Finally im getting on top of this EFN 202. Pistons used were RA3302, which have 7.2cc dish and sit 0.035 down the bore. It's a 40thou over 202 (3.665) and the new head i have (YT modded 161) has a chamber volume of 50.6cc according to the guy who cc'd it for me. With gasket, this would give me 8.9/1 compression acording to this: http://www.csgnetwork.com/compcalc.html

That calculator, by the way, came within .1 of the Dyno2000 software used by my tuner.

So i made 102rwhp at 5000rpm with the same motor, but my open chamber head (shaved 0.030) which i ported and has bigger valves, but not as big as the YT. And it was running rich. Not too bad?

Now, how do we get comp up considering ACL has run out of 40thou flat-tops (more on order) and i'd prefer not to strip the motor for new pistons anyway.

How can i tell how much i could take off the head safely? Would this acheive what i desire, and that is comp around 9.8/1 or 10/1 , which is what the 2cc dish or flat top ACL piston would give me.

Thoughts are appreciated.

I had a VK 202 head took 40 thou off, which I calculated gave around 10:1, but my maths is not that good.
If you go over 40 thou I was advised by Crane Cams the rocker angles will be excessive (stock EFI cam) so not advisable unless you want to go into modifications there.
if you take material out of the head chambers you will actually be lowering compression, not exactly what you want I think.

Cheers. I know decking would do it, but trying to avoid pulling the motor down, its a daily car at the moment.

John, your VK would have had non-adjustable rocker gear. This 161 head has adjustable so i think it gives me more leeway before running into valvetrain problems? And you may well have got 10/1 with a shave if you went up from stock compression. The pistons in mine dropped comp from 9.4/1 (standard 202) to 8.9/1 and thats what im trying to recover.

Edited by user Thursday, 19 November 2009 10:03:15 PM(UTC)  | Reason: Not specified

Ah of course, itll affect the angle and result in the contact point moving rearwards a tiny bit. With the 40thou, plus the small amount it was shaved originally, hopefully we wont have any problems. Worst case, i had to run lash caps on my current head until i bought adjustable shaft mount rockers. It was fine with the caps.