Originally Posted by smoulding

The 400 may not be the best choice for a propane engine. It was produced solely as a low compression engine for the '70s era polution control emissions. Putting flat top pistons and shaving the heads down about 20 mils will give you in the high 9's to 10:1 compession, if my calculations are correct. Any more shaving than that and you will run into fit problems with the intake manifold.