How to increase compression

[GodSquadMandrake]

I had another thread where I was trying to figure out my compression ratio, and it's too low! I only get 7.66:1. The engine is an EJ22 with EJ20G heads off an 89 JDM Legacy, those come with the big 57 CC combustion chamber.

How much could I safely shave the heads? .020"? I know I can put on a thinner cometic head gasket, but I want to get at least 8.5:1 and I don't know if I can get that much out of a thinner headgasket.

I'm planning on running E-85 and this motor will run a 34MM restrictor per Rally America spec so I need more compression to bring up the low end torque and make the most out of the little air that that restrictor will let through. I know a 7.66:1 motor is good for high boost, but that's not good for a rally motor where the top starts to drop off around 5,000 RPM.

What are ways to bump the compression up?

[93forestpearl]

What shortblock is it? If it is a turbo shortblock, you could maybe use pistons out of an N/A motor. I'm not sure how the dish of the N/A pistons compares to that of the turbo pistons.

Subaru states the surface griding limit of the heads is .004" If you take .020' off each head, you can possibly start to get into fitment issues with the intake manifold especially if you are running significantly thinner head gaskets. Also, your cam timing will be off slighly.



Personally I'd look into some 2.2 pistons with less dish to bump you up a bit.

[GodSquadMandrake]

I have the closed deck turbo block and EJ22 Wiseco pistons with -20 CC dish.

[PhyrraM]

Really there are only a few options and you've listed most.

Smaller chamber- weld material in, shave heads (w/ adjustable sprockets) or choose other heads (WRX EJ20G?).

Thinner gasket.

Smaller dish- N/A or custom pistons.

The easy choice, for me, is to spring for custom pistons.