Heheh, I have run a few TRX2.5s, an OS .18, and an XTM .18 in my rusty. The OS is the most powerful(but also the tightest fit), the XTM .18 is much more powerful than the 2.5(just wait till I port the sucker!), and all the TRX2.5s crapped out on me after a a gallon or two. I used to be a huge supported of the TRX 2.5, but after running different engines in my truck, I'm never going to even touch a TRX 2.5 unless it's selling for $25. It isn't really the engine that makes the rusty so fast, it is more of the FD ratio. If the X-Cellerator had the same FD ratio as the rustler, I know it would be faster.