I'm running a 15t Clutchbell on the HPI .28 and, I'm just as fast (if not faster due to driving ability) as the $400 engine guys (and, i run a little richer than most). I'm not sure how long of tracks you guys are running on but, I think the HPI .28 is more than enuff for any track - In fact i can't see why you'd want a different engine unless you were doing tractor pulls, have size limits or possibly wanted better fuel economy (the .28 is thirsty). Grant you: the midrange needle is a bit tricky to get right - 2 needle carb woulda been better. I'd say if you don't think the .28 that it comes w/ is enuff engine you need to work on tuning a little better! If you just have too much money and, have to burn it on something that has a big dollar name so you can sound fast - give me some of your extra $ so i can by the essentials and, still beat you! LOL