I modified my Evolution 26 GX with a carburetor that is the next venturi size up, this combined with a tuned pipe has resulted in a notable performance increase, This 26 has always been a good engine, but my altitude is always a detriment. It's in an Ultrasport 1000 so I was forced to use a 3 blade propeller due to ground clearance issues.

I'm currently at 5400 feet elevation, 91 octane ethanol free gas, synthetic oil at 40:1, Master Airscrew 16X10 3-blade. I'm getting 8160 RPM static, which is slightly richened from peak RPM. I may need a larger fuel tank, it emptied a 14 ounce tank quite a bit sooner than I expected, but more than half of this run the engine was on the rich side. I'll have to do more testing, but so far I'm liking it!