RE:
The AX series engines are basically just sport engines for general purpose usage. There is nothing wrong with them as they were designed for ease of use, good performance. But not high performance. If you want performance, speed, power, etc. you need to go with a performance engine. Something like a Rossi, NovaRossi, Picco come to mind right off the bat. Jett is the ultimate in Performance. For price though a Evolution .60 NX is a good one that has sparkling performance too, especially if you use the special Evo high performance tuned muffler that Jett designed for Evolution. The Evo .60 NX was designed to give good performance. Guys liked using them in the wicked fast Jackal RC plane too. The Thunder Tiger engine is maybe another decent engine that might offer good performance too.