450 motors

Will the YZ450f or the WR450 motor fit ina yfz 450?

I would say yes, with a few modifications.

like what mods.?

Most likely you would have to fab different motor mounts.

all of the mount or just certain ones?

depends on where the engine fits in

You would have to see how the motor fits in the frame. You would then find where the motor mounts on the motor are and then weld some tabs to mount that motor to the frame. I've seen plenty of people do it with the CRs so I don't know why the Yammies wouldn't work.

OK i have a 06 yfz450 motor that has a hole in the bottom end by the shifter shaft and i know 04-05 yfz has 11:9.1 comp and the 06-08 have 11:4.1 if i where to use a 04-05 bottom and and mate it with my 06 head and use my 06 piston would i get the 11:9.1 comp or would i have to use the 04-05 piston?

good question!! i think the bore, stroke and head are the same, i think it was a piston change.. not for sure tho. let me know what you find out its something besides the piston. just get an R6 motor if you have to modify motor mounts

i has to be something in the bottom end like the crank or piston b/c 04-05 yfz have 11:9.1 comp. with only a 439cc and the 06-08 have 11:4.1 with a 449cc. And the only thing i can think of is its either the crank or the piston