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hello friends glad i could catch your attention, im looking to increase the compression ratio w/o swapping cylinder heads/ block. I heard that 2002, e12, and e21, could have there compression ratios increased because the diameter of the heads are relevantly suitable for the increase. has anyone tried this? what was the outcome and if it was a good thing to do, how do you go about doing it?

thanks for your time,
happy holidays

You won't be increasing compression without swapping something out! Pistons/block/head/rods/crank. Something has to decrease cylinder volume to raise the compression. I have no idea what configurations work and what don't, but there's no magical compression knob.

Also funny topic heading haha

JodyStevens wrote: ...there's no magical compression knob.

Seriously? Then what's that wobbly thing between the front seats?

M30 heads are all about the same, with the exception of B35 heads, so swapping a head won't make any difference. To increase compression you need pistons. Sorry, just the way it is.

The heads used for cars with the 4a1 carb are different, but I am not sure if the volume is smaller. I my case, I noticed that the shape of the combustion chamber of such a head was mirrored, and the head interfered with my pistons because of that.

You can experiment with pistons though. There are differences there.

Mike W. wrote:M30 heads are all about the same, with the exception of B35 heads, so swapping a head won't make any difference. To increase compression you need pistons. Sorry, just the way it is.

There was a thread on E12 group on FaceBook where someone came up with M90 head that had smaller combustion chamber volume.

I'll be damned if I can remember details.

My head(ache) story is over here:
http://www.firstfives.org/bboard/viewto ... highlight=

I also posted on facebook, here:

Just wondering. Can't a standard head be machined (is that called "shaved") to reduce the final volume and this would increase the compression ratio?

Jan