triple 40 webers...best head to run with?

[johnc]

I'll be the skeptic. I think you need to check your ignition system (particularly the coil and the trigger) and your tachometer. Secondly, install a good external shop tachometer and then see what rpms your motor is turning.

 

If all the above checks out, then I'll be a believer. Until then, I seriously doubt and stock SU carb'd L6 will hit 9,000 rpm - at least not more than once in its short life.

[yo2001]

I'm sure the there is a way to sleeve the block with titanium. But if the motor is turning that high of rpm, you be going through some piston rings all the time. L6 crank is only good for like 8000rpm if you are lucky. You really need a full counter crank to do that kind of rpm. L4 can because the shorter crank and some are even full countered crank. 280deg cam isn't big enough to turn that high and you'll need like 12:1 compression motor to keep the compression high enough. Still, your motor sounds like a good motor. Destroked L29 will need a longer rods like 140mm FJ20DET rods. those are hard to come by.

[Guest DATTO]

well ill try to write as much detail as i can, my friend in los angeles built the car about 3-4 years back...the original setup was an e31 head port and polished, hks 280 dur mild cam, nismo valve train, l28 valves, the block was heat treated, the crank was shot peened, knife edge cut, counter balanced/counter weighted for a quicker rev, titanium sleeve i was told to make the car from blowing and lasting longer with the higher revs and it was an n42 block,100 overbore, nismo 2.9L dished pistons, on the compression...it got 230+ psi, hks lightflywheel, 6-1 headers, crane hi-6 ignition with ps92 coil, euro distributor, stock SU carbs with k@n filters, nismo close ratio tranny, balanced and bluprinted and thats what i can remember so far about my motor...i had so many people not beliving the high 9k rpms shifts til i showed them and took em for a ride...i had my fren come over with his CBR1000 and i told him to rev his motor up to 9K and we did it at the same time and my car hit 9K rpms faster than his bike...then i took him for a ride and showed him how it gets up in first gear...he never seen anything rise up so quick...i went through 1st and 2nd so fast revving the car to 9K shifts. my car would rev to 9K in a sec and drop down to idle in almost the same time. my car almost sounded like a motorcyle when revving..quick and responsive. if i ever find my friends best frined who built the motor, ill add a post about the motor and try to get all your questions answered. my friend is in hawaii at the moment but as soon as i can sontact him, ill try to ask him to call ben who built my motor... as for the triple 40 carbs, the deal didnt fall through for me and i couldnt get the carbs...kinda sad but i just met a cool guy who works on many cars, builds turbo z's...right now hes trying to figure out how to put a RB26dett head on an L-series block...he has already got a chevy block and mated porsche heads on it and he says it works fine. so he really wants to build my motor to get about 320-340hp at the wheels with the stock t3 turbo with 13psi of boost, the best he has ever got a stock turbo motor with his cylinder head port job, 300zx maf sensor, 300zx computer, and ported intake and turbo manifold with 240sx throttle body and stock injectors was 314HP at the wheels, i forgot what psi he ran to get those numbers...so hopefully with my turbo parts i can get the 320-340hp range...ill keep you all posted on progess....take it easy all!

[DAW]

Lots of diatribe in this thread.

 

RE: the original post re best head for high performance na L6...I didn't see any comments or response to my selection of the L6 Maxima N47 head as perhaps the highest potential na L6 head with some slight modifications (nothing as extensive as shaving 0.80").

 

The L6 is basically a "plus 2 cyl" version of the L4 (the LD28 is a "plus 2 cyl" version of the L4B)

and the US market L20B U67 head represents the L28 N42/N47 head; there is a closed chamber head for L20B truck engines (W53 sq port, W58 rnd port) that is a smaller volume chamber than the U67 and provides better performance with less tendency to ping than does the U67 at the same c.r. The W heads can run a smaller chamber than the P79/P90 heads because there is less displacement per cylinder (smaller bore, deeper dished pistons) than the P79 L28E/ P90 L28ET, and there is no corresponding L4 head to the P79/P90 (shorter-valved/raised roof) head.

