inline6

May 19, 2015

Found another zcar.com thread with info about clutch pedal height that is interesting - Tony again... go figure. The FSM says to use the threaded rod on the clutch master cylinder to set the clutch pedal to the correct height off the floor. But Tony says (in post #10):

"Pedal height is pretty much irrespective of the adjustment---the bumper on the screw should adjust that...the clevis simply sets where the piston is within the cylinder itself."

Now, that is interesting. As I stated above, I set the clutch pedal height at 8" by threading the clutch master cyl. threaded rod in until the pedal was 8" off the floor. I then set the rubber bumper on the screw so it was snug against the clutch pedal arm. Setting it in this fashion made it so I could not shift into any gear with the engine on.

Separately, when I bolted the slave cyl. to the transmission, I had to compress the slave cyl. rod. Fully compressed, the slave will bolt to the tranny with no issues. The piston in the slave is pretty well bottomed out.

Based on what Tony said, I decided to test something.

I loosened the lock nut on the rubber stopper and backed it as far away from the pedal as possible. Then I loosened the lock nut on the clutch master cyl. rod and screwed that rod out of the clevis until the pedal was again in the position where the clutch became functional. My clutch pedal is now at like more than 9 inches off the floor - more than an inch higher than the brake pedal. Then... I again set the rubber bumper to hold the clutch pedal at 8" off the floor. But, as I did so I watched the slave cylinder. And, as I moved the clutch pedal down from 9+ inches to 8", I saw that the slave cylinder rod moved, which "pre-loaded" the throw out bearing on the PP spring fingers.

So... given what Tony said: "Pedal height is pretty much irrespective of the adjustment---the bumper on the screw should adjust that...the clevis simply sets where the piston is within the cylinder itself", and what I see happening on my car from the aforementioned steps that I took, then what gives?

My conclusion is that the only way he could be right is if one additional thing is done in my scenario with my car. If it is true that pedal height can be irrespective of the adjustment... that I can set that simply with the rubber bumper on the screw... then the only way to alleviate the slave cylinder movement I am experiencing is if I crack open the bleed circuit after I have set the clutch for proper operation with the clutch master cylinder threaded rod. But won't that just return the slave rod back to the original start position and won't I lose all of that travel (that I had)?

I'll give it a shot, but seriously, I am coming to the conclusion that the 5/8" MC and 3/4" slave don't have the stroke to get this job done.

May 17, 2015

I just verified that stock 1983 Datsun 280ZX non-turbo has a 5/8" clutch master and 3/4" slave... same as what I have now.

Just found this post (#8 in thread) from Tony where he points out that there is a common problem with clutch master cylinders that have rods that are too short. He mentions aftermarket... I don't think mine is aftermarket because it is a Nabco, so maybe it isn't just an aftermarket issue.

His post #9 is also interesting... I have been wondering why my poor shifting seemed to have gotten worse recently when it had been workable for many years. The new clutch disc actually makes the problem worse because the fingers in the spring diaphragm actually move away from the throw out bearing a bit more. As a clutch disc wears the finger move closer to the T/O bearing.

And finally, in that post, the original poster (OP) states that they solved their problem with a slave from a 1988 Pathfinder.

I looked around for some images and see that the Luk one at RockAuto has numbers on the side like the original equipment (OE) ones. It looks to me like it says 11/16. Ok, now I see some of the descriptions of the others say 11/16". Same amount of volume of fluid being forced (MC) into a smaller container (slave) would cause the slave piston to move further... and man are those Pathfinder slaves cheap!

May 17, 2015

I tend to be rather wordy, so I am editing and putting the questions up front:

With a 240 mm clutch upgrade and a late style ZX gearbox, are the stock clutch master cylinder and stock slave cylinder suitable to achieve enough travel for full disengagement of the clutch disc, without pre-loading the throw out bearing?
If so, can suitable travel be achieved with the clutch pedal in the stock position - 8" from the floor?
If not, has anyone focused on this issue and come up with a combination of MC and Slave that does work with the clutch pedal at 8"?

