Compression Ratio Question

[asshanson]

Edit: I misread. If you are asking about the benefits of compression, more compression will net more power, but will be more prone to detonation. If you are running E85 or high octane fuel, there is pretty much no worry. See below

The turbo has nothing to do with static compression, only dynamic compression under boost which is difficult to measure. It's a math function of how much base compression you have plus the boost pressure you're running. So going from 7.8 to 9.0 will give you more compression all around, and you'll see more power too. So you would normally have to compensate in the tune, with maybe less timing and less boost. BUT since you are going E85 the 9:1 compression is pretty safe, and you can likely do more timing and boost.

In any case, going from a 7.8:1 piston to a 9:1 piston should give you better all-around driveability, but definitely get a dyno tune for whatever boost level you plan to run. Fortunately E85 should be pretty safe.