Best Head

[260z]

Which is the best head to start to tune?

How good is e88? How about e88 with FI? Do they work together?

[Royce]

Well the fact that you are in Finland certainly makes what I know almost useless. Also, much of the information I have has been gathered from word of mouth. But here goes...

Each head has its good and bad but they could all be made relatively equal with a little machine work.

In the US...

240Z E31, E88

260Z E88

280Z '75- '76 N42, '77 - '78 N47

280ZX '79 N47, '80 - '83 P79, ??-'82 P90(Turbo), P90A('83 Turbo)

E88 urban legend???- Supposedly there were two E88 heads available for 240Z. If I remember the story correctly the early cast E88 heads had the same combustion chamber as the E31 and was distinguished by a sloppy casting number and the later E88 head had a lower compression combustion chamber design and the casting number was more uniform looking. I have not verified this or seen it in any books but have heard this "rumor" in many different Z circles.

For a 240 or 260Z the E88 is often not held in high regard. This is because the all of 240Z - 280ZX heads will bolt on to any L6 and can be used with the Hitachi SU, round top carb intake. Also, most L6 heads share the same square exhaust ports so that manifolds or headers are compatible. But I don't think you should count out the E88 yet.

The E31 has about .5 higher compression ratio and a better combustion chamber design. This doesn't mean a lot on the street but in race classes that limits head work this is the only advantage you can have. The N42 has the same chamber design as the E88, same compression ratio as E88 but larger valves, sorry don't have specifics. Also, I believe the N42 has hardened valve seats and guides, but cannot remember this for sure either. The N47 is the same but has round exhaust ports.

The P79 has a significantly larger combustion chamber, to low of a compression ratio for even a turbo when mounted on a 240Z - 280Z block, but has a better combustion chamber design. I believe the valves on the intake, exhaust or both are a little larger than previous heads. Like the N47, the P79 has round exhaust ports. The P90 has the same chamber size and design as the P79 but has square exhaust ports. The P90A is the same as the P90 with the exception being that it has hydraulic valve lifters instead of mechanical. Many have shaved the P90 to make it work on the first generation Z blocks. But this requires shimming the cam towers, which others would rather avoid. And if you can find a P90A all the better because your valve train will be quieter, however, replacement lifters may be a challenge to find.

Other L6 applications - there are also other heads for other markets and other Datsun/Nissan cars. For example I have heard of E88 with FI mount points. And P79 heads with square exhaust ports from a Maxima.

Okay, so the bottom line is that if you shave a little off the E88 and install larger valves it may be just as good as any of the other heads. It really just depends on how you are going to use the car and if you are going to be under any rules restrictions. I am sure they could all benefit from some polishing and porting as well.

I am sorry if this information does not apply to your part of the world. I would be very interested to hear what was available in other markets!

I have several E88's, P79s, and a P90 and hope to do some comparisions one of these days. I have a friend that may be rebuilding a E31 and N42 so would be interesting to post some findings.

Corrections, comments, and questions are welcomed!!!

Have fun! :classic:

[Dan Baldwin]

Lotsa misinformation regarding Z cylinder heads. Basically, of the 240Z heads, the 1970-71 E31, '71 E88, and '72 E88 are all good, I've known VERY successful SCCA racers to use these. The '73 E88 head (in the US, anyway), has larger combustion chambers, and much lower compression ratio, and is NOT used in serious performance applications. Ditto for the 1974 260Z E88, which has larger exhaust valves.

Note that none of the E88s is FI compatible (not notched for injectors). The first injected head, the 1975-1977 N42, has similar combustion chamber size as the 1972 E88 head, and offers decent compression ratio. It also has larger intake and exhaust valves. It's the last non-turbo head with the desirable (supposedly) square exhaust ports. The '78-'79 N47 head is similar to the N42, but with round exhaust ports with (supposedly) restrictive liners.

Then comes the 1980+ P79 head, which has the round exhaust ports with liners, and very large combustion chambers. Very low CR, even with flat-top pistons, unless shaved tremendously. The P90 and P90A turbo heads have the same largish combustion chambers, but have the square unrestricted exhaust ports. The P90A is hydraulic, requiring no valve adjustments, but maybe not as suitable for very high performance applications.

Whew! All that said, if you don't have the Lengine calculator (lets you figure what your compression ratio will be with different heads, etc.), let me know and I'll send it to you. If you have 93 octane premium fuel available, I would aim for ~10:1 compression ratio. Unfortunately you can't get there with an L24 without shaving. However, a flat-top piston L28 with an N42 head would have you at 9.8:1, and you'd have more displacement to boot....

Dan

[kmack]

Would you see any benefit to using a N42 head on an L24 block? If the N42 head has the same chamber characteristics as an E88, but with larger valves, wouldn't it let the engine breath better? Therefore giving slightly better performance?

I've heard of people using the E31 w/ 280 valves, why not just bolt up a N42 instead?

[2ManyZs]

N42 on an L-24 works fine. In fact, someone before me put one on the 71 I have. Don't know what happened to the original E-31 but luckily I can change it back if I decide to.

