Gas gas 400 to 450 conversion
 

If someone want.s to upgrade from 400cc to 450cc..you can buy an used or new cylinder and piston for a 450 it s working fine with the 400 crancase and the cylinder head.."plug and play"

When the FSE 400 first came to the U.S. I remember there was a kit to make them 450s.
If I remember correctly, it was just the cylinder, piston kit, and gaskets.

The Ecu also requires a remap to do it properly.