The straight pipes offer no back pressure, so yes you have more power on top end, like a drag racing car. you also lost power on the bottom end, but may not feel it so much. As for rejetting, you may want to take it to a shop and have it evaluated by them. At worst case you may be lean at idle to mid range, and can richen at the A/F setting on the carb to offset that. At least that what we did when we were drag racing.