3DMike - realize that if you tune the header (by cutting it) so that it is 1/4" to 1/2" longer than you would for max. RPM, you push the power band down more into the midrange RPMs, where you want it for a Fun-Fly. A header and tuned pipe will not effect the throttle response, in fact by pushing the power band down, you can 'get on the pipe' quicker and throttle response is better!!!