(End edit)

I've never been happy with my clutch since I switched to a late style 280ZX 5 speed eons ago. I messed with pedal height and got it to work ok way back then and drove it for years without any real issues. However, with my new engine which revs higher, I am having a much harder time getting it out of gear and getting it into gear at high revs.

Today, I tried setting the clutch pedal height back to stock per the FSM. I set it at 8 inches from the carpet on the floor to the front surface of the rubber foot pad by undoing the lock not on threaded M/C rod and screwing the rod into the clevis more to lower the pedal height. After doing this, I can no longer get the car to shift into gear with the engine running. Clearly the clutch pressure plate spring fingers are not being engaged enough to release the clutch disc.

The clutch M/C and slave have been checked for leakage and there is none. System has been bled thoroughly and no air bubbles are coming out. I have visually verified that the rod on the slave is moving the clutch fork. Additionally, I took the slave off the tranny, took out the clutch fork boot, and shined a light up inside the tranny. I tried moving the fork by hand back and forth. In it's natural static position, it seems to me that the throw-out bearing is resting on the pressure plate spring fingers. I can't force the fork (pushing toward back of car) and achieve any movement at all. I can, by putting light force from the back toward the front, get the fork to move some in that direction. That obviously pulls the throw-out bearing/collar away from the pressure plate.

My clutch master cylinder is a 5/8 Nabco. It is stock 240z as far as I can tell. My slave cylinder is 3/4" Nabco. Are these suitable, or no?

The disc and PP have about 1500 miles on them. They are ClutchMasters 240mm units which are mounted on a Fidanza aluminum flywheel.

Through my searching I am aware that there are different T/O bearing collars and that I need to have a stacked height of 92 mm from the flywheel surface to the "wings" on the throw-out collar that the clutch fork rubs against.

Is there any way to measure this without take the trans out of the car?

Clearly, something isn't optimal. If I raise the clutch pedal about another inch or so higher than the brake pedal by screwing the threaded rod in the clutch M/C out, I can get a functional clutch. As I said before, however, 7000 rpm shifts pretty much don't work - the shift lever resists my efforts to pull out of first... and I can't get into second until the revs drop below 6000. Also, the reverse idler gear is not quite stopped... it is causing a bit of grinding when shifting into reverse even with the clutch pedal firmly against the pedal stop.

May 13, 2015

Like TonyD said. When tuning only change one thing at a time. Some of those lists you showed are main, air, pump, and pilot in one step! Wow you Will never tune doing that.

When I switched from Webers to Mikunis I talked to Todd W. Sent him my engine, cam specs etc because my engine was more than the guy I got them from.

I have a 2.9L, p+p E31 .510/300 cam and about 10.8 compression.

39mm choke

155 main

190air

60piot

50 pump middle hole

35 degrees total adv.

Now haven't got to the dyno yet but I put in a wideband rather than just seat test and plug reading so far 14-15 idle, 13-13.5 light cruise and 11-12 WOT right to 7000. No stumble, no bog runs real nice. I also run Todd's stacks, short SK manifold and I'm at 1650 feet alt. Most of the 3.0L or bigger motors I've seen dyno sheets on with your cam specs run 39 or 41 chokes you might want to examine that.

Indeed, the 37 chokes could be too small. Regarding one change at at time... I have become learned. Separate threads occurred... here is the one that I am most current with.

Since I already own a TWM and Electromotive fuel injection setup, spending money on new (or machining of some 34's I already have) chokes is not too likely. The TWM throttle bodies are 45's... with no chokes.

May 10, 2015

Decided I would try 195 Mains to see what the change in AFR would look like. Obviously, I'd like to lower that hump in the AFR in the 5400-6400 territory if at all possible. So, I figured I see what the 195s would do.

