engine swap

[DAVE14]

Does any one know what motorcycle engine can most easily made to fit a 400 ex & no I dont mean an xr400,Ive seen a site with a 650 xr motor in a ex but there must be more serious quads out there.
I need a rebuild but still dont wanna get smoked by a 450 yet still need something rideable not a drag bike.

Any help would be great thanks.

[bwamos]

cr250 2-stroke or a ktm520 are your other options, while keeping it ridable. Both will require some frame mods for motor mounts, etc.. the 520 requires a removable upper rail so you can pull the motor without having to remove the cylinder (its a tall motor).

[YZ400EX]

YZ 400, 426, 450 or CRF 450 there is all kinds of motors that can be put into an EX frame..it depends on how much you know about doing stuff like this is what is going to hold you back from putting any motor you want in one..