Sorry for the long intro before I get to the question, but you need to know the whole picture.

I got a crazy sweet deal on a 406 sbc for my '88 Firebird, and I set it up for raw street torque. Most guys go for top-end power, but as a true every-day daily driver, I want street manners and some measure of fuel economy along with the power.

Fairly mild cam (Comp Xtreme Engergy, 212/218 @ 0.50"). 454 big-block TBI. Holley TBI manifold. Small headers (1-1/2" primaries, 2-1/2" collectors). I get lots of flak from guys about the headers being too small, but I want the torque shifted down in the power band, not up like most guys want. Besides, I already had these headers on the original 305, and my budget is tight.

Best guess at my power output is between 420 and 450 ft-lbs, about 380 horses, with present heads. That's based on a similar build from (dare I say?) Hot Rod. My highly accurate seat-of-the-pants dyno supports those numbers. I decided on a 5500 red-line. Best shift point turns out to be about 5000. Suffice it to say, I can light'em up at will, and can "get rubber" in all five gears, even with a 3.08 posi rear. Yeah, I know... Lower gears, lower ET. But remember-- Street. Fuel economy. I only go to the strip for Test 'n' Tune. It runs in the 12's (when I can get hooked). That's faster than 99% of what's on the street, and it gets 23 mpg commuting.

Anyway, more background.

When I got this 406, it was freshly rebuilt, but to OEM specs. That means it has factory-style dish-top pistons, 33 cc volume (not "D"-cup style). Also in the interest of budget at the time, I decided to use the heads off of the old 305. I had already ported and polished them, flow-benched them, 1.84/1.50 Ferrea valves, the whole bit. They flow 192 cfm on the intakes. That's not a lot by normal standards. But a 406 at 5500 rpm and 80% VE only draws 128 cfm per port. So I'm still good there. (Am I?) With 58cc chambers, I used 0.061" head gaskets to achieve 9.3:1 compression.

Still, I'd like to upgrade the heads. Something with 200cc ports, bigger valves, higher compression. I'd love to break the 500 mark for torque. (And probably the T5 tranny along with it!)

Finally, the questions--
Typical builds in CarCraft use flat-top pistons. Never dished tops. Since the motor was fresh (no oil burn, and serious torque), and my budget is tight, I was (and still am) reluctant to replace the pistons.
-- Is there any benefit to be had from the new kidney/heart shaped combustion chambers with dish-top pistons?
-- Can I push compression up a full number (around 10.3:1) with the new heads?
-- If I get aluminum heads?  

If you go to a better flowing head you will need to open up those headers.More air in more ozone killer out.Most of the pref heads for sbc chevy run about 60cc.chamber volume,so figure a loss of 2 tenths of a point providing your presant comp ratio figures are accurate.Heart/kidney shape chambers tend to improve turbulence in the chamber for better flame front propagation and better/cleaner burn.If you want to up your compression ratio with your exsisting pistons you will need a smaller chamber head/thinner head gasket combo.All things considered.If you just put a better breathig head on it the way it is, you will see an improvement in performance due to better flow characteristics from the bigger ports and valves.With yor 305 heads I think you are leaving Horse power on the table anyway.Hope this helps you,Good luck.  

actually,ive thought about building this type of combo.with your dished pistons,think about trying out the new bowtie vortec (large port).215cc intake port,flows 258 cfm at .500 lift,65cc combustion chamber.unfortunately,the compression will be approx.9.8-10.2:1,too much for that small cam.another thing is that you will have to use a dedicated intake for the vortecs.15/8" headers are a must to let that baby breathe.just thought id  share this with ya...  

Actually, the compression won't go as high as you say. My present build is 9.3:1 compression with 58cc chambers. Just had to order 0.061" head gaskets. So 65cc chambers is no problem. You just can't use the head gaskets from a normal pre-assembled parts kit, is all.

I've given some serious thought to Vortec heads, but I already have over 200 bucks in a manifold. Won't save that much on heads that way, if I have to get the Vortec TBI manifold, too.  

Yeah, I've done some more research and found some math at http://www.malcams.com/legacy/misc/headflow.htm. The numbers say I need about 240 cfm flow to support what I'm after, with my red-line at only 5300 rpm.

I was mostly asking about quench, I guess, 'cuz with dish-tops, quench kinda goes out the window. But the improved chambers are supposed to make more turbulence even without quench area, from what I've been reading lately.

I also see very clearly that tne 305 heads are great for torque, but explains why the power drops off at 4500. Again, the math from that site above.  

my calculations were a result if you used felpro 1094(i think) gasket that has .039" compressed thickness.tight quench with dished pistons is a must,not just with small combustion chambers to make good power.tighter quench also thwarts off detonation by causing mixture turbulence in the chamber.older Nascar Busch Series engines were 9:1 mandated compresion,they used dished pistons with small chambers on 18 degree heads,they produced unrestricted 650 hp,so the combination of dished pistons and small chambers does work.