Pontiac engines have made good power/torque w/the compression ratios obtainable w/flat top pistons and the 400 chamber heads, like the 6X-4. I never had my 455 on a dyno but going by my weight and quarter mile speed/ET I estimate it was right at 450 HP. 6X-4 heads w/FT pistons.
The OP lives overseas, he's stuck w/the 4X 455 heads. He can get to 450 or damn near it if he ports the heads and maximizes the CR w/the 455 4X heads and does his homework regarding quench and picks a good split pattern cam and runs 4-tube headers.
The OP's 4X 455 heads w/a 0.060" cut and FT pistons and a 0.041" quench will give him right at 9.1:1; 9.5:1 is the max I, or anyone who knows what they're talking about regarding Pontiac engines w/iron heads would recommend he use, anyway.
BTW, just because YOU cannot make 450 HP- even w/ round ports- doesn't mean it's impossible for the rest of the world, even w/iron D-ports. Because not only is it not impossible, it's common.
I'd ask what happened to the idea that you cut the block to gain compression instead of the heads, or what about the quench pad that didn't exist, or what happened to "455's don't use 4X heads"? Et cetera. But all I really need to say is: Just stick to the facts.
I don't know what you are talking about when you say closed chamber heads and 88cc, but the early pre-emissions Pontiac heads were around 72cc. If you're talking about the 400 size chamber smog heads, they're not "closed chamber" heads by any stretch of the imagination. 88cc heads on a FT 455 would put the CR too high anyway.
Last edited by cobalt327; 01-05-2013 at 02:46 PM.