It was a pretty substantial change. And, as expected, AFR got richer where I didn't need it to also. I haven't had any luck getting airs to lean out the top in, so I am hesitant to order something bigger than 270's - I don't think it will make a difference.

So, now the question is, which of those two plots is better? Should I stick with the 195's, or go back to the 190's.

May 7, 2015

I'll refer you to Dan Baldwin on this one:

Every biggish-cammed highish-hp carbed L6 build I've seen does that, it's due to reduced V.E. and multiple carburetion in that rpm range. I.e., air comes through venturi once, gets fuel, then some air gets pushed back through the venturi due to late intake valve closing and picks up more fuel, then gets drawn through again, picking up still more fuel, at the next cycle. With fuel injection you could improve the A/F ratio, but you'd still have a big torque dip there, as it simply doesn't breathe well at that rpm. What works great at 6500+rpm doesn't necessarily work all that great at 3800rpm...

Interesting... I was starting to suspect "reversion" and came across another hybridz post (sometime during the hours and hours of searching/reading) where another member addressed their "bog" issues completely by adjusting the cam timing. My engine builder spec'd out the cam timing with three different settings on my adjustable cam sprocket. One of my recent tuning changes was to retard the cam a touch to see if it improved the wide open throttle (WOT) below 4k situation. Retarding the cam changes intake valve opening and closing times relative to piston position, so it has an impact of the amount of reversion.

Ah... so when you pulled off the rocker cover, the number one valve (exhaust) was as pictured: valve keepers missing and valve bent (it looks bent to me...).

You mention a rock or a nail... Were you running without an air filter? How about a pic of the number one spark plug?

May 5, 2015

It looks like those cnc rockers (that one anyway) has had holes drilled through it... perhaps to decrease weight. I don't see those holes in the earlier pics of them you put in the thread. Am I seeing that right? Did they come that way?

Did you pull the valve retainers for that one valve, or were they jettisoned during the failure and that is how you found it? I'm coming up with theories...

As an aside, I noticed you said that the engine doesn't deal at all with WOT below 4k RPM. I've been working on tuning in recent weeks and have been chasing after that same issue (if I recall correctly, we have the same cam). Been using a LM2 data logger and making changes one step at a time. A vexing problem has been its inability to deal with WOT in higher gears (3rd, 4th, 5th) and lower RPM's (less than 4k in 3rd - I don't even attempt such a thing in 4th or 5th anymore). I have found a combo that allows full throttle in first without issues and once the revs are up, I'm all good.

(Edit: Nice - I just saw your AFR curve... that is the same mountainous beast I am dealing with! )

Still, the Mikuni's (44's) are losing their aura. FI is going to happen sooner rather than later.

May 3, 2015

I've been trying to lean out the top end as of late. But, I have found that even substantial size increases has little to no effect in AFR at the high RPM range. For example, here is an AFR vs. RPM plot of the following jet combinations - the dotted line is the run with a 250 air jet:

Main 190

Air 250

Pilot 57.5

Pump 50

Choke 37

vs.

Air 270

I bought the 270's this past week and tested them this weekend. It seems no matter how high I go, I can't change the AFR at the high end.

Here is another plot. This one shows a comparison of a much earlier run when I had 180 Mains and 220 Airs (dotted line), and everything else is the same vs. the latest 190 Mains 270 Airs that are in the car now.

This is the problem... I can't get the upper range to lean out. What could be the problem? Are the carbs somehow not getting enough air?

May 1, 2015

Thanks Brady. That's my guess too.

Again, great feedback with the tensioner Garrett, thank you. That's crazy! Did enough of a collision occur to lower / lose compression, or did you luck out? I can't quite make out your image. I didn't touch the tensioner, only the engine builder did. Slippage is possible I suppose. The chain was tight to the touch when I took the pic of the idler gear and since then the bolts haven't moved visually. I would think it would have to slip noticeably in order to jump a tooth, and would also think that all cylinders would be affected equally?

