I agree with Vertigo's post. You will see a substantial increase in RPMs. As with any tuned system, you will have to make sure you are using the correct propeller. Since the UltraThrust is a fixed length tuned muffler, you will not be able to tune it to your favorite prop. You will most likely have to experiment a little to determine which prop diameter and pitch combination gives the best performance. I do not know whether Performance Specialties provides prop recommendations. A good tachometer is essential in order to truly know which prop is best. An accurate radar gun is even better.