What is a head shim?

[tkuss]

Hey guys, I don't know anything about turboes, just wondering what a head shim is. Seems to allow you to run more boost when keeping your engine interals stock. So what does it do.

 

[Sapling]

It is a shim that is added under the head to lower compression. Lower compression allows you to typically run more boost per octane of fuel with out the dreaded detonation. That is the general idea.......

 

[rxrider]

It acts like a thicker head gasket, s
head shim is way better than stacking head gaskets.