Answer
I doubt youd get 1/2 a horse.. the srt4 has been tweaked to get all the cheap power out of it. this is an issue when you buy a budget performance based car.. its not unusual to hear about people spending $4000 on an exhaust system for a s2000 and actually lose horsepower.. its a performance based car, and the engineers got all the power they could with their budget.the only noticeable performance upgrades will be internals/turbos.