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Discussion Starter · #1 ·
I just read a post where Bob H advised against using the p90 head in an N/A engine. This perked my curiosity, as I was intending on putting a P90a head on a f54 NA block eventually. Mind you this engine swap is at least 9 months away for me, as I need to do some other things first. I was waiting to post this question until later, but my curiosity can't wait any longer.

I understand that the p90 head chamber is bigger, but I was probably going to use higher compression pistons to raise the compression ratio to about 10 to 1. With 10:1 I should still be able to run 92 pump gas, and it should have the amount of power I was looking for. On Bryan Little's site, he talks abit about the 90a as having the hydralic rockers (lash pads?), and my local Nissan dealership and he confirmed that the heads had different rocker part numbers. I thought that sounded really cool, and Bryan said the engine was really quiet, which I like also.

Anyway, anyone using any p90, especially the 90a on a NA engine, please let me know what your experiences have been. Also, anyone who has either found or ordered higher compression pistons for the L28 block, I would appreciate any info.

Thanks to all, on the best Z board on the 'net.

jA
 

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Discussion Starter · #2 ·
i have a 78 280 w/ a p90a head on it. i have no real experience in Z's and when i bought the car it had the head on it. as far as i know the biggest advantage is that the head has square exhaust ports which supposedly flow better than the ones with the cast-in liners
i wil say that with the head on the car the power does seem to go all the way to 6000 rpm's before dropping
but that's just my limited experience and it may not be actually any higher, but that's becasue i haven't ever had a "normal" head to compare it to. (which would be the N47)

my two copper coins worth.
 

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RE: I have a P-90a

Let me clarify what I said before, and it might be clearer why I don't advocate the P-90 series heads for a normal N/A motor.
First, I am running the P-90a on my NA motor. But there is one important distinction, I have a 3.1L motor, ie more displacement, so the extra chamber volume is to my benefit. My compression runs about 10:1, where with just a 2.8 motor, it would be about 8:1.
Now, if you are looking at buying special, ie domed pistions to up the compression, then this becomes a moot point. You can't raise the compression otherwise without shaving the head a serious amount. I don't know if the mod that Bryan outlines for the P-79 will work on the P-90 heads. It seems like it should, but I don't know what is different btw the heads.
Now, to address the hydraulic part, yes, they are definatly quiter. And you no longer have to adjust the lash every so often. It is really great. But, they are a wear item, and they will wear out with time. And they are not cheap to replace, $42 each with the IZCC discount through Courtesy Nissan in Texas,(about the best deal out there). And with the potential to replace 12, that gets expensive quickly.
I address the P-90 head extensively on my web page,(I am still working on the re-write, but I put the old page back up). Here is the link.
http://www.geocities.com/motorcity/track/6997/

If you want 10:1, there are a lot cheaper ways of getting there. I would reccomend an N-42 or N-47, both of which are good heads. Some say the N-47 is not good, but with some small work, it is great,(I am outlining some of that on my new head page, which is not up, will turn some heads to new ideas, just as my using the P-90a did). Bryan's site is an excellent starting point, and his proof is in his most recent time slips, which nearly match mine when it wasn't running so hot,(all fixed now).
-Bob Hanvey
 

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Discussion Starter · #4 ·
RE: I have a P-90a

Thanks for the post Bob. I just started checking out your web page and it looks pretty cool. Right now I'm still in the "dreaming" phase of my engine rebuild, thanks for all the info!

(That 3.1L engine thing is looking pretty good so far..:)

jA
 
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