I guess it depends on the engine you have in the 8th gen Si. If it is a K20Z3, it has 11:1 compression ratio. Be careful how much you boost it! No matter what, you will need a new tune. That means getting a Hondata Flashpro or other, and also getting it on a dyno with a tuner guy that knows what he is doing. Check out those additional costs. Don't blow up your motor.