I have a 355 sbc with 10.5 flat tops. It previously detonated when I ran some old steel 64cc turbo Chevy heads, #340292. We replaced them with a set of 68cc AFR alum heads with 180 runners and the detonation went away. I don't know if it was more from the larger chambers or the alum head material, but I suspect it was more from the aluminum since it dissipates heat better. It's may be easier and cheaper to swap heads than pistons. JMO Mep
let me rephrase...mine was 11 to 1 on paper, I never measured anything and did the math. It was a flat top piston 406 with 5.7 rods and it had a small hyd cam .507 lift dur @ .050 was about 244 I think. It had a set of the original sportsman cast iron heads with 64 cc chambers( advertised I didn't measure them)