I've been using the apc 15.5 X 12 4 blade for a couple of years on a jupiter using a bolly muffler. It's a very light plane and the 4blade really smooths out the power. I used the 17-10 on my Focus (again on the muffler) with good results. The 17-10 on the jupiter has noticeable improvement in thrust, but it also makes the plane "jumpy" on throttle application.