Best head for an L28?

[fugetaboti]

I am trying to figure out what the best head would be for an L28? I'm wanting to install forged flat top pistons, bigger cam, headers, and my tripple Dellorto 40's. I currently am running an N42 head stock, but something about square ports just doesn't seem efficient. Maybe I'm wrong, but I've heard the E31 and the P90 being the best. E31 having small valves, but that could be changed I would assume. Anyways hopefully someone could push me in the right direction.

[xray]

Hey there,

If you are planning a high-comp engine, an E31 is good. It does have smaller intake valves, which may compromise some airflow. Be very careful of what you do--it doesn't take much to take the CR over 11:1 with L28 and E31. Nice big bang if using street gas...

An alternative (what I am exploring) is using the E88 head. Guy real familiar with Z's in the Atlanta area has had great success putting larger 44mm intake valves in to the E88. CR issues not that big of an issue if you are using street gas as the volume is slightly larger than the E31.

P90 is a good flowing head, used for turbo applications. I think it would work fine with NA apps as well. Later models (P90a) had hydraulic lifters which some say have difficulty maintaining. Check other Z sites for additional opinions, as these heads are primarily used in turbo-modded cars.

Honsowetz's book, "How to modify your Nissan/Datsun OHC Engine" is a good resource for your library as well.

Good luck

Steve

[beandip]

According to what I have been told the P-90 and P-79 were the latest evolution and had the best combustion chambers . The P-90 as it has been said is from a turbo motor and the 79 na. The 90 has square ports where the 79 are diamond shaped with linners. According to data the P-90 flows slightly better than the P79 , and is suposedly the best flowing head Followed by the 79. They both have the same large valves . When the liners were removed there was vary little difference and the effort required was not worth the gain. Personally I know that the P-79 when milled .030 will yeald 9 to 1 with stock flat toped pistons in a F-54 ZX block . I recomend that you contact a member that builds Z engines for compition use . Find him in the members section phred . He is a welth of information . Gary

[speedyblue]

On a side note, why forged pistons? I'm guessing that you aren't running a turbo or supercharger at high boost with the tripple carbs, so perhaps if you were intending to run a big hit of NOS they would be required. Hypereutic pistons would be cheaper and still do the job, leaving a few more $$$ for extra porting of the head or something. Even the stock flat tops pistons can handle a fair bit of power.

[texasz]

You should also read up on Bryan Little's site, Z Garage for some additional information on heads and an L28 build up.

[zguitar71]

Part of the reason for the P-90 and E-31 popularity is the square ports. I have an L28/E31 combo. I like mine and the car is certainly fast. I am running SU's, premium gass and so far have not had a denotation problem (I do have a mild cam which helps with the denotation). I am in the process of buildin an F prepared Z. I am using an l28/e31 combo. The head is shaved quite a bit, valves are larger, ported and polished, the cam is a stage 3 and the pistons are flat and 40 over. I am shooting for a 12.5 or higher compression ratio. The E31 is good for racing aplications but for the street it can give too high a comp ratio. I would like to build a P-90 head for the street. The exaust runners are supposed to be the straighest on any of the L heads and have the best flow. The head is supposed to have a very good quench zone too. Being that it was made for a turbo Nissan focused on the flow of the head. It would be a great stroker head. I would get the non hydraulic lifters though (P-90a).

[Arne]

You should also read up on Bryan Little's site, Z Garage for some additional information on heads and an L28 build up.

The link to Bryan's site. Good info there.

http://www.geocities.com/zgarage2001/z.html

[texasz]

Part of the reason for the P-90 and E-31 popularity is the square ports. I have an L28/E31 combo. I like mine and the car is certainly fast. I am running SU's, premium gass and so far have not had a denotation problem (I do have a mild cam which helps with the denotation). I am in the process of buildin an F prepared Z. I am using an l28/e31 combo. The head is shaved quite a bit, valves are larger, ported and polished, the cam is a stage 3 and the pistons are flat and 40 over. I am shooting for a 12.5 or higher compression ratio. The E31 is good for racing aplications but for the street it can give too high a comp ratio. I would like to build a P-90 head for the street. The exaust runners are supposed to be the straighest on any of the L heads and have the best flow. The head is supposed to have a very good quench zone too. Being that it was made for a turbo Nissan focused on the flow of the head. It would be a great stroker head. I would get the non hydraulic lifters though (P-90a).

From the research I've done the P90 is a great head to use but requires some modification whereas the N42 will yield the same results without any modification. Now this may not be the complete picture with respect to flow, quench, and all other factors; that may have only been with respect to a few of them.

Also you are mistaken in your above statement about the casting code for hydraulic vs non-hydraulic lifters. The non-hydraulic lifter head is the P90 and the hydraulic lifter head is the P90a.

The link to Bryan's site. Good info there.

http://www.geocities.com/zgarage2001/z.html

Thank you Arne, I didn't have the link handy when I posted.

[Arne]

I'm interested in this thread, as the 240Z I'm picking up tomorrow has an injected L28 in it now. I haven't confirmed it totally yet, but it appears to be an F54/P79 combo with the matching late 280ZX injection. I haven't decided for sure yet, but I'm leaning toward swapping back to SUs on it. We'll see...

[jmortensen]

I pretty much agree with zguitar. My L28/E31 setup requires 95 octane, but runs strong at 11:1 compression. If I had it to do over again I would have started with a shaved P90 and saved myself the hassle and $$$ of having to install the larger valves in the E31. I also spent many hours cleaning up the combustion chamber where a P90 would have required maybe 1/4 the time to get a better result in the end.

The nice thing about the N's is that you slap them on a flat top block and you've got a good compression ratio for a NA buildup. They really aren't the equivalent of the P as far as the chambers go though. They have been the head to have for a long time because of the ease of installation and the lack of modification to get a decent compression ratio, but for someone willing to spend a few bucks the modified P is the way to go. If you're really going all out then it doesn't really matter which head you start with, because you'll inevitably end up with something like this: http://forums.hybridz.org/showthread.php?t=104420 check post #12.

In the US the P90a was a hydraulic head, but some heads have been coming from Japanese importers that are marked P90a but have lash adjusters and not hydraulic lifters.

[axefreak]

I don't know to much about this stuff but I am trying to understand it.

I don't think puting a P90 head would require any modifications (sticking it on a none-turbo engine). To achieve a high compression you need to have flattop pistons.

Any modifications are only to achieve higher compression but are not necessary.

RIck

[jmortensen]

I don't think puting a P90 head would require any modifications (sticking it on a none-turbo engine). To achieve a high compression you need to have flattop pistons.

If you just stick a P90 on a flat top block you end up with 8.3:1 or 8.5:1 compression. Not exactly high enough for a hipo NA build.