I thought the TRD gaskets to suit the 20v were .8mm, not .5mm. When changing from standard to trd gaskets without shaving the head or deacking the block you will end up pretty damn close to 11:1 .
Sam is indeed the man - From what he told me - The blacktop and Silvertop have very different combustion chambers. You can only guess that Toyota made particular changes to the piston crown and the heads to deal with the higher compression in a certain manner. I will be shaving my s/t head the very min, and only if required. I would suss out whether that gasket is the trd 16v or 20v one too.
