Originally posted by e30dood
The y8 head has a smaller combustion chamber than the z6, this why it has a slighty higher compression ratio. If you want to raise compression even further, use a6 pistons.
What you can do though is use a y8 head gasket and remove the middle layer to bring your compression ratio up higher by a few tenths. Or you can do that with a z6 gasket too, I heard it also has three layers but I can't confirm this quite yet.
Btw, don't consider raising your compression ratio though if you plan to turbo.
The y8 tranny has steel shift forks instead of aluminum ones that the z6 has which wear out easier.
you wouldnt happen to have that thread from H-T.com on all of the d-series parts and pictures saying what to use???