Aluminum heads
I believe he speaks for the metal itself. Not the cooling system or the cooling passages within the head. If the iron head can cool as well as the aluminum head, then the compression ratios can be the same same fuel. But this is not the case.
This just isn't true Rob. Think about it. The time it takes for detonation to occur happens so fast that the metallic structure of the head has zero influence on it.
Somewhere on here I typed out several AJ length posts explaining the cooling system and how it affects CR much more than aluminum or cast iron heads. I had to type so much my hands swelled up and I couldn't type anymore.
If anyone knows where that is, move it up and I'll finish it.
The rate of change of temperature from cruise temp to detonation temp is so fast that there is no metal I know of that can affect detonation.
That's why I harp on the cooling system so much. Slow turning, low flow water pumps, junky assed electric fans, cramped shrouds and more make it nearly impossible to control detonation rather than head material.
I could actually run a 160 thermostat and my cooling system would keep the engine at 160 even on a 100 degree day. If I take the Thermostat out, I doubt I could get 130 degrees into the engine on a 100 degree day.
That's one reason I'm running 11:1 on iron heads on pump gas with full timing. Coolant temp control and flow are WAY more critical than an aluminum head is.
