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P90 Head Porting realizations

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whew. i know we're supposed to be patient, but nearly 8 months? man...it's a good thing the machinist i'm going to is backed up too...


Has it only been 8 months :-D

He did call me about 3-4 weeks ago and tell me he was at 235cfm on the intake ports, but did not give me the lift value. He said the velocity had improved over stock at that point and he would continue to 245cfm and then stop. BTW, this was with a modified E88 head. I figure 8 more months and he will start the P-90 head I gave him :?

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  • 1 month later...

I figure I should put this baby to bed. My buddy called me to give me an update as he is having his motor built by this guy. His E88 got to 235cfm or so and he never did start my head. My buddy is so pissed with this fellow I suspect I will not get any results from him. At some point I should go and pick up my stuff(chopped up P90). Sorry, some things are just too good to be true!

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I'll let you know within the next 6 months (I hope!).

My P90 was benched as flowing enough for 313HP at 28"

(inlet was 192.3CFM @ 0.450"' date=' exhaust was 129CFM @ 0.450")

This was with stock valves, but the valve seats are cut wide.[/quote']


Hi Ben,

This is great info. Is your P90 head ported or were these numbers with a stock head?


I'm curious, if stock P90 head can flow enough to support 313hp NA what horsepower would it support under boost? Anyone have a formula that might help with this?








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Oh, it's ported alright :-D

That HP figure is the NA potential, but it isn't 100% accurate - try googling for the way to guesstimate this value. It should be another matter when I force feed it via my ported inlet manifold!

The person who got it done was very impressed with the flow figures & he has a race L24 that is pushing out 160kW at the wheels using SU's at about 8000rpm....


The inlet efficiency got as high as 85% at 0.600" & 80.5% @ 0.450". Exhaust was 93% @ 0.600" & 90% @ 0.450". These figures are @ 10" pressure, with 44mm & 35mm valves respectively


The air-speed was 330.59FPS 1" down-runner.


I hope to have this engine assembled within 3 months.

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  • 2 weeks later...



Hey... before we just let this die...


I'm sure we could find another shop to continue the testing.


Here's a list of all companies in Florida with a Flow Bench (Super Flow)...


Wanna start calling a few? I'd be willing to help...






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  • 1 month later...



i just got my e31 head from sunbelt, am putting it on tomorrow.


the printout i received showed the following data:


stock (head before any work) port flow:


.425" lift...........158.9 cfm...........110.2 cfm

.525" lift...........163.5 cfm...........118.4 cfm

(.525" lift never reached with the cam i had in it)


final port flow:


.425" lift...........180.6 cfm...........129.3 cfm

.525" lift...........201.6 cfm...........145.1 cfm


according to sunbelt, 200cfm by their flowbench (flow pro) is 225cfm by anybody else's (super flow).


the cam jim set me up with has a lift of .520, and powers from 3500 - 7200. i think the duration is around 280. this is the max lift (valve-piston clearance) you can put in a 3.1 stroker without cutting valve reliefs into the pistons (using a 2mm gasket). the stroker kit produces a positive deck height of .025".


hopefully i can dyno the car this week and let you know what this puts to the ground with a 3.1 LD28.


i have pics, but won't post until i have guidelines since i remember john coffey saying something about sunbelt not liking that. john coffey, my 3,4 exhaust ports do look "funny" (but why do that only to cyl 3 and 4?)and i have single springs.



all in all, i'd say ~225cfm per cyl is pretty damn good for an e31...i cant wait to hear and feel it!

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  • 2 years later...
Guest 280ZForce

I know this thread is a few years old, but I'm trying to have some extensive head work done to my p90 head that is currently being machined.


And I went ahead and sent over all of James' pics from page 1 and his explanations on them.


I'm going to see what they think about doing this to my head, although I'm on a deadline with this head, they are a highly reputable shop that builds engines all the time for SCCA, IMSA, NHRA, NASCAR, etc.

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  • 4 weeks later...
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Doesnt matter what you do to the engine.if the head flow is stock,your wasting time and money.ive seen guys build vary expensive stroker setups and come back with 165whp...ive seen some do similar setups but have a extremely worked over cylinder head put down 260++ whp on 93 pump gas.the power with these cars is all in the head.porting an old maxima n47.then ill get it flowed.I like this head because it is a great street/budget race head.one day ill get me a p90:)

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While we have this ancient thread bumped...


The head cross sections are awesome to study and compare. I missed this one way back in '03.


I would like to mention something to correct a misconception for anyone else reading this thread in the future. Maybe I'm being pedantic, but the O.P. completely neglected including (subtracting) the diameter of the valve stem from the valve seat throat. The effective diameter ends up being around 1.391" versus the 1.525" mentioned, assuming a 5/16" stem. So, it's not a huge mismatch between intake port and seat at all. Sixteen thousandths, not fifteen hundredths. That number is an over simplification, but a decent ballpark.


Back to our regular scheduled programming...

Edited by Sven
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  • 4 weeks later...

I'm actually wondering what the conclusion was for ideal porting on intake and exhaust side. In these 6 pages I didn't read a conclusion and it's like I'm waiting for the last note to be played to conform port potential. ie, X Compression, with Y Head number, ported to Z dimensions produced this much torque with supporting mods. 


Really hoping to have a head job in the next several months done and aiming for 240-270lbs of torque at the wheels. (I find I don't care about peak hp, just a nice, healthy, mild torque curve)


Any conclusive data or directions?

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