I am pretty shure it will be a trx 650 from the xr 650. That seems to be the most reasonable engine to use.

 

i dont know why everyone needs to compare the raptor to the 400ex.if everyone doesnt recall the 400ex got the high performance quads starting to be made again. also everyone used to say the banshee is better then the 400 when the banshee could only beat the 400ex in a drag. Also if u race the 400 and the raptor in the woods the 400ex wins easily. anther thing is the axle bends very easyily on the raptor and which yamaha shouldve put a little more time into.

 

ky_raptor if i am not mistaken that 426 engine has about every engine mod you could probably put on it.