i was talking to a guy at the track and he takes a v-spec and puts all ninja parts (crank, rod, piston and sleeve) in the v-spec case and all. he said it has more power (it looked like a TON more power) and also better fuel consumption. he was pitting around 11 min in a buggy.
but i think if you put a crank in it you'll have to put the ninja rod also but i may be wrong about that.