OK, here is the real question behind this with regard to my upcoming engine build of an aluminum head 383 I question using flat top verse dome pistons.

1. Is there a h.p. performance difference? I know it likely depend on different things in different engines but I am taking specifically about MY engine build with Brodex aluminum heads and a planned on TRUE 10-1 compression.

2. Would there be a difference in octane requirements between the flat tops and domed pistons? I plan to run on 91 octane pump gas hence my questions.

 

I have Brodix RaceRites and 10.5:1. Run 91 octane just fine. Never have heard a ping. I’d go 10.5. I sometimes wish I’d have stayed at 11:1 but no regrets.

 

How do you know it’s a “ true” 10:1 if you don’t know the dome or chamber sizes? What I mean is flat tops at 10:1 will need a smaller chamber in the head. 10:1 with domes will need a larger chamber. Not sure what volume is offered from Brodex.

As you know, octane requirements vary depending on a lot of factors, compression (static compression) being only one factor….

cam (and dynamic compression) can affect octane requirement as well.

chamber design ( swirl, quench, etc), dome size and design, etc, material, finish (cnc work, polished chambers, etc)

 

Heres a thought.
Conventional wisdom says more compression makes more power all else being equal.
However, newer thinking is less or no dome, smaller combustion chamber and even a dish in the piston top is superior. Compression ratio can still be adjusted as desired.

 

My 0.040" 350 was built with flattops poking 0.007" above the deck, and has a true 10.45 CR and 0.040" quench with the Cometic 0.047" head gaskets (we cc'd the Bowtie Phase 6 heads and matched each chamber volume). It runs on 91 octane. There are options other than high domes below 11:1 CR.

 

The Piston engineer at Sealed Power developed or redesigned most of the Forged Piston line they still sell today. He told me he could make more power with a dished piston every time if he could keep the compression within 1/2 point of the flat top or dome. It had to do with enhancing flame travel and a more complete burn and he could run a little more timing without detonation. So in the old small block Chevy's smaller combustion chamber cylinder heads with a dish or flat top can outperform a Domed piston with a larger chamber head. Assuming the chamber designs are of equal quality for air flow.
Detonation is different from engine type also. A 327 will inherently have less detonation than a 350 or 383 if all other parts are equal, same head design, same compression, same deck clearance. Comparing what works well in a 327 or 350 to build a 383 is not exact. You need to know what works well in a 383, the longer stroke affects things and makes it a little more prone to detonation. Even Rod length makes a difference as it changes dwell time of the piston at TDC. Lots to think about. One more thing, all flat tops are not equal, some have 2 valve reliefs and some have 4. Some are destroked by .020 and some are full deck height. For performance full deck height is preferred.
Mark

 

My understanding is that the ONLY reason to use a domed piston is to achieve a desired compression ratio that cannot be achieved with a flat-top or dished piston. The dome is a "compression crutch" that achieves higher compression in exchange for less optimal flame travel.

 

The dome piston allows for open combustion chambers which can dramatically reduce valve shrouding making more power than any other mod. In the end, the only way to get more torque from an engine at low engine speed is with more displacement or higher compression. Pick and choose the poison just about every mod has a plus and a minus.