will a 400ex motor fit on a 300 ex frame without a lot of mod?

 

I would look this up. I know a lot of people would say just to leave the 400 motor in the 400 frame since it is built for the suspension and stuff. However if you had the two separate, and wanted a project why not. Im sure if you had an idea what you were doing, you could make it fit.

 

where would you find that answer? will the top end of a 400 ex fit a 300 ex bottom end?

 

i think your brother in laws 350 warrior beat you at the dunes

 

400 top wont fit 300 bottom

 

A 350X conversion would be cheaper and a much easier swap not to mention a more well ballanced quad.
A BIG problem with the 400EX engine swap into a 300EX is the swingarm pivot location in relation to the 400EX countershaft after you modified the frame for the engine to fit. It's too far off to ever work properly in the rear suspension department. Many have tried it and it's not worth it.
And on the 350X conversion, the 350 engine is actually capable of MORE power than a 400 is. A 350X can be modified to 60+HP if your pocketbook can support it. Just upgrade the chassis and suspension as you go.
You will never get that out of a naturally aspirated 400 engine.

 

they sell the 350x conversion brackets at powroll for like 100 bucks, that way it just bolts right in no modifications to the frame are necessary in case you ever decide to switch back