Give your opinion

[agemeansnothing]

I have had many different people tell me two different things so, I was wondering which head has better compresion? Not just compression but over all, the E31 or the N42? Personally I have a N42 and I'm looking for a E31. E31s or way rarer than the N42s so that doesnt help me. I dont know how the E31 operates because my brother and I havent put his in his block yet. I think the n42 overall is a very good head ( especially with a stage 2 camshaft). If you have had either or experience give me your opinion on what you think of a better head.:bandit:

[Ron Carter]

I would suggest that you do some research on this site. This has been discussed several times in the past.

That being said, I would suggest that you look at an N42 or a P90

[Arne]

Depends on what you have in mind for the rest of the engine, and also your driving style. Yes, the E31 will have a bit more compression, but the valves are smaller. If the engine is mostly stock, and used for normal street driving (most often under 5000 RPM), there may be a SLIGHT benefit to the E31. But for higher RPM - especially with a cam - I would think the larger valves would more than make up for the slight difference in compression.

I also have the feeling that the E31 has a 'magical' reputation that may not be totally deserved. People assume that since it gives the most compression, was the original pre-smog head, and is used by racers, that it must be "the best". But remember there's a lot more to power than compression, and that the racers use it in many cases because they are required to do so.

All this is just theory for me, as I have no personal experience with either at this time. But based on my knowledge of engines from decades of tinkering, that's my gut feeling.

[agemeansnothing]

What do you have on your car Arne?

[Arne]

What do you have on your car Arne?

LOL

Let's see... There's a P79 on the L28 that's in the car now, a stripped E88 on the bench, and an E31 on the L24 that's in the parts car. I was planning to have the E88 rebuilt until I bought the parts car, but now I'll probably swap the whole engine from the parts car into the yellow car instead. I'll probably put the E88 on eBay real soon - as soon as I figure out how to prepare it for shipping.

[BuDavid]

as far as I know according to my weak knowladge, N42 is the most common used to increase the pressure, but be careful with choosing the piston type, the shouldn't be flat guess.. I'm not sure, dont relay on my post..

good luck

[beandip]

Arne , arent the ITS car's required to run ''stock'' heads ? So if they are running a '70 Z the E-31 is needed ? Just a thought . I met some ITS racers at PIR and the regulations are specific on what they can remove and use on there cars. Maybe a knowledgeable ITS or SECCA racers that know this stuff will chime in. Gary

[Arne]

That's what I meant when I said that many racers are required to use the E31.

The reality is that for street driving, there probably isn't a truly noticeable difference between any of them. But it's one of those things that many people obsess over endlessly.

[240ZMan]

The reality is that for street driving, there probably isn't a truly noticeable difference between any of them. But it's one of those things that many people obsess over endlessly.

A few years ago I replaced the stock E88 on my L24 with an E31. Everything else was stock. I could not feel any difference in performance.

I think which head you use really only makes a difference when you begin to modify your engine. For stock, use what you have as long as it's in good condition.

BTW, I now have an N42 head on N42 block with flat top pistons and love it. I recently sold the E31 to a friend who is still running his L24. For me, the N42 offers more performance potential due to its bigger valves. I'm right at the limit of what I can get away with for compression ratio. The even smaller chamber of the E31 would be over the top for my setup. My point is that the "best head" question has different answers depending on the rest of your engine and any rules you may have to follow.

[agemeansnothing]

I dont think I'm really fond of the P90 head, yeah it might have the best flow but it has other down falls. Like having round ports, and inner oiler.

[Arne]

I dont think I'm really fond of the P90 head, yeah it might have the best flow but it has other down falls. Like having round ports, and inner oiler.

Wrong. The P90 has square ports, that's part of what makes it good. And I believe you can put the external oiler on any L-series head, as long as you use an externally oiled cam. Sounds to me as though it's time you do some homework before you spend any money.

[zeiss150]

The P90 is an excellent head. It has square exaust ports. Its basicaly the same head as the N42 but the P90 has closed chambers which is better for controlling detonation. On a flat top piston short block you get a CR of 8.5:1 which is not bad for a N/A engine and if you want to go turbo, its almost perfect. If you never want to go turbo, then mill the head 80thou and buy some cam tower shims along with the 80 thousands longer valves put a bitch'n cam in there, and you have a bad arse, detonation free N/A 10:1 CR motor. The P90 (and the P79) were the best of the Nissan L28 heads in some peoples opionions (don't even get started with the maxima N42 head, I'm talking about Z engines). As far as the internally oiled cam... so what... my N42 has an internally oild cam, it works great. With all of that said ...

I have a fun as hell, F54 flat top block with an N42 head with a stage 1 cam and SU carbs my engine has 9.2:1 CR because I have a 2mm head gasket without the 2mm head gasket it would be almost 10:1. The only reason I would change my set up is because I'm gonna go turbo... and if your gonna go turbo you need a better head (the P90 or P79) in order to controll detonation. My advice to you is to do a bunch of research (which you seem to be doing) think about how much rear wheel horse power you want and whether or not you would ever think about turbo. anything over 190 RWHP would require major head work and serious intake and carboration work. With turbo 225 RWHP can be reached with simple modifacations. and the potential for 300+ RWHP can be obtained for what you would spend on the Head work for a N/A 225 RWHP head.

I'm not trying to convince you of anything ... I just wish someone had layed down this info before I built my Z ... Cause I would have gone turbo for sure... now I have to do it again.

Good luck and let us know what you do.

P.S. Check out this awesome page http://www.geocities.com/zgarage2001/p90.html