Thanks for the oil pan suggestions, Jon. The Nissan Competition pan seems to be made of unobtanium, it didn't turn up on any of my internet searches, though it steered me to Kameari (again). Evidently the Kameari pan is > $1,500!? Haha! I might be one of the fools who's willing to sacrifice price if I feel I'll get what I pay for, but that's a ridiculous amount for a similar product. Looks like I'll be steering toward AZC. (Now that I think about it, I didn't think to check if Nissan still offers it. Too obvious?)

I had a chance to dig out the copy of my dyno runs from a couple weeks ago. Evidently my memory with the numbers were a little generous! Haha, the poor sap was trying to make up for his heartbreak... The tale of the tape: 235 whp, 205 ft-lbs. Not shabby at all, however comma, the 2008 dyno was 264 whp, 249 ft-llbs with street headers and a lesser, non-oxygenated VP race gas. (Not that I think I had any oxygenation after 3 years, I simply mean that non-oxygenated fuel produced 264 in VA.) I went ahead and attached the 2008 dyno runs for comparison.

As JohnC pointed out regarding my A/F ratio, it's awful. [below 3,500 RPM especially, which he called out predictably I might add!]

As for the performance: fuel, friction, tune...? I'm not worried about the performance discrepancy at all, it drives like a totally different engine in the most intoxicating way. The purpose of the dyno pulls were to confirm all was well mechanically and timing-wise with the engine so I could confidently tune the carbs, order more jets, burn the fuel drum up and put more miles on the engine before ordering new tires, doing a full tune with fresh gas and competing. I was running the same race gas from 2011 ("fresh" from drum) and didn't have sufficient time to dial in either A/F or timing on the dyno, but certainly improved performance significantly. Sure, the ratio was ugly, but it drove like like a son-of-a-bitch to and from the taco stand. (Cue Al Bundy pose, living the glory days...)

Carburetors: For me, the dyno is to dial in my timing curve so that I can productively be free to tune my carbs week-to-week before races. With timing locked in, I can road-tune the car to respond to the pedal better far than dyno pulls can. WOT doesn't help me for autocross, and leaves me with a car that doesn't drive in mid and low-pedal positions under 4k, not even with a feathered pedal. Butt-and-ears dyno? You bet.

Yes, fuel injection is coming... but not for another year or two. I still want to progress via a *tuned* comparison from carbs, and I still plan on larger DCOEs as an interim comparison as well, simply because I want to enjoy competing with carburetors for a couple of seasons before spoiling myself as a driver and going to FI. WOT has never been possible until around 4k with this cam, so there is definitely some area under the curve to be had the day fuel injection arrives.

Hanging onto carburetors is a product of my amateur perspective and my desires. If there are opinions out there that carburetors are *foolish,* I'm formally asking for them! There are reasons that I'm in the same boat again with this engine, but I don't know what the reasons are. I find it plausible that an "ok" carb tune under load might be fine, but the break-in moments when the engine has never turned over before and isn't under load... perhaps those moments are more crucial than I realize? (JohnC, were you holding back?)

Perhaps: [amateur with carburetors] + [engine with tight tolerances] = [margin for damage/failure]?

I don't think so, but I don't know. I keep referring to the first build in my memory and on YouTube. I was "more" of an amateur in 2011, and that engine purred from birth. The data points conflict, so a proper conclusion cannot be drawn. Productive criticism and debate aside, I'm particularly pleased with shapes of what the curves are trying to be. Despite the poor tune, I remain encouraged that VE has improved.

Regardless, it's on! I'm in a new town all as a single guy staying in a hotel, but I found a storage unit for my Z that gave me permission to pull the engine out, keep a drum of fuel, etc.

