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NA 3.1L=>head & camshaft questions. No shortcuts, max

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Well, I've always had a crack in the iron of one of my exhaust valve housings (still pissed at that %[email protected]! guy), and it's time I rebuild another head. I have an idea of what I want to do, but I figured I consult the experts before I drop the big $$$.

 

And yes, I just spent an hour reading threads. I couldn't find anyone asking questions about setups/uses similar enough to be completely comfortable with just doing it. I did see a lot of profiles that looked like the kind of guys I want to talk to!

 

What I have: 3.1L L28 stoker with triple weber 40mms, Electromotive ignition, and headers of course. I just totally revamped my suspension and brakes.

 

Soon to be: 3.9 or 4.08 R200 with Quaiffe ATB. I will remove my KN chrome filters :cry: and replace those pretties with a ram-charge intake. I will use a scoop from the radiator area that will have a pressurizable collector for the carbs. => NA boost.

 

Use: Uh, I'm in the Navy. The car is my wife. Like all good wives, she takes my paycheck while I'm gone, and like a good husband I let her. :D It runs 110 octane whenever it is driven. (the compression, although unmeasured, is too high for 93) The car is 90% entertainment, something to look forward to when I come home. I intend to kick some ass at autocross and perhaps do a few road race events years down the road.

 

The goal: the best NA engine attainable. Damn the price, whats the best?

 

 

I've got another, perfect condition E31 head. I planned on rebuilding with that. So I offer the question: is it better to have the high compression of the E31 head? Is the reason most people recommend E88/N42/P90 simply because E31 is so impossible to find and compression is too high for the 3.1L? Given the fact that it will likely continue to drink 110 octane, do the experts agree to go for the compression or is there something I am missing?

 

The head, whichever one I do end up with, will have each head flowed identically and the combustion chambers will be matched. (the goal is 6 identical mini-engines pushin on the same crank. why not? each cylinder has its own intake system separate from the others) I'm currently trying to find the best machine shop in the area of the car (Arkansas) (I know....)

 

As for camshafts...I have wrestled with this for 2 years now. Do I want the nasty cam that has power above 4000 rpm or something more streetable? I have had a hard time. The main concern is that it will require some skill to wield a car constantly above 4k at an autocross. Enter the quaiffe atb and a lot of fun! I am currently leaning toward a less streetable cam (~ .500" lift, 290 dur) since gas mileage and practicality was never what I had in mind. What grinds do you guys recommend for this setup?

 

Any experience would be appreciated! Have any other 3.1L L28 owners regretted a decision with a cam? Anyone love theirs? What was the grind and where did you get it?

 

Thanks a lot, this was a long read!

 

:cheers:

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The E31 is great, but you need to install bigger valves and unshroud them to take advantage of it. It also has a really bad tendency to erode the coolant passages that the later heads don't seem to have, so you may want to double check yours. You may also consider milling a P90 .080 and going that route (which is what I would have done in retrospect).

 

I've got a F54 with flat tops and E31 and an American cams regrind .490/280 cam. I wish I had a little more duration. .490/280 is not that radical IMO, especially considering your very high compression that you will see when yours is done. Mine idles pretty smooth, for what it is. All the cams I have seen tend to go from .490/280 to somewhere in the .560/310 neighborhood. There doesn't seem to be a middle ground cam like this .500/290. Have you found that grind, or is that what you are looking for? I'd be interested to know who has it...

 

I would prefer lower gears for autox. I've got 3.70's and am looking to go to 4.11 for just that reason, so I think you're on the right track there.

 

You can probably save yourself some gas $$$ by cutting the race gas with premium unleaded. My setup requires about 95 octane, but I think I could get by on 92 if I had a little more duration. I seriously doubt that you are needing 110, or that you'll need it with the new motor. If you mixed the 110 with 92 50/50, that gives you what, 101 octane? That should be plenty I'd imagine. You can keep cutting it until you find out what octane is necessary, and save some cash.

 

Jon

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You're better off going with an N42 or a P90 head and using custom pistons to get the comrpession you need (at least 12 to 1). I don't know anyone using an E31 head and getting more then about 275hp.

 

Jim Thompson at Sunbelt has a lot of different cam grinds for the L6. My cam has a .534 lift but I don't know (and Jim won't tell me) the duration or the lobe centers.

 

The goal: the best NA engine attainable. Damn the price, whats the best?

 

I would argue that the 3.0L Jim built me is the "best", but I'm hardly an unbiased source. Dan Baldwin, Mike Eckhuas, and a few others have some pretty powerful NA L6 engines. You'll need to be pushing over 300hp at the crank and over 260 at the wheels to compete... :-)

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Thanks for the advice, guys.

 

I think you're right about the octane, Jon. I hadn't thought of cutting the gas, that will definately save some cash. I think 50/50 would run just fine! I may be able to cut it a bit more than that. Some experimentation is in order...