 

The biggest oversight in L6 performance head selection is the Maxima L24 head. It is the equivelent of the W58 L20B head and this configuration is not otherwise available for the L6 (but would be on a factory 10.5:1 L6). DAW

[Lockjaw]

Hey TimZ, don't forget about head saver shims. I used them in my application. Also, you can "adjust" the cam timing via the timing gear to make up for the retardation. One of the heads was uncut on a 3 liter with rolled domes, and it was the only head we tried on that engine that made it run right.

 

My friends engine though with 110 cut did not use shims, and I don't know what he did to it, but it was strong. He took slack out of the chain by adjusting the guide rails.

[TimZ]

I didn't forget about the cam shims - as I recall, you said all you did was cut the head and swap cams. In this case, the cam timing is different between the two.

 

And I also know that you can fix this problem, if you know it exists, but you gave no indication that this was the case. Also, there are many fine details that can have a significant effect on cam timing - enough that you can't know if you have an apples to apples comparison without actually degreeing the cam.

 

The thickness of the head has a huge impact on cam timing (at least when we are talking about differences on the order of 0.100"), although this one is fairly easy to notice via the timing marks. However, there are many other factors that effect the cam timing that don't show up on the timing marks. Basically, anything that effects the position of the wipe pattern on the rocker will effect the actual valve opening timing. Cam base circle, lash pad thickness, valve length, valve installed height, rocker arm resurfacing to name a few - also notice that there is no guarantee that any of these things will be exactly the same from valve to valve on the same head. And since all of these effects take place "after" the cam sprocket, they will not show up on the timing marks. You can only detect this by degreeing the cam.

 

Being able to assemble a head and have it run without destroying itself does not necessarily mean that you know what you've got.

[Bob_H]

Alright, this is going to be fun. I feel a little better being backed up on my thoughts. However, some more responses:

 

JohnC said:

I'll be the skeptic.

Thank's John. I am skeptical w/o actually seeing it though, for my above mentioned reasons. I bruised too many ego's with my full frontal attack, so I softened the blow for that one. Second, Mine can hit 9k, for a brief glorious second when not in gear. I'm not about to try it either. 7k is my self imposted limit, mainly b/c of the stroker crank and pistons speeds. But this subject is dead already. I would be skeptical of the igntion as well, but you already pulled the head, so the discussion is moot.

Next.

 

yo2001:

I'm sure the there is a way to sleeve the block with titanium.

I'm sure there is as well, but why? Titanium is just not used in a metal on metal contact point. They don't use it in F1, so I don't see why it would be used for high rpm in this application. Of course, they don't use nickel iron blocks in F1 either! I seriously doubt it is a titanium liner. If anything, it is titanium parts in the valvetrain such as retainers.

 

Next.

 

DAW:

Lots of diatribe in this thread.

HA! yup.

I didn't see any comments or response to my selection of the L6 Maxima N47 head as perhaps the highest potential na L6 head with some slight modifications (nothing as extensive as shaving 0.80").

Actually, we were ignoring you! I'll respond. First, I don't think it is the "best" head for a 2.8. I think it is the "best" head for a 2.4 or 2.6 motor. The rather extensive work required to get decent airflow through that head lowers its value to the "backyard" enthusiast, i.e. one w/o the knowledge to port and unshroud and such. Either the intake or the exhaust,(I forget off hand), has to be increased in size to match the stock valve sizes in the N series heads,(Z heads). Second, the combustion chamber has been measured to be in the 39-40cc range for that head. With a stock gasket, you are talking 10.7:1 with flat tops. When you switch to dished pistons,(depending on which ones), you lose some of the advantage of that "quench" or "squish" design of the chamber, as it won't push that mixture tumbling towards the center as the piston approaches TDC. However, with mods to unshroud the valves,(stock Z size valves), and some minor bowl work, it is a great head for a 2.8 motor. And with those chamber mods to unshroud the intake, you increase the chamber volume, and approach the more resonable CR. However, how accurate can you be to ensure each chamber is close to the same size? It is for those reasons that I don't think it is the best plug and play head. But it does offer great potential. I don't think it is overlooked, but rather, people shy away from the mods it does require to work on a 2.8L. But as a bolt on to a 2.4L, wow, that would be great!

 

edit: You mentioned "not as extensive as shaving .080". I think monkeying with the chamber,(unshrouding) in any way is "extensive", and much more so than shaving the head. But others may not think so. /edit

 

Next.

 

Back and forth btw Tim and Lockjaw.....

