far as i know youll just get a higher compression ratio out of it. something like the 4bbl Clevelands 10.5 - 10.7 ratio ( twas one of those, thine mind not recall them so well ) which is a bit nicer than the open chamber heads ratio. i cant quote any numbers off of it, as i really dont know anyone whose used them before. i would have bought some but they cost too much. i got my set of 4bbl closed chamber heads for less than the Aussie's going rates. screw streetability, i want power!!!!!!
There are two basic styles of Cleveland heads, open chamber and closed chamber. The open chamber heads will give around 8.5:1 compression with a flat top piston. Closed chamber heads will give about 10.5:1 compression with flat top pistons. The ratios are just approximate, and are good enough for conversation purposes. The Aussie 2V heads are closed chamber.
OK, Now we get to the 2V and 4V heads. The differences in 2V and 4V heads are very similar to the oval port and square port big block Chevy heads.
2V heads have relatively small ports. They're still much bigger than windsor ports though. 2V heads were all small valves, again relatively. 2.06/1.66 intake/exhaust. All 2V US-made heads are open chamber.
4V heads have large ports. They tend to be so oversize for the displacement that they tend to give the engine a 'soggy' bottom end. They do flow better at higher rpm ranges. Early 4V heads are closed chamber, later 4V heads are open chamber. The early 4Vs had the engine code 'M', and the open chamber 4Vs have the engine code 'Q'. Now for a sub-types of open chamber 4V head. The 70-72 4V heads had large valves (2.19/1.71) and the 73-74 4Vs had the smaller 2V valve size of 2.06/1.66.
Thanks for the info guys. I just picked up a pair on ebay and wasnt sure if there was any major difference between the two. Looks like there is a little potential for a boost with these heads. Thanks again.