which is the largest engine that will fit in the volcano. is it .21? and from avalanche or traxxas? oh and i also found a toki 27cxp for $59. will it be worth ? does it fit? there's also a toki .21 for $45.

I'm not really sure, but whatever it is has to be small-block, and anything more powerful than what's in there will shred the driveline (strip gears, rip dogbones, break diffs) and will end up being less fun than its worth. Also, CXP engines are terrible, they are the same as VX engines and Redcat got away from those for a reason. Go with SH if you want to have a good, cheap engine.