[C. Ludwig]

ITBs aren't going to give you much, if anything. The big bottle neck with the NA engines is always the exhaust. If you're running a silencer in the tail pipe as you described, it's knocking down a good deal of top end power. Very hard to make NA power without having a ridiculously loud car.

ITBs should give you a little crisper throttle response, if setup properly. Maybe a couple HP up top, depending on how everything else is matched. Probably lose a small amount of power through the low and mid range. All in all, I would be surprised if you saw +/- 5 HP anywhere in the curve.