuum I had to apply to get full movement out of the vacuum advance. I just cleaned the plate that the vacuum advances moves in the distributor, but I havent touched the diaphragm itself. It may be adjustable as described in johnc's quote. Im not sure whats going on there yet.

[Tony D]

Thats basically the limit of the needle and main jet as that is what limits AFR at WOT. My guess is that the 240Z SU's were designed for a smaller engine and the AFR problems are why Nissan came out with the flat top carbs with an isolated idle circuit and a larger venturi in latter cars.

 

This is not really true. The needle and jet size can limit the flow of the fuel ultimately, but a single SU with a 0.100" jet can support FAR more horsepower than you will ever see on your L24. The stock Datsun SU would support a Crown Turbo Kit to about 12psi. Using a Jaguar 2" having a 0.125" jet would support the kit to well over 20psi. Do the math on the horsepower.

 

The thing is the fuel pumps are weak, and when yo ustart sucking hard on CV carbs the float bowl level drops. Put the site gauge into the float bowl in the little hex plug provided and do a dyno run---watch what happens to your float level.

 

Realize that a high pressure pump (something that can push 20psi) and a backpressure style fuel system can really help with keeping your float bowl level proper under hard load and high rpms.

 

Nissan came out with the flat tops because the mandate for idle emissions. it separated the idle from the main system in order to run a proper power taper on the main system, and put a finely controlled metering block in for use at idle. The power valve was supposed to work for interim 'accelerator pump substitution' by richening the transition so you didn't have a flat spot off-idle and bog. If the power valve takes a dump, you go rich. Really you can retaper the needle at the transition point to go rich when coming off the idle circuit, and still have proper AFR up to the top of the RPM range if you run a flat top.

 

But I digress...

[Tony D]

Im using a stock L24 distributor with a pertonix pointless ignition and a MSD blaster 2 coil on Accel 8mm wires, NGK split fire BPR6EY (now stock heat range) plugs @ .036".

 

 

Ray, you are SO CLOSE with this statement! You have just misphrased it slightly.

 

You realize in your statement that you have a "Pertronix Pointless Ignition" Which really I take to mean "Pertronix Pointelss Coverted Distributor"...

 

Really anybody using a Converted Pointless Distributor is close to realizing a Distributor is Pointless.

 

 

They are not the same thing...

 

You have a Pointless Distributor, now realize a Distributor is Pointless.

 

COP my man...COP!

[rayaapp2]

This is not really true. The needle and jet size can limit the flow of the fuel ultimately, but a single SU with a 0.100" jet can support FAR more horsepower than you will ever see on your L24. The stock Datsun SU would support a Crown Turbo Kit to about 12psi. Using a Jaguar 2" having a 0.125" jet would support the kit to well over 20psi. Do the math on the horsepower.

 

The thing is the fuel pumps are weak, and when yo ustart sucking hard on CV carbs the float bowl level drops. Put the site gauge into the float bowl in the little hex plug provided and do a dyno run---watch what happens to your float level.

 

Realize that a high pressure pump (something that can push 20psi) and a backpressure style fuel system can really help with keeping your float bowl level proper under hard load and high rpms.

 

I see what you mean by "not really true". Basically the fuel flow doesnt support the nozzle size. I currently run 5psi with a carter pump in front and a Hitachi knock off by the tank. I have a gauge and pressure regulator in the system as well. I might try upping the pressure on the system with what I have. I think I can get 8-10 psi out of the front pump. Might be an interesting experiment on the dyno. I dont have a sight glass for the carbs. In the past my best efforts were to kill the engine during a problem, pull the float bowl top off, and inspect the level. Thats actually why I have a fuel pump in the engine bay now and the stock mechanical one has been deleted.

 

Nissan came out with the flat tops because the mandate for idle emissions. it separated the idle from the main system in order to run a proper power taper on the main system, and put a finely controlled metering block in for use at idle. The power valve was supposed to work for interim 'accelerator pump substitution' by richening the transition so you didn't have a flat spot off-idle and bog. If the power valve takes a dump, you go rich. Really you can retaper the needle at the transition point to go rich when coming off the idle circuit, and still have proper AFR up to the top of the RPM range if you run a flat top.

