Aluminum heads

dart_68 said

Here's a thought. If, for the purposes of this argument, that we agree that an aluminum headed engine can resist detonation better than an iron headed engine thus allowing higher cylinder pressures (after all, isn't that what we're really talking about?)- could the difference be that of the materials themselves, aluminum vs. iron, and not how fast heat can be dissipated?

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The only meaningful difference between the materials is strength and hardness. Iron is harder and stronger. Alum is softer, and weaker (lower modulus).

So, if there IS a difference between the two heads when it comes to compression performance, it would have to be from some intrinsic property of the material - deformation can account for some lost power due to greater deformation, but any decently designed alum head won't deform enough to impact performance noticeably and this would not help much with detonation (pre ignition) resistance.

If deformation isn't the difference, then it has to be down to heat. But none of the math or reality supports there being much difference in the thermal performance either.

The only place that may have an effect would be the ability for the alum head to draw heat from the exhaust valve slightly faster. I think there's better ways to deal with that than changing compression.