I remember reading somewhere, maybe here, maybe in one of the car mags that due to aluminum's ability to dissipate heat better than cast iron, you COULD run more compression. I don't think it said that you HAD to. I think it was said that you could run ABOUT one extra point of compression with the aluminum before you had the detonation issues that you would have had with the cast iron. And I may have misunderstood all of that and gotten it wrong.