OK, for the hot rodders. In our racing class one of the engines required was the OS .46 FX. By milling down the head with a wet dry sand paper on top of a glass sheet then taking tach readings over and over until the RPMs raise then start to drop you can gain a little. By using the burrs on my dental hand piece I could smooth out the ports and do the same thing and get a little more. Is it worth the time and trouble?? No. You could also destory an engine doing this or just make it worse then it was. A MACs Exhaust system will add some more beans but at the cost of over 40 bucks. A hand full of good APC props and doing some flight testing is a lot cheaper and teach people what the correct prop on any given plane will do. If all out speed and power are required then there are a few good engines like the Jett to start looking at. The price of some props or a bigger engine is just a good idea unless you plan on going racing. RPMs don't always equate to power, in drag racing we shifted at the peak power band, not the top RPM.