The Great Planes Viper or out of production Lanier Preditiors are a popular choice, and are fine for learning with. There are some kits available too, if you had rather build it. The Thunder Tiger Pro40 ABC is the only approved engine, but it is the best choice of them all anyways.

The $100 claiming rule, huh? Yeah, but buying a used $80 engine for $100 may not be the best idea!! I can show you how to make your engine run like a champ, and it will be legal anywhere. Our district only allows 16,500 RPM with an APC 9x6 prop ready to launch. I can send you some information I put together for the pylon workshop/clinic which will tell you how as well as a bunch of tips to racing. Randy Bridge and a lot of others helped and reviewed the documents and will give you all the dirt on racing. Do I have any proof? You should have seen how tight the 424 class was after the workshop!! I think I might have messed up giving out all my tricks...[]

Let me know if I can help you