Why do you want more power? Is the car slow as it is right now? I bet you might even be pleasantly surprised with a rear gear change. Figure out what your car has in it. Then worry about power.
I'll also ask this. Have you ever been in a 12 second street car? Have you driven one? If you haven't, hangout with some of the local car guys, see if anyone will give you a ride in their's. Everyone loves to think 12 seconds is slow. But to put it in perspective, a low 12's car, hits highway speed from standing still in 4 seconds or less.
