[Rick Parker]

I think the general concensous is that near 11:1 will work with aluminum heads and a cam with enough duration that it will bleed off some of the dynamic cylinder pressure. However that doesn't allow much margin for error IE: bad fuel load, timing error, etc. Iron heads by nature do not disipate heat as quickly and therefore are a liitle more sensitive to compression ratios at this level and will require fuel with a higher octane rating to avoid destructive detonation and pinging. With iron heads the generally accepted maximum is between 10:1 and 10.5:1. This is with the technology currently available to the hobbyist and does not take into consideration the electronics, knock sensors, and various types of fuel injection used by OEMs. Refer to your engine builder as he is the one you want to listen to.