 

The grind I was thinking of was fictitious, simply higher than the cam I've got on it now. Some guy named Pierre (Pierre Z) claimed it was his grind (.476, 284 dur I think) and ripped me off for some head labor. He's the guy who cracked it.

 

John, I take it you are very happy with your cam and would recommend I give Jim a call? Which head are you using with your 3.0L?

 

Any other Jons or Johns out there with more experience to offer? :wink:

 

Thanks.

-Mark

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:cheers: You can use the E-31 head and get good results. I am running a E-31 head on a L-28 engine with bigger valves and a mild cam/triple webers (45 MM). I am using dished pistons in it for unleaded/regular gas. The head has been worked over by Heads by Paul in Denver, CO. It has the cam from Motorsport Z that is rated by them best for the webers and the street. It is made by schneider with the 270/280 duration. It runs well on the street and nice on the road track. I did have a Sig Erson cam in it for the track, when I had the L-24 block in it. It was the model 290AS with 296 duration and was good past 6000rpm. A strong pulling cam for track and not to good for street. Right now working on a new block (.40 over L-28) with a E-88 head for the track. Will have to change it before I race it type thing. Hope to have 12:1 compression with the track engine. Keep us informed on how you are coming along. Take care, Rich. :-D

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John, I take it you are very happy with your cam and would recommend I give Jim a call? Which head are you using with your 3.0L?

 

Absolutely give him a call. 770-932-0160. Talk with Jim or Chet. My car has a highly modified N42 head. Find the "Defcon 1" thread in the 6 cylinder engine board on this site.

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Ditto what JohnC said re Sunbelt. My cam from Sunbelt is something like .550"/305 or 310 duration. Those guys probably know more than anyone else about building up high-perf NA L-series engines at the moment. That said, I do have a big torque dip at 4200 rpm. I dunno if this is strictly due to the cam though. It goes way rich at that rpm, looks like multiple carburetion. Extremely difficult to get parts for my Japanese OER carbs. I'm sure John's FI motor has no such issues.

 

No regrets going somewhat big on the cam. I don't street race or fool around on the highway, and though the bottom end torque is ragged on the dyno, I just never drive the car that way (never full throttle below maybe 3500 rpm. The car is light enough and the displacement big enough that streetability is actually pretty good, since nothing over half throttle is called for.

 

If you want the BEST, and you're fiddling with high octane anyway, I'd just go ahead with the full race compression ratio (~13.5:1?) and not bother with mixing with pump fuel. Cost of fuel is high, but why even bother with it at all if you're not going to take full advantage? For my application (I drive as far as ~500 miles to get to track events), I went with a CR of 11:1 to run on 93 pump.

 

For what you SEEM to want, bigger carbs may be in order. My torque begins to drop off at ~6000, peak power is at ~6500, with 45mm carbs and 38 or 39mm chokes.

 

Actually, you really want fuel injection.

 

You should be able to get whatever CR you want with whatever head you go with. I.e., you don't need an E31 for high compression. The 2mm HKS head gasket can be modified by removing sheaves from it to tailor the CR. My engine's head gasket has two .33 thick layers and one .5 layer for a 1.17mm head gasket.

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Dan I can't help but think that your carbs should be plenty big for 8K on a 3.1. In looking at your previous dyno charts, I think your spark starts getting irratic above 6.5K. I agree that 45's would be a better choice for Mark, but I don't think you've run out of carb. Could be the limitation of the gears on the dizzy drive. Maybe yours are worn??? I know the Pertronix unit only has one sensor, maybe the ZX dizzy style where 6 triggers line up to send the pulse would be better... I don't know.

 

I know you don't believe in the importance of quench Dan, but for Mark's benefit, there is a large contingent of engine builders who will tell you that the piston needs to be close to the flat quench areas of the head to help combat detonation. If you stick a thick headgasket in there you keep the piston farther away from the quench areas basically rendering it useless. I have heard .035-.045 and I've heard .035-.060. This is why the P90 or the E31 would theoretically have an edge over a N42. On the other hand, if JohnC is getting 305 hp out of an N42, Sunbelt must be doing something right...

 

Jon

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Wow this is awesome! I'm definately going to give Sunbelt a call here very soon.

 

I have been unable to find the Defcon 1 thread aforementioned. Is it too old to show up in a search?

 

Fuel injectors? No offense Dan, but NO WAY! Sure the numbers and ease of design might be better, but the throttle response, FUN, sound, and purity of the car would be compromised. I would never get rid of that beautiful sound!

 

As for the 44/45 vs 40 DCOEs discussion, is there a business that really knows what they are doing and can give me jet and choke sizes that work best for this setup? Everywhere I've looked I was told "sorry man, no one knows how to touch those things, its a lost art. Hell, I wouldn't even know where to get the jets" Or is it strictly the ole "each engine is its own beast" and you just have to experiment to find what works best? I'd like to see how good I can get the 40s to run before I jump up to bigger carbs.

