I'll give you a for instance...my old tour was at the shop 2 days ago. It's a 2.5 with 9:1 pistons and kinger heads, so the compression would be like 8.8:1. It did 325 to the wheels at 12psi with 91 octane crapoline. A 3L you can basically add 50hp to the equation would be my guess. If you have 93 octane I'd do 9:1 with or without the heads done.
