these heads are a great,low cost adition to a low compression,cast crank 400 or 440. these will bring one of the .115 in the hole piston engines to a solid 9.5 to 1 to 9.7 to 1 compression ratio dependent on which headgasket used. not the most performance oriented set-up according to alot of "experts" but, they work very well waking up a smog-era motor for next to no dough.