 

But I digress...

 

That was what I was getting at with my statement it just came out without precision. Ive been temped many times to just slap those suckers on my cars. A sizable amount of the zcar community would probably have me tared, feathered, and promptly hung for that one though.

 

 

Ray, you are SO CLOSE with this statement! You have just misphrased it slightly.

 

You realize in your statement that you have a "Pertronix Pointless Ignition" Which really I take to mean "Pertronix Pointelss Coverted Distributor"...

 

Really anybody using a Converted Pointless Distributor is close to realizing a Distributor is Pointless.

 

 

They are not the same thing...

 

You have a Pointless Distributor, now realize a Distributor is Pointless.

 

COP my man...COP!

 

 

lol, Id love to be using a crank trigger, on a Ford EDIS system. Its not COP, but its close enough for me. Ive been setting up an EDIS system on my 68 2000 with Megasquirt so I would already have a good handle on how to build it. Its going slow on the 2000 and Im several years into messing with it. Its way on the back burner at this point. I do love being able to play with the timing on my 260Z as well. Im running an Apexi Power Fuel Controller and tinkering with timing maps on my netbook is just to easy with that setup! Advance the timing until you ping then pull back(I have a data-logger hooked up too). Its kinda like cheating with the netbook compared to the antiquated L24 in stock form. Ive totally missed out on the art of building and tuning a timing curve in this way though. I could not build a curve from a blank map as of now. Anyone can plug numbers into a map and most can watch for detonation.

I ran into one of these 6 months ago and was highly tempted to purchase it just so I could try and teach myself. Some of these things are becoming lost arts and I love old cars so I make it a point to learn what I can. You know just for the fun of learning the basics.

 

 

It was out of my price range at $150-$200 though Im sure thats what they can go for, I was just ultra broke at the time.

[madkaw]

I guess i'm a little confused(but that doesn't take much), are you building this motor now, or is it running now? I am curious too that you put bigger valves in and didn't mention about notching the bores.(you have to do that). Unshrouding will be beneficial too!

I am also "building" a L24, vs the L28, just because that is what i started with. I also have a lean condition on top-end, but i am very happy all around. Just now installing my G3 Innovate, so I will be able to tell more later. I did dyno my l24(there is a thread on this) and my car went way lean WOT with SM needles and the floats adjusted to spec. My timing is 20 static-36 full in with no advance-which I don't run. Very torquey, but again the top end is a little weak. I believe it is fuel delivery, but to be verified by my wideband.

I ran 150HP and ran out of gas over 5100rpm, so the mighty L24 can put out. I am also running true duals 50mm, which doesn't seem too big to loose low-end, but getting the most HP out of it will be interesting.

[rayaapp2]

I guess i'm a little confused(but that doesn't take much), are you building this motor now, or is it running now? I am curious too that you put bigger valves in and didn't mention about notching the bores.(you have to do that). Unshrouding will be beneficial too!

I am also "building" a L24, vs the L28, just because that is what i started with. I also have a lean condition on top-end, but i am very happy all around. Just now installing my G3 Innovate, so I will be able to tell more later. I did dyno my l24(there is a thread on this) and my car went way lean WOT with SM needles and the floats adjusted to spec. My timing is 20 static-36 full in with no advance-which I don't run. Very torquey, but again the top end is a little weak. I believe it is fuel delivery, but to be verified by my wideband.

I ran 150HP and ran out of gas over 5100rpm, so the mighty L24 can put out. I am also running true duals 50mm, which doesn't seem too big to loose low-end, but getting the most HP out of it will be interesting.

 

 

Engine is currently running and in the car. I like to plan things out before I undertake them, so until I have a good plan laid out it can stay running and sitting in my garage. It took me 5 years to plan out, 3 months to acquire parts, and about a week to build my rb25det 260z.

