i was also wondering what engine to buy. i have looked at the fantom .12 engine. this engine should fit. not to sure about the crank though. haven't really looked. anyway, i think the mach .15 engine is a good engine. my question is, if they don't allow .15's in sanctioned race's, then why did they put one in the xxx-nt? it's all a marketing scheme. now you are forced to buy a .12 if you race in those. the track i race at doesn't care. which is nice. although, i would really like to get a new engine for it. i really like the xxx-nt. i have changed set-up from stock. basically, all i really did was put red springs on front with yellows in the back. BIG difference. everything else is still stock set-up. i also was thinking about throwing the mach .15 on my t-maxx. any thought's?