Hi, I have a P90 and I would like to shave some to get higher compression. Could anyone tell me how much I could shave off to not have to require shimming. Byant littel site has it where he shave .080" and i think he required shimming.
Has anyone removed and chain link or washer behind the chain tensioner?
Thanks

 

The Datsun valve geometry is VERY sensitive to any head dimension changes. What is the current hardware in your engine, what comp ratio do you have & what comp ratio are you after?

Ben
Adelaide,
South Australia
IZCC#1902
240Z L31ETT on-the-build
L28ET MR30 Skyline GT
FJ20DET DR30 Skyline RS-X Turbo

 

Ben right now I have a stock F54, flattop block, stock P90 head, and am using a felpro gasket which makes it right around 8.71:1. I'm in california and want to push the car to the max limit of 91 octane. I was shooting for something in the mid 9's to 10. Bryan little site has a lot of details about milling the head .080" and using shims to trick the engine. I think I will try to go that root unless someone here has another suggestions.
Thanks

 

I'd recommend using a standard N42 (or any other 44.6cc head), which will give you 10.08:1 & 0.03mm deck height (which is the same deck value as you have now). If that's too much you could fly-cut the pistons 0.25mm (9.83:1 & -0.22mm deck), 0.5mm (9.59:1 & -0.47mm deck) or slightly enlarge the combustion chamber (which would be a good idea for detonation prevention).

Of those 3 suggestions, doing the chamber mods is the best, as it is keeps all the compressed charge in the head volume, not the cylinder.

But they all allow you to keep the standard head height, and therefore avoid the requirement of cam-tower shims, different lash pads & lost of measuring.

Ben
Adelaide
Sth Australia
IZCC#1902
240Z L31ETT
L28ET MR30 Skyline
FJ20DET DR30 Skyline RS-X

 

I'm with Ben with recommending the N42 head. This is one of the more favored heads for instaling onto L28's for a higher compression. P90 is a great flowing head but its meant for a turbo block. The only other engine I see it commonly used for is 3.1L Z's

Bob Havney has a great page talking about P90's. I don't have the link right now it might bein the ZDriver.com links. Let me know if you need help finding it.

zya
ZDriver.com
<a href=http://strictlyz.com>StrictlyZ Store<a>

-Have you had your daily dose of Vitamin Z?-

 

Thanks Ben,
I will hold back on the P90 and possible go with your suggestion. The thought of loosing my timing is kinda scary to me. Another question then is if I get a N42 about how much would it be to get new steel seat installed, has anyone done this recently?

 

Here in Aus. all late model N42's had the hardened steel seats. But any competent engine shop could do it for you. Everytime I've got a new head, I've had it checked for cracks, straightness & had the valves re-lapped as a minimum. If you are going with the idea of increasing chamber cc's, then you'll want to get the seats removed/replaced as part of that process.

I get all my engine work done at my local 'Repco'. They have complete rebuilding facilities & have done a lot of Datsun engines. But I'm afraid that I can't really recommend any shops in the US, as I've only dealt with a couple & heard of a couple more. Ones that come to mind are:
Sunbelt Performance
Rebello Racing
Malvern Racing

You might want to post to some other forums to find a workshop near you.



Ben
Adelaide
Sth Australia
IZCC#1902
240Z L31ETT
L28ET MR30 Skyline
FJ20DET DR30 Skyline RS-X

 

Here is another choice. You don't say your intended engine use - if it is a street engine, I like the 83' Maxxima heads. They fixed the detonation problem on Z heads with a heart shaped squish area, and they are low cc heads for high CR.

Their only down side is smaller vales and exhaust liners. Some people think the exhaust liners are no big deal. If want max hp the bigger Z valves will fit in the heads

 

Guys, I have changed and went with an N42, mild port and polished, 3 angle competition valve job on steel seats, and unshaven. It will be going on the L28 flattop now, thanks for all the suggestions. For a while there I kinda got lost in the head combo thing, wasted sometime, and headache.