[side note -- in this case it was very challenging being an honest, responsible citizen in a free economy. I was judged and rejected by several owners because they have had "rif-raff" type tenants abuse their storage units in the past. I finally found a guy that appreciated my honesty so much he said yes. And a handshake. The way men used to shake hands. ]

Very fortunate I brought my cherry picker with me in the front of the trailer! Zed willing, I'll have the block out this weekend...

There is some nice art here - thanks for it.

Here is the oil pan that mortensen was speaking of. Seriously consider it. I got one not that long ago... I think 4 to 5 weeks is lead time much cheaper than the Kameari one.

The shiny "sliver moon" on the right side of my pic indicates exhaust valve to piston contact. My leak down before and after the chain being off a tooth is the same 2 to 5 % across the cylinders. I think I got lucky, but will have to check again after some more miles to know for sure.

April 26, 2015

Any updates?

April 26, 2015

Here is what I am referring to:

...the table on the piston top is juxtaposed to the table on the cyl head = squish/quench, etc = high c.r. resistant to knock.

Those look a lot like the JE pistons in my engine.

April 25, 2015

Just thought I'd put this out there. In all of my researching on the forums and elsewhere, I have never come across this value. Honsowetz says 1.5. I've seen several mentions of 1.0 in these forums (which is what the Mikuni Manual shows for 40 phh). The Mikuni Manual does indicate 1 1/8 turns out, however.

G

April 23, 2015

On my engine, I believe the Kameari tensioner will allow the chain to loosen enough to slip one tooth on the crankshaft gear sprocket. That happened to me recently (though I pulled the upper tensioner part out completely when this happened).

The car wouldn't rev right and the engine was louder. I was thinking that the valve adjustment had gone out of wack, so I tightened up the clearances a couple of thousandths. However, that made the noise worse - so I shut it down. I bought a bore scope and found that the exhaust valves were tapping the pistons. That and recently messing with the tensioner led me to suspect the cam timing was messed up - which is what the problem was.

Here is a pic of the bore scope LCD screen:

Any changes with the tensioner that might have allowed the chain to slip a tooth?

G

April 21, 2015

I've had cars that burned oil in the past. At 500 miles per quart it becomes very noticeable. How much oil was actually left?

At several quarts per 100 miles, there really will be a constant smoke screen. I think you can rule burning it out - also, go to rear of the car and check the rear panel... if it was burning it, there is going to be tiny oil droplets all over the entire panel.

A leak of some sort is far more likely... to lose that much oil in that brief a period of time. Look under the car from the engine back for evidence of any leakage. That much oil leaking is going to coat some portion of the underside of the car.

The coolant system couldn't take on that much oil either. I think the entire capacity is like a little over two gallons... Easy enough to check if there is oil in the coolant. Just drain and examine.

I have the kameari chain tensioner. When it is too tight, it does make more noise, but you really can't put any significant load on the engine by having it too tight. Cross that one off.

Very sorry that this happened. Do what you can to distract yourself from it... until the emotional part dies down. Don't dwell in it. You'll get it back to where you want it to be.

Just watched the video. Are you running an open exhaust?

April 21, 2015

Your study is interesting!

You should plot the AFR vs. Rpm. It would be easier to compare data.

I just rediscovered this suggestion from you last night while reading back through this thread - it helps to have all of this info in one place to see where I have been and to hopefully inform where to go next. I am playing with AFR vs. RPM. Will see if I can get some plots together.

April 21, 2015

Spent the time to adjust the accelerator pump lever throws to the Mikuni manual spec. - 7.5 mm. They were about 4 to 5 mm prior to doing so. I went out after that change and got new baseline curves. That is the solid line in the plot below. Interestingly, my lean spike at WOT is back now.

What I had in the carbs for the baseline:

Main 185

Air 250

Pilot 57.5

Pump 50

Choke 37

Also in the plot are the dotted lines which is the change to 190 mains after recording new baselines (no other changes):

No matter what jets I throw at this thing, I can't get that hump in the middle hammered down. Stepping up the size of the mains is making the curve richer for the entire RPM test range. While the bump in the middle shrinks, the AFR at the ends - just after WOT and full throttle above 7000, also descends.

