Well, there's the Epic 18 and the orion 18 and I believe the new OS 18 are all side exhaust.
From what I've read, the Epic is a powerful engine. I have the orion wasp 18 in my SportMaxx. It's not bad, but it could be a little stronger. As for the OS 18, I don't know. I do know that my LHS guy (good guy) had installed it on a xxx-nt just to see how it was. He said that even during break-in, it was wheelying so much he couldn't drive the thing.