 

Personal note/experience on shaved head and retarted timing. In my P-90 what was shaved about 20 thou, the number one hole retarted the timing and fixing that alone,(going to the second hole), made almost a 15 hp difference. And about 5-10 hp throughout the range. So it is not insignificant,(and mine is a street motor, not a "race" motor). And degreeing a cam shows more than it is what the manafacturer said it is and where it is. That last part is huge. Degreeing a cam will show you if it is retarded or not. See above power claim with retarded camshaft. On a higher powered car than mine, the effect can be larger,(turbo/race). And on a head that is shaved more, it might take to the third hole to get it where the manafacturer said it should be. As a reference, my head is shaved about .35 thou right now and the cam had to be in the second hole to get it degreed properly,(btw, hydraulic heads are a PITA to degree, the dang lifters bleed down after a few min!) When the cam timing is off, so is your ignition. I chased that on my last re-assemble of the head. The camshaft was retarded on link in that case, which wrecked havoc on the timing and power. One link can be similar to shaving the head a significant amount and retarding the camshaft.

I offer that up as a reference. I'm not stepping in the middle of this one. It is doing exactly what I wanted, good discussion back and forth.

-Bob

resident jackass

[TimZ]

Originally posted by Lockjaw:

I don't see where cam timing would have that huge a difference anyway. It is only going to be as precise as the tolerances on all the components involved, so theoretically, it would be next to impossible to duplicate one head to another since there are so many variables. All degreeing is going to do is tell you where it is, and if the cam is ground as the manufacturer claims.

I would contend that the cam timing could easily make a bigger difference than the head design. This, of course depends on a lot of things, but that was EXACTLY my point. There were way too many uncontrolled variables in your experiment to make any conclusions as to which series head is 'best'. Even the anecdote about four different heads consistently being better - if they were all shaved, then they all had modified cam timing. Who is to say that the N-series head wouldn't have made more power with the same cam timing?

 

BTW, the head saver shims can correct the timing shift due to the chain slack, but they also raise the cam centerline relative to the valves, which, you guessed it, effects the cam timing.

 

Just to be clear on this - nobody was saying that there was anything wrong or inferior about the P-series heads - obviously several people have had very good results with them.

 

What I and others took issue with was the blanket statement that the P-series is always better, followed by some supporting arguments that do not hold water under close scrutiny. Sorry, but that is the way I see it.

 

Bob - my experience with cam timing changes were similar to yours - thanks for mentioning it. One thing, though - I'm pretty sure that the distributor drive is taken directly off the crankshaft gear on the L-series (still a 2:1 ratio though, obviously). So, the cam timing should be independent of the ignition timing in this case. I'm speaking from memory here, so if I'm wrong, somebody please correct me...

[Bob_H]

blah, blah...So, the cam timing should be independent of the ignition timing in this case.

more blah

Well, actually my distributor is driven directly from the front tires. So it is all moot for me. I am kidding. (he deadpans)

In reference to your comment, yes, ignition timing is independent, however, comma... With the valve even timing significantly off,(as was mine), sparking at xx degrees before TDC assumed I had a certain amount of compression built up, which I had a different amount. So in my case, on the chassis dyno, it turned out to cost me nearly 20 hp till I could get it correct. That was a combination of BOTH ignition timing being off, (I had it off one tooth), and the cam timing being off. Not a good place to start. My first pull with it all screwed up was 138 hp. (this motor had already proved itself at 170 before, so it was my screwed up install of the cam) Ended up with 178. Got it up to about 160 by fixing the timing. Then got up to 178 with the camshaft correctly degreed,(was off the aformentioned one link). That was the point I found out heat was a major problem and that is my next assignment, a heat shield. That is what timing and retarded camshafts can get you. One last point on the ignition timing related to the camshaft timing. I don't have a dial gauge to get exact TDC, so I was putting it pretty close, then looking at the camshaft to see where the lobes were. Oops. Didn't exactly help.

Ironically, on some of the chassis dyno pulls,(not talking about the above set, but my first set when I first built the engine), with the cam on the #1 hole, I made the most torque down low. When I advanced it to #2, more power, and better overall torque/power. So it would lead me to believe that a retarded cam could actually feel faster than a correctly set one, b/c of the increased power down low. But that is all conjecture, not actual experience. I never drove it like that.

