I hear a great motor is the fantom FR 12, but it has the turbo head which i believe makes it not roar legal, turns it into a outlaw. The Diablo .12 is really awsome, u can find it on stormerhobbies.com for 65 bux!!!! This motor had the highest top speed at the nitro dirt challenge for 1/10. I also saw it in a mugen that a pro driver was driven, this thing hauls butt. I will be picking one up for my stadium racer as soon as i get a chance. Trinity Evo 2 is suppose to do pretty good, but a bit pricey, 200 bux. And then u can never go wrongwith an O.S. motor, awsome reliablility, great tune, long lasting and tructworthy, fast, everything u want in a race motor. The cvr and tr are suppose to be pretty awsome.
I strongly suggest the Diablo though, due to price and is still a hauls ballz motor. 1.25 hp, 34000 rpms. Long lasting, i was even told by the pro that he can usually get 12 minute run times with a 75cc tank with this motor. Goodluck