I have a Ripmax Rapier with an OS 46 FX, stock muffler. I have been running a 10x6 on it, and was advised to use a 10x8 prop. What do you guys suggest using on my configuration? I am just getting into speed planes, and I can see where it would be addictive. Thanks in advance.

APC 9x7 - 9x8, it is not going to be much faster, (although pretty light, the Rapier has a fairly thick airfoil); But thats about the best yer gonna do...

To get any more speed than that yer gonna need more horsepower to turn more rpms with the same or higher pitch.

A 10x8 prop will just load the motor's rpm so far down that it will never get into it's peak H.P. range...

ya, a 10x8 is way too steep. I have spent alot of time tweeking props including cutting them to get custom sizes for a stock 46fx and ended up with an apc 9x7 being the best. Better vertical with the 9x7 over the 10x6 even.

I tried down to an 8x8, but is was slower and had less climb.

An apc 10/7 cut down to 9 1/2 works for me.