 

I agree, the big hulabaloo about eyebrowing the bores is not a 'NOT'. The heads WILL work, but it depends on how the dowels and head are positioned on the block wether or not the valves tag the tops of the bores or not. I have even seen early L24 engines with big-valve N42 heads on them where the valves 'self clearanced' against the block at original crankover, and then ran tens of thousands of miles before anyone found out the valves were (at one time) interfering with the block.

 

It's more of a 'should' eyebrow the block statement, rather than a positive declarative sentence structure.... Always check interferences before assembly and determine what needs clearancing and what does not. Some may need it, some may not. Do it and you know you won't have a problem.

 

The valves I installed didnt require notching of the cylinder bores. I reassembled everything myself. I did it about 8 months ago, but cannot remember much about what was measured. The bores were stock or close to stock, but there wasnt a need to notch the bores. These valves weren't the biggest ones available though. There is a larger set for L28 out there that is pretty common. I had a used set of those around to compare with. I also had a few sets from an E30, E31, late E88, P90(the big ones), and they were all different sizes. There was enough clearance when I measured it out. Now that I think about it, The valves may have been for the L26 N42 head? IDK just guessing. I bought them as new old stock and wish I could find part numbers. They are bigger than the large E88 stuff and smaller than the P90 ones. Ive seen so many L series engines that I cannot recall if they were already notched or not, I just know that I recall checking for fitment and clearance before I slapped it on.

 

Id be happy with 150hp at the wheels, but Id like to see more. Id be ecstatic with 200+rwhp. Torque usually isnt an issue with the L6, but as much as I can possibly make of that stuff would be good too. Thus far the 240Z is the slowest car I own. Well except for the 2000 Roadster(It doesnt count because it isnt running). I enjoy a good freeway merging... as opposed to a good freeway smashing me to bits, amongst other things. Actually my goal is more of a: learn as much as I can and see how well I can apply it deal.

 

I love my LC-1 on my 260Z, HOWEVER I have noticed it does not read correctly. Even after calibrating it, it always seems off a little bit, and not always the same amount Its usually within 1 afr(what ever increments that is) of the true reading. I have connected the car to other wide bands and seen a slight variation. On top of this I have spoken with others that run the Innovate wide bands and they all have the same problem. Its good for a basic tunes, but dont let it be your be all tell all for tuning, back up your data with a second calibrated wideband when tuning. my 2 cents on that.

Edited December 6, 2010 by rayaapp2

[30 ounce]

What oil are you running in the carb dampers? I use 5w motorcycle shock oil or auto transmission fluid. I experimented with other wieghts and found that 15w and above made performance above 2500 rpm's sluggish just as you discribed.

 

Although SU carbs have thier limitations they are capable of 250-300 hp. Ask Dave Rebello.

[rayaapp2]

What oil are you running in the carb dampers? I use 5w motorcycle shock oil or auto transmission fluid. I experimented with other wieghts and found that 15w and above made performance above 2500 rpm's sluggish just as you discribed.

 

Although SU carbs have thier limitations they are capable of 250-300 hp. Ask Dave Rebello.

 

my own quote:

"Damper Oil only affects incoming acceleration of air not how far the slide will open or static flow rates... The spring tension on the top of the slider may affect a steady amount of air, but Im unsure as to what extent. Definitely not oil. I did have to change the oil from ATF to 20 weight to get the richer mixture on acceleration I wanted."

 

I opted for thicker oil after finding my "transition" to be leaned out. Due to the thicker oil I have had less consumption of that oil as well.

 

As far as power support goes, I can see that if your talking about the same thing as Tony. Potential is there, but in stock form at stock specs Im afraid its inadequate for even a stock L24. It requires work to support the theoretical flow of both the main jet and venturi. Thats why Tony said "This is not really true" in response to my post and not that my statement was outright wrong.

 

It appears I posted this back in June when it was on the dyno.

SU carb dyno tuning CLICKY

I should have peeked at this first as it has all my SU carb tuning AFR Data. Have a look.