Combo in the car is now:

Main 190

Air 250

Pilot 57.5

Pump 50

Choke 37

I am pretty far outside any other jet combo for Mikuni 44's than I have seen for any other 6 cyl. Z engine. Seems like I have something weird going on... wish I could identify it. Need to start thinking outside the box. Maybe I should revisit my cold air intake system... or maybe I have some weird fuel pressure fluctuations as RPMs change...

April 19, 2015

Since I've been having various issues trying to tune my Mikunis for a new engine, I decided to check my pump lever stroke measurement - this is something that I did not check when I put the carbs on the car.

The Mikuni manual clearly shows that the pump lever is supposed to move 7.5 mm when a cotter pin is used in the center of the three holes on the rod - for 44 PHH carbs.

With the carbs still on the car, I used my borescope and a piece of stiff wire with the 7.5 mm measurement clearly marked on it. Operating the linkage to full open, I saw the pump lever move about half the 7.5 mm distance.

Now, two of my Mikuni carbs were near new when I bought them, and one is obviously a bit older. However, all three of them have about 3-4 mm of stroke instead of the factory spec. The spec being off, especially for the new carbs is really surprising. I can't believe it... and then the older carb was set the same. I even have another rebuilt one laying around, and I checked that one too. It had about 4.5 mm of stroke.

Is there a chance that factory manual is incorrect? Anyone else ever gone through the trouble to check their pump lever stroke dimension?

I have now pulled each of the three carbs off the car and am proceeding with setting the rod such that the pump lever travel is 7.5 mm when the linkage is operated (using cotter pin in middle hole). I hope I am not making a mistake because its a pain to go through all of this for a misprint.

April 19, 2015

I managed to get a few runs in despite the rain showers. One goal for today was to check to see if tightening down the intake manifold and header nuts changed anything. I saw essentially no change due to that. Next, I discovered that the front carb was being held to the manifold by only the top two nuts. It took me forever scrounging around my boxes of Nissan hardware to find a couple of 8 X 1.0 mm nuts for the carb isolator studs - what an uncommon size! I also changed out the pumps to 50's because I have seen that anything less causes a spike on full open throttle for the tuning runs I have been doing. Here is a comparison of 45's to 50's:

The brief "jump" to lean at WOT, is essentially gone with the 50's.

This is a run in both 3rd and 4th:

It's not exactly easy to see, but the AFR curve is actually very consistent - just compare the same RPM in 3rd vs. 4th. As you can see with the stat markers I have, it doesn't matter what gear, the curve is essentially the same. I've logged a large number or 3rd and 4th gear pulls now, and I have overlayed them and compared the differences.

Right now I have this combination in the car:

Main 185

Air 250

Pilot 57.5

Pump 50

Choke 37

By looking at 3rd in this chart, all I am dealing with is revealed. Even with many main fuel and air correction jet combinations, the shape of this curve generally does not change.

I have low 14's at steady state cruise 3100 RPM in 5th. I have low 13's at steady state 4600 RPM in 3rd. I can snap open the throttle at 4600 RPM in third without a lean spike. The AFR drops very briefly to low 12's, then climbs. It crosses over to the 13's around 5200 RPM. 5800 RPM is often the peak in lean AFR around and is about 14.4. Then AFR turns downward again. I don't see below 13 until about 6500 RPM. AFR keeps marching downward linearly from there until about 7000 RPM - where it hits low 11's. It does pretty much level off right at 11... I have rarely been going much above 7200 for now.

Since low 12's for WOT through the power band of this cam is the goal, my next move will be to throw some 190 main jets in. 250 airs are as big as I own at the moment, but it looks like I'm going to need to buy something bigger.

300 airs is the largest size - I am at 250 now. Perhaps I need to start thinking about some larger outer venturis to reduce the "pull" on the aux venturi.