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Jon,

I don't think I'm undercarbed, I'm only saying that Mark, for his purposes, *would* be with 40s. The dyno chart you're referring to was done with stock 240Z points, as the 280Z (280ZX?) distributor module failed on me the day before I went to the dyno! I blame Bobby. The Pertronix runs are clean up to the rev-limiter (currently 7200, old run limited to 7000 here: http://www.classiczcars.com/photopost/showphoto.php?photo=2274&size=big&password=&sort=7&thecat=500 ) Not an issue for Mark if he's going crank-triggered, just clarifying my results.

 

I never said I don't believe in the importance of "quench". What I don't believe is that the E31, P79, P90 chambers are much much better than the N42/N47 chambers just because they *look* like they should have "better quench". I'm running 11:1 on 93 pump, at 34 degrees max advance. It made the same power on the dyno at 38 degrees, I'm conservatively running it at the least advance I can without losing power.

My conclusion:

I don't *think* I'm giving away much if any CR by using the *supposedly* detonation-prone N42.

 

FWIW, my KA pistons were shaved flat and valve reliefs were machined in them, 2.7cc worth (maybe .050-.080" deep?). This was done at Abacus for the rebuild done last Winter/Spring. Pistons are .003 - .004" below deck. The head was shaved .010" by Sunbelt, and they said it had been shaved before. No idea how much, but it is still definitely an "open chamber" head. Head cc is 40.6. Some of the volume reduction compared to stock is due to Sunbelt running the valves a little proud in the chamber. Head gasket is .046".

 

I would never say the N42 is superior, I have no basis. I just don't think anyone else has any basis for saying the P-heads are superior. When/if evidence is presented, we'll ALL know more. Until then, I think my, John's and Norm's results at the very least show that the N42 shouldn't be ruled out for serious performance applications.

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You'll DEFINITELY need to experiment, but I bet that Sunbelt has a tuning area in the shop where they could dial it in for you if you don't want to do it yourself. It is an art, but if you know what you're doing it is far from impossible.

 

Mikuni parts are getting hard to come by but Mikunis are IMO easier to tune, so if you are thinking of switching your carbs for something bigger you might want to take that into consideration. Webers are harder to tune and keep in tune, but most people think that you can get more hp with properly tuned Webers.

 

Jon

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Dan--fair enough. I think you can run such high compression on 93 because your cam selection is correct for your combo. I certainly can't argue with what you've accomplished, and since I've never dynoed my Z I can't really offer up a counter argument, although I have a suspicion that I might be pretty close to JohnC's "max" on an E31 headed L series, and my engine is not really all that special. I'm just trying to give Mark another viewpoint on the heads... not trying to take away from your accomplishments.

 

Jon

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Fuel injectors? No offense Dan, but NO WAY! Sure the numbers and ease of design might be better, but the throttle response, FUN, sound, and purity of the car would be compromised. I would never get rid of that beautiful sound!

 

Well, since all L28s were fuel injected from the factory you're not compromising the "purity" of the engine by going with FI. Throttle response has much more to do with reciprocating mass then the fuel system - carbs do not have any advantage over FI. If you build a 300hp NA L6 I think the FUN will be there regardless of the fuel system. Sound is a subjective thing and I agree that a triplet of Webers at full song is beautiful.

 

But, one thing you need to keep in mind. At the horsepower levels you're discussing, going lean for a even a short time will cost you pistons. Make sure you can tune those carbs correctly and check them often if the weather changes drastically.

 

I have been unable to find the Defcon 1 thread aforementioned. Is it too old to show up in a search?

 

The search is probably out again. The post was from February 2002.

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Mark,

Regarding fuel injection, you *could* open up your wallet and go with 3x2 50mm throttle bodies and have all of the sound and fury of triple carbs. But since you already have the 40s, as you say, that's surely a good place to start. I'd try 36mm venturis. You'll have to experiment with your own particular setup. For 40mm carbs, a W.A.G. would be ~145 mains, ~160 air jets. Emulsion tubes, I dunno...

 

My carb setup is very crude, nowhere near optimized, though it probably is giving pretty close to as much peak hp as I can expect. The big dip is killing the midrange, though. And it won't pull clean on the dyno below ~3000. I've got work to do...

 

Jon,

I did run the stock cam for years, with something over 10.2:1 CR (depending on how much the head had been shaved), sometimes inadvertently running over 40 degrees of advance! The only times I got pinging was when I tried to continue running 18 degrees static advance after the initial 3.1 build (which had me at ~43 total, STUPID!), and when one of my advance springs disappeared I got run-on pretty bad.

