rule of thumb for a c/r increase is that you get 10-15% of your power per point of compression. so if you are making 120 on the Z6 at 10:1, and you bump it to 12:1, you are looking in the 140-150 range. but, you will also be able to take advantage of that higher c/r by getting a bigger VTEC cam, which could be another 5-10 horse, depending on how wild the cam is.