April 16, 2015

What happens when you do a slow-roll-on to the throttle compared with a WOT Mash?

That makes a huge difference. If I squeeze the throttle, AFR on the screen of the LM-2 doesn't go as low, and the engine doesn't misfire. I have to squeeze slower in higher gears vs. lower (4th vs. 3rd specifically - I haven't even tried full throttle in the .745 overdrive in 5th anytime recently). I have to squeeze slower at lower RPMs vs. higher. Anything over around 4500 RPM right now, even in fourth, and I can snap the throttle open and I am ok, meaning I don't get the low to mid 10s and perceived misfire - the AFR still drops into the low 11's initially though.

What happens when you disconnect the Pump Plungers and try the same thing with both Mash and Slow-Roll-On?

Haven't done that yet. I can put it on the agenda for this weekend. Bummer is I have to travel about 6 miles through stop and go to get to my "test area" on the interstate. I could schedule another dyno session.

Come to think of it, you are running an appropriate rear end ratio, right? Not the 3.36? More like 3.9 or 4.11? N/A Carbbed engines need to twist to work well.

I've got an R200 4.11 in the car.

Here is another plot from when I had the best set up in the car thus far. Because the tune was improved with the change I made for this run, I decided to snap open the throttle at lower RPM in third than I had been doing - to test that issue. I eased off until I was around 4k instead of 5k, and quickly went WOT.

April 15, 2015

Sometimes I assume too much and think people will make these interpolations. Reason I say it was because the process of writing the Toyota example reminded me of my dunderheaded old USAF Supervisor who had 2TG Toyotas and was convinced he needed to replace his entire brake system because there just wasn't sufficient braking. Long story short was "Wait, is this the car you put the TRD 304/308 Degree Cams into? The one that won't idle below 1,700?" He was convinced the car should work like stock with hella cams in it, and thought idling up to 1,700 was wrong. He had brakes driving down the road, just not at "idle"!

Same thing here, I'd say don't expect much below 1,600 at all, you don't put your car into gear and idle it down the road. This is an off-idle test, and off idle is 1,600-1,750 rpms. You just won't work well below that due to carbs needing vacuum to properly atomism the fuel. Up the engine speed and your atomization improves.

I started out thinking I could tune these carbs for "acceptable" AFR with full throttle application in 4th gear from 1200-7700 RPM... even with this big cam. Right now, I can't use full throttle at below 4000 RPM in 4th without a dive of the AFR to mid 10s along with experiencing what I perceive to be engine misfire. The taller the gear, the more prevalent this issue is. If I am in first, it isn't a problem. My understanding is that I am a still a long way from what I can yet achieve with these carbs (and my specific engine) from a tuning standpoint. But, yeah, I am starting to realize that I won't be able to achieve the original goal until I switch to the Tec GT and the TWM fuel injection.

April 14, 2015

Keep in mind Mikuni PHH were OEM fitments on probably a MILLION or more Toyota DOHC engines from 1967 into the 80's (with catalysts!!!)

If you can get Toyota drive ability and reliabilitynout of them in a 1980 Camry GT, you can do it on an L-Series.

It's not me just saying it, Toyota proved it! My 76 Celica GT would lug in fifth gear from off-idle to redline.

So would my Fairlady Z with the L20A and 40PHH's from a 2TG Toyota.

As would my blow-through 44PHH turbocharged 73 240Z....and that was no small feat.

I'd like to think I can figure it out, but I am wondering if my cam and my intake as well as cylinder head porting haven't made that too tall of task for the limited action of swapping out jets. I also could be experiencing some reversion...

I'm going to try to get the AFR curve from 3500 RPM up to be "right" and then see where I am with full throttle dumps at 1200 RPM (that is as low as I go - it is my idle speed for this cam) up.