-Bob

[TimZ]

Originally posted by Bob H:

blah, blah, smartass comment, blah

With the valve even timing significantly off,(as was mine), sparking at xx degrees before TDC assumed I had a certain amount of compression built up, which I had a different amount.

Yep - I agree with this.

 

When I advanced it to #2, more power, and better overall torque/power. So it would lead me to believe that a retarded cam could actually feel faster than a correctly set one, b/c of the increased power down low. But that is all conjecture, not actual experience. I never drove it like that.

-Bob

Some of this most likely depends on the cam design, and definitely on the other variables previously mentinoed, but my experience has been that retarding the cam timing should move the torque peak to a higher rpm, not lower. The optimum cam timing setting (again, depends on lots o' stuff) can be fairly peaky (i.e., power falls off quickly on either side), so it's quite convievable that when you advanced the timing to the #2 hole, you brough it back into the 'good' range. Maybe. Who knows?

 

One final illustrative anecdote...

I did try a few different cam designs a while back. I had my original Isky cam dialed in at zero degrees to start with.

 

New Cam Number 1 was a regrind that should have been a bit more aggressive. Ran like ass when I had it installed to the same timing settings (on the sprocket only) as the Isky. After some experimentation, I found that this cam needed to be retarded by 6 degrees in order to run equivalently (not better, BTW) to the Isky.

 

New Cam Number 2 was a regrind that should have been more aggressive than New Cam Number 1. It also had a different base circle than New Cam Number 1. New Cam Number Two ran like ass when I had it installed to the same timing settings (on the sprocket) as the Isky. This cam, however, needed 6 degrees of advance to run almost as good as the Isky.

 

At this point I put the Isky back in, and never looked back. Anyway, in both of these examples, the cam timing marks appeared identical to the install with the Isky, which had been properly dialed in. The main thing here was the base circles were different enough to cause an apparent 12 degrees(!) of timing offset between them. Or maybe the cam grinder was drunk, I dunno. Either way there was a ~12 degree discrepancy between the two cams that did not show on the timing marks at all.

 

This, BTW, was how I learned all this stuff about cam timing and head setup...

[Lockjaw]

I don't see where cam timing would have that huge a difference anyway. It is only going to be as precise as the tolerances on all the components involved, so theoretically, it would be next to impossible to duplicate one head to another since there are so many variables. All degreeing is going to do is tell you where it is, and if the cam is ground as the manufacturer claims.

 

Seriously, we did not go to great lengths to make sure the timing was exact. Some of us (me) were more precise than others. I at least went to the trouble of shimming my cam towers, and measuring the differences in base circle, and matching up a lash pad. I always lined everything up per the spec's, but never went as far as to find true TDC or anything like that.

 

On a turbo engine, or a race engine I could see going to that level, but on a street engine that never saw a dyno, don't think it was worth the effort.

 

That sort of thing is just not my area. I mean its not that I don't think that there is power to be made doing something like that, I am sure there is. I don't have the equipment, and even if I did, I don't have the engineering back ground to take advantage of the information.

 

Maybe my info is a little oversimplified, but we literally took the cam, springs, retainers, lashpads, rocker arms ect, and transferred them from one head to the other. Retained the same sprocket. If the head had shims, of course we adjusted lash pad thickness to accomodate. Even if it wasnt the most scientific test, the fact that 4 engines ran better with a P79 than they ran with "other" heads when almost all of the components were transferred from head to head kind of tend to indicate the P79 might be a little better choice, IMHO.

 

Anyway, don't think I am trying to say what you are talking about doesn't have merit. I think it does.

[Lockjaw]

Sounds like I need to spend some time playing around with a degree wheel next time. HEHE.

 

SOunds like you got ahold of some fly by night cam grinders Tim.

 

We were using billet cams in our messing around, with the exception of one car, which ran the electromotive L9 grind. It was a sweet cam.

[Guest Anonymous]

Hey!

I'm a first timer on this list. It looks like a source of alot of good info.

