ok,i have one of these big cats on a plane i bought,that is giving me fits. i am missing an honest 1000-1200rpm. the engine has been taken apart and cleaned,inspected,reassembled,great compression,anyway,before and now the engine still won't turn the upper rpm it should.i am running byron's ST 10%/15%oil fuel,an o.s. type "f" plug,and i am only getting it to turn a T/F power point 18x8 6800-7000 rpm,and it turns a 20x6 zinger pro exactly the same rpm. do these need a substantialy larger fuel line and a drilled out clunk in the tank?or am i doing something wrong? i have the needles set to where it has a great 1400-1600 idle and raps up from idle to 6800-7000 in the blink of an eye. i can even let it idle for a couple of minutes,and hit it wide open and it has almost instant throttle response. so what gives? any ideas? thanks.

Different brands of propellers can give you dramatically different performance. Blade shape, airfoil type and thickness, trueness of pitch, and the materials it's made of all affect how a propeller performs.

We once tested a variety of props that were all supposed to be the same diameter and pitch. We got very different full-throttle RPM measurements.

On an O.S. Max FS-120, a variety of 15 x 8 props got turned anywhere from 9,300 RPM to 10,100 RPM, all on the same engine.

If you're engine's running well, then the RPM you get is OK.

On our test stand, we've run an 18 x 10 APC prop on a SuperTigre S3000 and expect low to mid-8,000's with a SuperTigre muffler (not very restrictive). We'll be using Omega "Super-T" fuel on a well-broken-in engine.

you may want to make sure that your fuel has no more than 15%
oil content. the s3000 owner's manual stresses the fact that oil content higher than 15% will degrade the performance of the engine. also you can try adding nitro to your fuel as the owners' manual suggests this, too.