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L28/E31 with webbers, or N42 0r N46????


balaguy

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I have an L28 with an E31 head, it runs great. I would like to put tripple webbers on it down the road. I was told the E31 head is not the best combo. I was told however that an N42 head would be a better combo? I s this true?? I also currenlty have two N46 heads would those be something I should hang onto???

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If you have two N46 heads, hang on to them, they'd have to be rare!:) But seriously, you must mean N47 heads which are pretty much a dime a dozen, so to speak. Also, they have liners in the exhaust ports for EFI and though I've had no problems with them in my EFI cars, I've read statements to the effect that they are prone to exhaust seat cracks. Here's a pretty good read on L series heads:

http://www.zhome.com/ZCMnL/tech/head.htm

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The 2 best heads to use are teh N42 and P90 heads because of their air flow. The N42 will do you goos if your running triples, and the P90 as well. The P90 head was designed for turbo applications to decrease or get rid of (depending on where you read)detonation with turbo applications. I would also go with an overbore kit with flat top pistions to up your compression a little bit to get better HP with your triples.

Justin

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I'd have to disagree on the P90. Because it's designed for a turbo, it's a somewhat low compression head. If you go with an overbore and flat top pistions, one will diminish the compression gain of the other. You'd end up needing to do some head work to gain enough compression to run triples. If you're going to do that anyway, why not spend the money on 280z valves and seats and put them in your E31 along with the head work that the P90 would need anyway. At least, that way, you wouldn't be buying another head. Based on the choices you listed, the N42 would be the best choice. Lose the N47s since your're talking about carbs. The E31 will work (with mods) and the N42 will bolt on and work without having to bore the block and change the pistons.

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I agree with Stephen that the N42 will be an excellent choice with webers. I ran that way for a while and was quite happy. BUT ...

if you were to plan on doing some machine work ANYWAY, then I'd choose the P90 due to its better quench characteristics. I'm running an N42 on a L28 with flat top pistons and cannot run a full 35 degrees of advance without detonation. (I originally thought I was, but it turned out my damper shifted shortly after I reassembled the engine and I wasn't getting as much advance as I thought).

From what I've read on hybridz, if you have to choose between CR and advance, you're better off reducing your CR to allow full advance than the reverse. If you are going to do work on the head anyway, then a P90 could allow you to have both a high CR and full advance.

One last thought/question: has anyone done any dyno testing to determine how much extra HP is lost on an N42 with 10:1 CR when the timing is backed off due to detonation? I wonder if it's significant, or more just a bench racing issue.

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Sblake, wasn't the P90 ran with dished pistions for the lower compression to allow for higher compression with the turbos? And also, the reason I was suggesting big bore kit is because of the triples. With the right exhast system, it will allow the engine to breath better, allowing better airflow into the engine, allowing a higher compression. Or do I have this wrong?

Justin

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The turbo engine used dished pistons and the P90 to lower the compression because a turbo doesn't work well with higher compression. The turbo increases cylinder pressure which has the same effect as raising the compression ratio. The higher the compression the more chance of detonation which will lead to engine failure. Airflow and exhaust have no bearing on compression ratio. Stock vs. stock a P90 will lower the compression ratio almost a full point vs. the N42. Something like 8.3 vs. 7.4. Even with an overbore of .120", the c.r. will only be about 7.8 with a P90 on an L28 block with no other changes. You'd want a higher compression ratio than that to run your triples.

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Something else to keep in mind with regard to CR, as you go to bigger cams with more overlap, the effect CR drops. All else being equal, which it never is :), you could run with a slightly higher CR with a larger aftermarket cam vs. the stock cam.

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There is this guy in San Diego who swears by Maxima N47 heads, he said it was because of a peanut shaped chamber. I told him I never heard that before and that the Maxima N47 never comes up on the message boards I read. He said he get huge hp gains with it. He claims that the Z N47 head and the Maxima N47 head are different. I don't know either way....thought it was interesting. What do you guys think? I have no plans to got out the local "Pick UR Part" scooping them up anytime soon.

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hey guys sorry for invading ur thread but i was wondering if some1 could PM me all the Blocks and Heads codes and what engine there off for egg

L24 Block code Head Code the head code is the E31 in this case, i was wondering if some1 could list all the engines in the l series like this, it would help me out more then u could imagen, im jus confused with how people talk bout all the diffrent head block combos n i dnt know wat is from wat, thank u for ur time

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ENGINE CASTING CODE

L24 (1970 240Z) # E31 (flattop pistons)

L24 ('71-73 240Z) # P30 (flattop pistons)

L26 ('74 260Z) # P30 (flattop pistons)

L28 ('75-80 280Z) # N42 (dished pistons)

L28 ('81-83 280ZX) # F54 (flattop/dished pistons, siamesed cylinders)

1970 through 1976 heads have square exhaust ports (E31, E88, N42)

1977-'83 heads use rounder, diamond shaped exhaust ports (N47, P79)

1981-'83 turbo heads have square exhaust ports (P90,P90a)

If you put those two lists together with information in the link in post #2 http://www.zhome.com/ZCMnL/tech/head.htm you can match up the years of each head with the blocks and get a little more info on each head. Bear in mind that this is for U.S. models. I know the model lineup differed a bit in Australia.

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