April 12, 2015

I was able to work on the tuning some more yesterday. I started the day with:

Main 180

Air 250

Pilot 57.5

Pump 45

Choke 37

Last change was going from 240 to 250 air correction to try to produce a leaner AFR above 6700 RPM. Here is what actually happened - the dotted line is the previous run with 240 airs - the solid line is the current run with 250 airs, both are in 3rd gear:

Interesting that the bigger air jet caused the range between 5300 and 6000 to lean out more while causing the range from 6000 up to get richer. Isn't that the opposite of what you'd expect?

Because the AFRs were at or above 13 for all of the graphed RPM range except above 6600, I decided to try upping the mains another step to 185:

The dotted lines are the 180s from the previous run. Only the mains were changed - again in 3rd gear. The AFRs were made richer across the test RPM range.

Here is a comparison of two 4th gear runs. The runs differ only in that the prior run (dotted lines) had 180 mains. This run has 185 mains:

Interestingly, when I went to full throttle on the 185 mains run, AFR didn't dive into the 10's as has typically been the case. I am more conscious of the problem, however, so it may just be that I am squeezing to full throttle over a couple of seconds instead of snapping to full throttle.

Since going with the bigger 250 airs richened the top end and leaned what has been consistently the leanest RPM area on many plots, I'm thinking the next step will be to lower the airs to something like 230. My prediction is that my plot will flatten out - richer in the 5300 - 6000 range and leaner in the 6000 plus range.

But first, I'm going to tighten up the manifold nuts. I may have some slight leakage at the header, and I want to be sure that is not the case. I'll do that and make a plot run. If nothing has changed, then I will change to the 230 airs and see what happens.

April 10, 2015

Maybe over-simplifying but wouldn't drilling an extra hole in the camshaft give the same effect as the added spray bar? The holes in the stock camshaft are somewhat randomly placed. A person could pick a spot, maybe at the start of the ramp, to improve the odds of sufficient lubrication. Same increased volume, better placement of the oil.

With that in mind, it might be useful to know where the hole is on the lobes that fail, assuming an internally oiled camshaft. Maybe there's a clue there.

Well... you are onto something there. Years ago, I had a Datsun 510 that I put a 490" / 290 cam in. I think it is in the How to HotRod your Datsun book that any lifts over .490" require the addition of an external spray bar for the l series 4 cylinders... (I don't feel like taking the time to double check the specifics right now). Anyway, I had the cam in the car and it was fine. But on a trip back home (college days) I spent some extended time at 100+ miles per hour, and when I got home I had one wiped lobe (around number 5 or 6). Tom Howen (friend and co-conspirator of David Weber of Malvern Racing Fame) put it in his "varsol" tank and shot the fluid through the cam bolt hole and observed the flow. It became obvious in an instant that the location of the oiling hole for the lobe that wiped was 180 degrees from optimum placement. So, on the new cam that went in, only one mod was made - Tom set it up in his mill and drilled straight through the oil hole in the lobe that had failed. Thus, that one lobe had two oiling holes, and the cam was unmodified otherwise from the previous one.

I had no issues ever again - and I beat on that car mercilessly.

So, you could absolutely "fix" a lot or improve things substantially by better placement of the oiling holes. That said, I do recall someone saying that oil "spray" from a spray bar in addition to cam oiling helps cool valve springs which will extend their life. FWIW.

Have you primed the oil like you did in the video with and without the spray bar? I am interested to see if the "time" it takes to reach the cam is the same at the same drill speed. Also would be interesting to see if the "volume" coming out the cam holes are noticeably higher. Sucks to have oiling issues and since I am kind of in the same boat you are in more questions come to mind.

I might have missed this but are you running an oil cooler or a competition pan?

No, I haven't primed without the bar. And, I am not running a cooler, but I do have a competition pan from DP Racing.

April 10, 2015

I don't have a pic, but I do have a video showing it rather well.

April 10, 2015

Just came across this thread which discusses reversion. Kind of seems like what I am experiencing. Darn it.

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Posts posted by inline6