On a sbo which of these heads are the best. 7a or number 4 heads. Don't know what year. Thanks Larry

 

7A heads are 1972. 4 heads are 1967. Performance-wise, the 4, 5, 6, 7, and 7A heads are equivalent. 7 and 7A have hardened seats, but these are only induction hardened and thus not very deep. One good cut during a valve job and the hardening will be gone.

 

I found a earlier post in the archives which told what the cc's were on all the heads and what engine they came from. As this is for fitment on a 75 350 engine I guess the question would be which would give me a better bang for the buck. I'm seeing that the 4 heads are for a 330 engine and the 7a's are from a 350 with only 4 cc's difference. This is just a daily driver 83 h/o with a very mild streetable cam. Waiting on cutlassefi to get back with a suitable cam reccomenation. Larry

 

The published combustion chamber volumes you find online are all taken from the NHRA blueprint specs. The factory as-cast heads will always be larger and have more variability due to production tolerances. In addition, if the heads have ever been to a machine shop to be resurfaced or have a valve job, all bets are off.

4cc is a negligible difference for a street motor. If you use the FelPro blue head gaskets you'll make a much larger change in CR than the difference between these two sets of heads. Use either one. You will not be able to feel any difference. Whichever heads you use, get the 2.000/1.625 valves from the W-31 installed in them.

 

If they are in similar shape, get the #4 heads. It will give you around 9 to 1 with a clean up mill on the heads with Felpro head gaskets. Don't forget to open up the bowls with the larger valves Joe suggested.