ok here is what I got, Four Star 60 Ive got an OS 91 FS in the nose, Heres my problem, a guy I fly with also has the 4*, with a Magnum 80 four stroke. his four star will do circles around mine, it seems to have more power, and it is alot faster than mine, Im swinging a 14x8 prop, and this is the only plane that this engine has been in, why shouldn't mine out perform his?

You have your plane proped for pretty good all around performance. It probably has pretty good vertical.

The pitch of a prop is the ideal distance it will move forward in one revolution. With your 14x8, each revolution moves it forward 8 inches, ideally (there are losses due to slippage). If you want it to go faster, you need a higher pitch prop. When you go to a higher pitch at the same diameter, the engine will slow down and lose rpm's and maybe speed. It, thus, becomes necessary to reduce the diameter to keep the rpm's up. As you reduce the diameter, you lose thrust. Thrust is what gives you vertical. At some point, the thrust becomes lower than the weight of the plane and that causes problems in taking off and maintaining normal flight.

If what you want is speed, a 13x10 will turn about the same rpm and produce more speed at a cost of thrust and vertical.

You need to watch the rpm's and not over rev the engine when your playing with selecting a prop. The "redline" on your engine is about 11000 rpm. That is unloaded, in the air. On the ground, with the additional loading of being held still it will turn about 85% of the rpms it will turn in the air. In other words, if you tach the engine on the ground, do not let it exceed 11000 x 85% or roughly 9300 rpm. This is not perfectly accurate, but a guide line. Error on the low side so as not to over rev the engine in the air.

Also, keep in mind that every plane will have flutter at some speed. If the plane reaches that speed, there is a high probability that it will not come back in one piece.

The 13x10 will probably produce the results you are looking for.

Also, try a Graupner prop. They are fabulous on 4-strokes

I use a 13x9 - 13x10 APC on my Magnum.91 powered Extra300. It takes it out of sight vertically, and it's decently fast at that too. I might suggest your a tad over-propped on it. I've just found the APC props deliver the most power-to-$$ ratios. Really they are the best that I've tried, and got it down to the 2 I mentioned. Good luck, and I hope you get it propped, and go fly circles around your 'bud.

thanks for all the replys, just placed an order with Tower!!! don't tell the wife