He'* got the stock 2.55".
Nobody has ever dyno'd to determine actual gains. It'* always been based on flow, or ratio'* as compared to the S2.
The 2.2" is widely believed to be UP TO 25hp and 40 ft/lbs. The S1 seems to respond a little better to pulley changes due to the better EM design as compared to S2, and the fact that our SC spins up a bit quicker.
The 2.3" would probably be 15-20hp and 30ish ft/lbs based on this. But again, this would be on a perfectly setup car with mild mods already, and we have nothing concrete to back it up.