 

All this discussion about heads has left me at a quandry though. I plan to build a L28 flat top engine, but still can't decide on which head to use. (I have a F54 turbo short block but need the flat pistons)

I have a P90, P79, and a N42. I tend to agree with both sides. I think the chamber design is better on the P series, but the ease of higher compression with the N42 is also very appealing. This will be my first engine build, so I'm not very comfortable dealing with valve train geometry. A high compression P90/P79 with a good cam and corrected geometry would be SWEET. Oh yeah, I almost forgot about the $$$ though. I can't afford sinking alot of money into having a head totally modified either. I'm trying to build an engine myself without spending a wad of $$$.

 

Oh well, I'll just keep reading the info. Maybe by the time I actually build, I'll have made up my mind.

 

ps: I'm open to advice, etc.

[Lockjaw]

Is there a post from DAW on here about the maxima head? If so, you could go that route and get the compression without having to mess with the valve train geometry. I think it has smaller intake valves, so you would have to have that issue taken care of, but I doubt having 6 larger valve seats put in would be to bad. You should get a 3 angle valve job done anyway.

 

The maxima head has the P series combustion chamber, which is the benefit of going that route.

 

Since you have a turbo engine, why not go that route instead? You would be faster.

[Guest Anonymous]

Maxima head? I figured those were hard to find. Wouldn't I have to replace the valves?

 

Anyway, about the turbo swap. I guess since I already have a 280zx Turbo, and my lack of knowledge in what it would take to convert a 240 to FI, I dismissed that idea. Oh yeah, also I spent a wad of $$$ on a set of Ztherapy SUs when I bought the car. It had been in storage for 8 years and the carbs were crusty.

 

Lockjaw, are you in B'ham? I'm from Tuscaloosa, and periodically travel back there. If you've done a conversion, I'd still like to see it.

[DAW]

The N42 works fine except it does tend to ping more than a P79/P90/Maxima N47 type chamber. N42 is a quick route to higher compression/performance but be prepared to use octane boosters and deal with more critical, less forgiving tuning parameters (timing, mixture).

 

If you have a flat-top L28 and a P90 and access to a turbo setup, you could build a low-pressure turbo engine that would be a killer autocross car because the relatively high static c.r. (8.6:1) would give off-boost responsiveness and the turbo would provide a huge increase (intercool it) in power over a na engine of the same c.r. You might need to limit boost to 6lbs or so to start with such an engine. Putting a factory L28ET turbo setup into an early Z isn't really very difficult, just keep all the donor harnesses intact. DAW

[Lockjaw]

Boozer I am on the Gadsden side of Bham, in between springville and trussville.

 

My car is a 280zx right now, but the conversion is not to tough. I will likely end up with the turbo engine in a smaller Z car, but I am not set on keeping the 260 I have right now. So until I decide on that, it stays in the ZX.

 

I also converted an NA Zx to turbo, and it was a piece of cake to do that one. I still have the little harness I fabbed up to connect the ZXT harness to the ZX hardness over by the battery.

 

Oh and the P79 is on the 260 engine, but I have not gotten it to stay running long enough to tell very much about it, other than that the cam is pretty big. I actually think I could have gone with a thicker lash pad than I went with, but until I get a muffler on the car, I can't tell if the valvetrain is quiet or not. If it has decent compression, it should be pretty stout. I always liked the 260 engine too.

[DAW]

Lockjaw, I might be telling you something you already know, but re bigger lash pads, if you milled the P79 and shimmed the towers, one way to avoid buying thicker lash pads is to install the valves from an N42/N47 head as they are a bit longer than the P79/P90 valves, so you can take up the slack with the longer valve stem instead of a thicker lash pad and accomplish the same thing. I think this trick could work on a reground replacement cam also with its smaller base circle. DAW

[yo2001]

Originally posted by DAW:

Lockjaw, I might be telling you something you already know, but re bigger lash pads, if you milled the P79 and shimmed the towers, one way to avoid buying thicker lash pads is to install the valves from an N42/N47 head as they are a bit longer than the P79/P90 valves, so you can take up the slack with the longer valve stem instead of a thicker lash pad and accomplish the same thing. I think this trick could work on a reground replacement cam also with its smaller base circle. DAW

Also, don't forget to add more shims under the valve springs. Without them, you'll wacked the seat pressure.

[DAW]

I don't think that's the case with the valve springs. The installed ht is the same. The length difference is due to changes below the surface of the valve spring seat, i.e., the roof of the chamber is different. The configuration up top is the same. DAW