It's common sense to run the o.s. .21TM, because it's a drop in motor. But man, that's a heavy price tag. My 3.3 is great but just doesn't hold a tune like a o.s. motor does. There isn't anything wrong with my 3.3, I just like to see what other options there are. I know the o.s. .18tm is D/C but wonder if there are other o.s. motor that will fit with some minor tweaking. I'm really open to other brands and options. I just favor o.s. because I had a o.s. .18 before on my tmaxx and it was great, tuning was easy, held idle great, and ran like a champ. If somebody can point me to the right direction with an affordable budget I would greatly appreciate that. Thank you!