For whatever reason, the Twister series doesn't have too many fans. The MECOA site specs on the engine give the same bore and stroke as the classic 6550, but recommend a different prop (12-8). I could be ported to swing larger props at lower RPM and people are trying to get high RPM on an 11-6 or 11-7 - who knows.

The 55AX has lots of fans and some of the numbers being posted are impressive. I was not impressed with mine. I wasn't getting near the RPM as other people were claiming so I sold mine figuring I had a lemon.

The Evolution .60 is reasonably priced, has good reviews, and is slightly lighter than the 55AX.