Do not discount the effect that high IAT has on narrowing the detonation
margin.  That seems like a step backwards from intercoolers

Walter,

 

We are specifically talking about normally aspirated IO 320/360 Lancairs with a forward mounted throttle body.  Maybe there is a 100F air temperature rise ( BTW, a loss of only about 10% power).  Those that have carbureted engines (O 320/360) and turn on carb heat see a much greater rise in inlet air temp since the air is heated by the exhaust pipe. 

 

What is the large margin that has been reduced a little?  How is it related to Compression Ratio?  We need facts, not generalizations.