The one drawback (supposedly) of the N-42 is the bronze valve seats that tend to drop as they age. Of course, a new set of seats is a lot cheaper than doing the earlier heads with larger valves if you don't have a good one sitting on a shelf somewhere..

[Royce]

Yes, I think the N42 is a good replacement choice if for no other reason then because you can find one more easily and probably less expensive than an E31. The larger valves is a nice bonus, but I wouldn't change heads just for the larger vavles unless you had another good reason to change.

Any of the E31, E88, or N42 heads look even better on a L28 with flat top pistons!

[mrh12000]

what about square port heads with weber manifold, can I hog out the runners on a round port manifold to suit?

What recommendations for flat top pistons for 280z?

Thanks muchly

[Royce]

All L6 Z/ZX heads have round intake ports. The N47 & P79 have round exhaust ports as well. It has been said that the square ports are more productive to flow but I have never seen any dyno results to say how much of a difference, if any, it makes.

I have seen "the quest for the best Z/ZX cylinder head" conversation come up many times on many different forums. I have some questions that I have not seen discussed...

What are the different int/exh valve sizes for the various US marked Z/ZX L6 heads (E31, 240Z E88, N42, P90)?

I have heard often talk about putting 280Z or ZX valves in E31 or E88 heads. Does it require machining the head to use these larger valves? (What I mean is sometimes you can increase the valve sizes by just grinding the valve seat and not actually machining the head and putting in larger seats.)

What about larger than 280Z/ZX valves in any L6 head. Has anyone done this?

I would expect that all the above has been done but it may be helpful in determining how cost effective it is to modify different stock Z L6 heads. As a Z car person on a budget the best head to me is the one that gives the best bang for the buck. I have often thought if you have a head in good shape that is the best place to start. From there you can modify it to meet your performance goals. I have heard that the E31 and P90's have the "best" combustion chamber design. Sure you could put larger valves in a E31 but I would have a hard time justifying the work it would take to get a P90 head to work well on a non-Turbo Z motor. Of course to take advantage of head work mods (big cams and large valves) you also need higher than stock compression or you could actually see less power output.

What do you folks think?

[Zsled]

So, With all this said...

If I have an L24 SU's and a L28 FI 75' both available to me what would be the best engine to do for a power increase.

I want a daily drive / AutoX engine.....

Would I use the L28 with my su's or tripple webs in my 240Z?

[Dan Baldwin]

L28, definitely. Displacement is your best friend (compression ratio is your 2nd best friend, and rpm is your 3rd best friend). You can FI, SU, or 3x2 it. Stock SUs won't breathe enough for 6500rpm+ performance, I dunno about FI. 3X2s would be better for all-out performance, if you've already ported and cammed. I ran stock SUs on my 3.1 for years, and it was GREAT. Very torquey, and I wasn't doing much track driving at the time, so the lack of highrpm breathing wasn't an issue. Likely the best autoX solution.

Royce,

Some years ago DL Potter stated that installing larger intake valves in a E88 or E31 head required machining the head an installing new seats. To get the P90 to give decent compression ratio, you have to shave/shim at least .080". My pick as the best head with the least work required for an NA application is the N42.

Valve sizes:

E31 - '73 E88 42mmI, 33mmE

'74 E88 42mmI, 35mmE

'75+ 44mmI, 35mmE

[Mudge]

Originally posted by kmack

Would you see any benefit to using a N42 head on an L24 block? If the N42 head has the same chamber characteristics as an E88, but with larger valves, wouldn't it let the engine breath better? Therefore giving slightly better performance?

I have an N42 on my 2.4L with an N33 intake, it has 3.2L worth of fuel running into it though but still pulls a 15.8 quarter (not me driving it).

[Royce]

Zsled,

Depends on whether you want to win or just have fun at autocross. It is hard to beat cubic inches when it comes to making more power! I don't autocross (yet) but I would (and did) go the L28 route. But make sure and keep you L24 if it is the original motor for you car.

Turbo's and tripple carbs would likely put you in a modified class that would require many $$$ of suspension and other modifications and developement to make the car competitive. Besides, as Dan said tripple carbs are not necessarily needed to get more performance. You can go a long way with SUs.

From what I have heard Rebello Racing builds a 200HP L24 SCCA ITS spec motor using relatively stock bottom end and carbs and mild head work. For the same money they can build you a 250-275HP L28 using modified SU carbs, L28 block, and modified head (using 280ZX intake and exhaust valves). I do not work for Rebello or have any affiliation, they are just well know local Z motor builder that I had build my motor many years ago.

Dan,

I think that makes a good case for the N42! Any L6 head could use a cam and a little polish and port. With the N42 you do that and add the 280ZX intake valves and there you go! Thanks for the info!

Mudge,

Well that is almost a second off the R/T test times when the cars were new, ~16.6 if I remember correctly. Although, with modern tires you might be able to make that difference. It is hard to compare without knowing you entire setup. Engine spec, exhaust, intake, trans, diff, tires.

Have fun!