or a stock gsr turbo...i talked to mtber about this..cuz i was about to buy a stock gsr bottom end..and turbo 10psi..and he said that its very possible but eventually the cast iron pistons will fail..so if u using stock pistons..itll work..ive even seen a dyno of a gsr stock at 13.5psi..but the reliability isnt goin to be worth it in the end..if u have forged internals..then..id think no higher then 10.5:1 would be ok for atleast 10 psi..