ORIGINAL: ProRCRacer88

From my experience with the RB 928, id stick with RB til i get out of nitro rc. They are a bit tricky to tune if you dont have the right plugs or run 30% in some cases. Everything else about their motors is grade A performance, reliability.From guys that are around me that run RB's, you couldnt sell them a different motor unless it was a novarossi. RB's also last alot longer than most other engines. That S7 will outlast that Vspec or any other OS for sure. I broke in my 928 by idling 5 tanks through it( shuting off after every tank to let cool with piston BDC) then running it very rich for another 6-8 tanks before messing around with the carb for performance. My other RB is the C6 BB7T L2G .21, which is still in the box for now until my buggy gets here and is rtr with the other stuff i need. Those 2 engines are the best of RB's offroad engines. For your budget being $300, id say go for the S7, Rb doesnt make junk, or nothing slow no matter what it is. Have no idea about sirio besides the leaking carb i have on my Sirio .27, and cant find a replacement for. Id like to get a novarossi one day or a ninja but for now its all RB for me.