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But valves are usually stainless steel, right? The coefficient of thermal expansion for stainless steels is "nothing" compared to Aluminum. The combustion teperatures would be mostly touching the stainless steel so I think the difference between a running engine and a hot stopped engine would not be so great, as the Aluminum would still be "warm". The Aluminum would not see the swing in temperature. Valves, cams, and rockers should not expand much- most of the increase in lash would be the Aluminum cam carrier heating and expanding.
I am not sure about the thermal conductivity of stainless steel compared to Aluminum, or Titanium, for that matter. The stainless steel may hold on to the heat longer than the Aluminum.
It would be interesting to examine an engine with DFLs and ceramic/DLC coatings on the pistons, combustion chambers, and exhaust port liners (like the 964). That would block some of that heat and would be a good way to test your theory.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
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