The tweeked manifolds will give you as much as 80 ft lbs of additional torque between 1700 and 2500 rpm. Amazing but true. It wil give you an extra 10 or 15 whp at redline all dependent on getting a custom remote dyno based tune. These were my results. In addition, the car acquired a much more deep throated satisfying growl in the low to mid rpms. I have a stock exhaust. All that said, sooner or later you'll want the wavetrac.