 

I have no preconceived notions that any head is better than any other, at a given level of CR and with the same size valves. Nor do I know how high you can go with the CR for the different heads. The data just isn't out there for comparison (at least I haven't found it). All I have are a very few data points, from which only limited conclusions can be drawn. One of which is: "The N42 and the N47 are probably at least OK cylinder heads". Another one is: "Most likely, so are the P90 and P79".

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hey guys,

I just recently set one of my Z's (260 early) up with a stock f54 turbo manifold and Solex/Mikuni 44mm carbs. I've fabbed an aluminized carbon fibre' airbox with blow-off valve on the nose of the box,and for now plan on running below 10 lbs. boost until I see how it responds.

Any guesses on what I can expect from all of your previous configurations?

I've already got a 73' green 240 with F.I. and a Wolf 3-D,custom intake,To4/E etc.,etc. I'm just doing the 2.6 blow through to touch on both worlds. I love the howl of big carbs and power onset of turbos.It's a shame some of that tone is going to get knocked out by the turbine .

Any thoughts ( ON3GO has seen my green Z engine ,what did you think ON3GO ? :P

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Oh Geez, so sorry JohnC,

My bad....I thought the hybrid mix might be a blast to try since so many of us have already made so many different multi-carb 2.8-3.1 efforts ! I'll be more disiplined in trying to join in on the next thread ,again everyone, I apologize for the confusion John seems to think I've brought.

Vince :roll:

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Following this thread with interest. You'd think somewhere in the world is a book of dyno plots for various lift/duration cams that we could see (Note to self: Justify this project as a MSME thesis). I guess if there were, the cat would be out of the bag and it would be all over for the engine builders!

 

All I want is a cam that pulls _hard_ from 2.5K to 8K, is that too much to ask? I'll buy it when I find it. My motor build progress is stalled on cam selection. Know where to find one like that?

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I gave Jim at Sunbelt a call and he's looking into whether or not I would need valve reliefs in my pistons to clear the valve lift. I bought the big bore kit directly from Nissan Competition in 1998. (R.I.P.) Does anybody know if those pistons can clear .525-.550" valve lift? The catalog I bought the parts from say that the pistons have a positive deck height of .025", but I have no idea how to use that information.

 

Chances are it will have to be measured since there is no way of knowing the history of shavings, especially since I will likely use a 1mm gasket. Chances are that I will just have to get a set of custom forged pistons. And I thought at least my block was done right. How dissappointing.

 

On the bright side, it will give me a chance to swap in some prettier pulleys for the re-balance, getter some better paint on the block, and gut the engine bay to clean up the wires and give it a fresh coat of paint.

 

Might as well do my planned tranny and ATB 4.11 diff swap then, too.

 

As for John Bs idea of dyno plots, why not start a stickie where each graph submitted also has the member's comments with the cars setup. One for NA, one for Turbos? I'm sure this isn't a new idea. Administrators?

 

Damn, this is gonna cost some serious cash...I may have to wait a bit to get it done. Okay what really happens is a loan gets taken and paid off later while I'm out to sea. Let's be honest here....

 

...I can't wait...

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I'll be more disiplined in trying to join in on the next thread ,again everyone, I apologize for the confusion John seems to think I've brought.

 

Ease up. Check the site guildelines in the Announcements forum. Although thread hijacking occurs here its not really something we encourage.

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JohnB, if you've got a 4.44 rear gear, why are you trying to find a cam that works at 2500 rpm? Seems like you could get a cam that doesn't start til 3500 or 4k and still keep it in the revs with that diff.

 

Or were you asking rhetorically? If you find that cam, BTW, let me know...

 

Jon

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Slow second gear corners mainly. I'd like to stay out of first. Seem to be getting a lot of those lately. The 4.44 gears make that possible, but I run out of second gear quick now too so some times up to third for just second or two, then back to second, brake and start turning in all at the same time. I'm not coordinated enough to do all that turning and braking and shifting at the same time. So if I could just stay in second (like an S2000) on the tight courses, maybe they won't beat me anymore.

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(R.I.P.) Does anybody know if those pistons can clear .525-.550" valve lift? The catalog I bought the parts from say that the pistons have a positive deck height of .025", but I have no idea how to use that information.

 

Valve reliefs are required for .550" lift! When I first installed the Sunbelt cammed head, I ran the cam a little retarded to get decent intake valve clearance (.040"), which I checked with a lump of clay. Unfortunately I didn't check the exhaust side. A year later when the motor had to get rebuilt, we found deep dings (~.080") on each piston from the exhaust valves! That was with a 2mm gasket. Abacus Racing did the rebuild, and did the valve reliefs in the new pistons. Chuck at Abacus is GREAT, very conscientious, and experienced in building serious (GT2) L-series race motors. He checked all the clearances and mocked up the assembly a few times to get close to the CR I wanted. VERY tight, even with the reliefs.

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