If you'll do a search someone who is developing a turbo kit for the car made a stainless steel head gasket that lowers compression into the 9:1 area... It was just posted a few days ago

 

One of the problems with extra thick head gaskets is that they change the combustion dynamics of the chamber. The stock S2000 pistons actually come "out of the hole" by about 0.020" from the factory and this helps contribute to improved quench/squish area with the factory open chamber head. Quench actually helps improve mixture motion and reduce the potential for detonation.

Caveat emptor.

UL

 

I think what UL is trying to say is that the ideal way to lower CR is with pistons or CC/valve shaping such that the quench chars aren't affected much.

That said, I would not recommend a novice try and "combine" layers of the stock gasket or stack them; I would recommend a solid copper or MLS gasket that is specifically made for this purpose.

For calculating the change, this may help:

http://www.marcuccimotorsports.com/resourc.../head_calcs.xls

I came up with it and the numbers that are plugged in are either known or measured S2000 stock. Putting in .064 for the gasket (double thickness) and I get a .88 reduction in CR. The preferred method would be deshrouding and a little more dish in the valves which would eliminate a few cc's from the CC which would have the same effect. A 5cc average change in the CC volume will have about the same effect.