dewey

Is it possible to raise your compression ratio by replacing the head gasket with a thinner one? Enough to make a power difference?

eeterp

yes and yes. you can change compression with a thinner or thicker head gasket. However, I don't think you'd see much difference with a thinner gasket because our gasket is probably already fairly thin. Also, shaving the head should increase compression as well, but I don't know the limitations on this procedure.

JDMstuff

When you do any shaving of either the head or the block, you have to make sure that you have enough valve clearance. Otherwise, you may get piston slap and cause you a whole world of trouble.

kc5zom

Yeah. Why not get a set of pistons (or have some custom made)? They will be more reliable than half assed tricks like gaskets or messing with the head.

zeus

It doesn’t matter how one raises the comp ratio, the valves will always end up closer to the pistons (increasing stroke being the one possible exception). There is nothing wrong with shaving the head to raise compression, as long as it is well thought out. It’s also far more effective and easier to shave the head, cc the chambers and flow bench it to increase c/r and performance than changing pistons. Not to say that good forged flat tops are a bad thing, just that head work nets greater gains and you don’t have to pull the motor. To say that it’s half assed, is all wrong. I contend that head work, including shaving, is the preferable option. When’s the last time you priced custom pistons?

kc5zom

Last time I priced custom pistons they were $450 to lower the compression ratio. Of course the MazdaSpeed set available to raise the compression is less than $200. Anyway you have to be some kind of tard to want to take the half assed approach of weakening components of the engine to raise or lower compression as opposed to doing it the right way with a good piston upgrade.

ProtegeES

My bother changed the pistons in his GSR with B16 pistons and a thinner Mugen head gasket. The CR is like 12:1. It made a good difference in power, but I dont think the head gasket by itself would do squat. The thinner head gasket increases the CR by
just 0.2:1
His car now makes 190 whp N/A

eeterp

A thick gasket is not a bad idea if you want to lower the compression just a little bit for piece of mind when turboing.


12:1 compression ratio!?! what octane gas was he using?

ProtegeES

the car runs fine with 93 octane without retarding the timing. The car has a knock sensor so he would not hear it ping. We have checked the timing several times and it stays at 18 deg.
The Toyota Matrix and Celica GTS have a CR of 11.0:1. That is pretty high for a production car!

Tom Slick

your head is made of aluminum, you can't grind it. you'll have to use a fly cutter on a milling machine.

jmauld

These methods have been used for a long time to get more power out of engines. There's nothing wrong with it as long as you take the time to do it right.

You will need to measure the clearance between your valves and your pistons, if you're planning on shaving the head or using a thinner gasket.

You will also need to keep a closer eye on your engine temps, with material removed from the head, it will be easier to warp it if you start overheating.

Tom Slick

now i'm curious, how do you "grind" aluminum? are you actually using a grinding wheel or an aluminum oxide sanding drum/belt?

sorry to get off topic, but you have peaked my interest. i have never seen it done.

kc5zom

Gee, sounds pretty half assed to me.

marc38

Grind your head will also retard valve timing.

Tom Slick

thanks for the reply on the "grinding." i still don't see how it would work, but i believe you. i guess i'd just have to see it done.

you would need adjustable cam pulleys if you want to get the cams back in spec. it doesn't throw timing off that much, but if you are going for performance, you 'd need the pulleys.
cyl. heads are shaved all the time. it is the only way to repair a warped head. it isn't half assed, it is an accepted practice in the repair/machine trade. it is easy for any machine shop to clearance your pistons/valves. it just involves a cutter and a little bit of measuring.