Pontiac Gurus what heads should I use

I am rebuilding the motor in my pontiac with a 389. I have been told that putting 400 cubic inch pontiac heads on my car would decrease the compression ration and had horsepower. I was wondering if anyone knew which ones to use will the 96cc combusion chamber heads lower the compression to much or do I need to get 72cc heads

 

I'd use 6x heads should get the comp down to at least 9:1 they are still pretty easy to find and not too expensive yet.

 

Keep in mind that there are two (2) different 6x heads. Bout 20 CC different between the two.
"Pontiac Slim"

 

how do you know which one the 6X heads are are they the ones with 96cc or 72cc combustion chambers?

 

Back in the 60's Pontiac used chamber volume to control the compression ratio. So if you have the small chamber heads now, which I think are 10.75 to 1 compression ratio (that's what my 68 GTO has), then by going to the larger chamber, you will drop you compression ratio about 1.5 points, if my memory serves me correct.

If you are rebuilding the engine, did you already buy new pistons? If not, you could buy some dished pistons and use your old heads. That way you don't need to buy new heads.

The best low compression heads are the 73-75 Super Duty ones, but those are real valuable. Along with the 455 blocks they were attached to. I think the next best heads are the early 70's 400 heads. You want ones after 70 when the compression ratios dropped, so they still have the bigger valves and ports. The 60's low cpmpression heads have small valves and ports.

There are several Pontiac specific sites that can give more specific info.