As I posted a couple of weeks ago, I am really interested in a project with making as much horsepower as I can with a smallblock but have the engine run on at most 89 octane. The question I have right now is this: which generally has a lower compression, a dished piston with a 64cc chamber, or a flattop piston with a 72cc chamber? Does one combo generally have a predisposition to produce less power than another?

Also, I think I've read that kidney shaped or heart shaped combustion chambers are some of the best designs. Can someone back that up for me?
Thanks.

I'm no pro, but I think you'll see a more efficient burn with the dished pistons and 64cc heads.

The compression you end up with will be determined by the actual dish volume. You can get practically any size of dish, or make one; it's not like you only get one choice. The thing is though, a small dish is 12cc, and you're talking about chamber sizes that are 8cc apart; on that scale, a dish is a HUGE change in compression, and chamber size is a small incremental step.

Head gasket thickness and block deck height are 2 other variables that dramatically affect the CR.

The one combo to avoid if possible, with pump gas, is a dome piston and large chambers.

Choose heads according to their flow characteistics and chamber design, not their chamber volume. Once you get the heads that fit your application, select pistons to match them; not the other way around. In stock heads, all the good ones are 64cc. In aftermarket ones, there's alot of variety available.

Keep in mind that HP is limited by upper RPM flow, which in turn is limited by cam profile. And your CR will ultimately limit the cam you can run. An over-cammed low-CR motor is a gas-guzzling dog around town, and a lackluster performer compared to a high-compression motor with an equal cam.

Asuming that you have correctly selected a brand and type of head already that will give you what you want, a 64cc chamber with 15cc dish will give you about 9.3:1 CR with a zer-decked block (VERY IMPORTANT to include block deck height in your calculations) and a .039" composition head gasket. Or, flat-tops with a typical 6cc valve relief and 72cc chambers, same deck & gasket, will give 9.4:1. Either of those with a cam in the 220-225° .050" range should give you about all you can stand with the low-grade fuel.