 

And for Tony:

A couple of more months Ray, and you will start thinking of ways to convert those SU's into Megasquirt Powered TBI!

 

I know I did...

 

NOPE LOL Im not that smart yet... I want to upgrade to the bigger headache, Mikunis!

If these weren't so darn spendy I would have

All out of my budget for the short term. Someday... when I can blow money at will... Until then a cheap used set of Mikuni's are all that's in the budget.

Edited December 5, 2010 by rayaapp2

[ktm]

I love my LC-1 on my 260Z, HOWEVER I have noticed it does not read correctly. Even after calibrating it, it always seems off a little bit, and not always the same amount Its usually within 1 afr(what ever increments that is) of the true reading. I have connected the car to other wide bands and seen a slight variation. On top of this I have spoken with others that run the Innovate wide bands and they all have the same problem. Its good for a basic tunes, but dont let it be your be all tell all for tuning, back up your data with a second calibrated wideband when tuning. my 2 cents on that.

 

Sounds like a ground offset issue and not necessarily a gauge issue. If it were truly a gauge issue and a pervasive problem, the 'net would be awash in whining about blown motors.

[Leon]

What condition are your carbs in? Old SUs tend to leak around the throttle shaft when the bushings get worn. This may be causing a vacuum leak which leads to the lean mixture. It may be a small leak, but it will affect the mixture. Check by spraying starting fluid around the carbs. If you hear any changes in sound as you spray over the throttle bushings then there is definitely a leak.

 

My thought is if you have a properly tuned, good set of SUs (e.g. ZTherapy rebuilds) then you should be good to go.

[rayaapp2]

Ive gone through the carbs. They are in good working order. They dont leak from the typical wear areas. Im the local guy everyone calls to set these carbs up. My typical fix for the lean problem is to run a vacuum switch from manifold vacuum and use it to actuate a metered vacuum leak to the balance tube at idle/decel(high vacuum conditions) to lean out the mixture so you can pull the main jet down more and fatten up the mixture without fowling the plugs at idle.(An idea I borrowed from an old carb tinkerer) That still leaves you with a lean WOT condition though, which is what the main problem we're discussing here. Besides a small vacuum leak around the throttle shafts is minuscule at WOT. It would barely if at all affect the AFR. Ive played with this trick without the vacuum switch on the dyno and it didnt skew AFR at WOT dyno-jet pulls. It would have to be a very obvious vacuum leak to mess with the mixture as far as I can tell. The metered vacuum leaks I made most likely flowed more than a leaky throttle shaft.

 

From what I can tell my numbers are typical of SU carbs. Anyway I do not plan on continuing to use the SU carbs. Mikuni Side drafts are on the list.

[rayaapp2]

opps double post

 

Anyone want to critique my build idea?

Edited December 5, 2010 by rayaapp2

[rayaapp2]

Ray, you are SO CLOSE with this statement! You have just misphrased it slightly.

 

You realize in your statement that you have a "Pertronix Pointless Ignition" Which really I take to mean "Pertronix Pointelss Coverted Distributor"...

 

Really anybody using a Converted Pointless Distributor is close to realizing a Distributor is Pointless.

 

 

They are not the same thing...

 

You have a Pointless Distributor, now realize a Distributor is Pointless.

 

COP my man...COP!

 

Alright Tony, You got me here. Its in my best interest to go distributorless. Why dial in a cam with precision if you dont follow up with precise ignition timing to take advantage of said dialed in cam... Then my only weak link is timing chain tensioners... which Im not going to spend $800 or whatever dollars on the Kameari tension... so ?

What are some options out there for stand alone ignition? I know about the EDIS system, I have heard of the Electromotive ignition stuff(I really want to know more here, but their website SUCKS!), and that is about it.

 

Im open to crank fire ignitions through the stock cap and rotor... setup not unlike the 81 turbo cars. It retains a stock look that I like.

Edited December 6, 2010 by rayaapp2