Great data.  The induction air is taken from this hot air after it has gone
over the cylinders?  ???  I must be misunderstanding that.
 
  A look at the higher induction air effects on detonation margin would
suggest
that you would prefer to use the cooler air.
 
  Nothing like having some real data.

Walter,

 

In a fuel injected, front mounted throttle body engine an alternate air system (alternate to straight ram air) was devised that would draw filtered air from the lower cowl whilst shutting off the ram - useful during taxi and, perhaps, during the first few thousand feet AGL of takeoff and landing - thus eliminating the ingestion of "dirty" air.

 

Negative comments on such a system claimed, among other things, that such air was too hot - hotter, even, than carb heat air.

 

I contend that is false.

 

I measured lower cowl air (in my airplane only) at its hottest place accumulating all of the heat created, not at the cooler front engine area where the filter draws its air and I found that, generally, the air entering the induction system was at its worst about 100F above the ambient.

 

I measured the air exiting from the heat muff, a source of carb heat air, and found it hotter and sometimes un-measurable with the temp probe display I had available because it was limited to 99C (210F).

 

Carb air temp probes are useful in that they measure the temperature of the Fuel/Air mixture and, as such, point out that the combustible mixture is cool enough even after HOT carb heat air is added.

 

It seems that filtered under cowl air would be usable in an injected environment after raising the initial induction air by 100F, passing it thru the oil sump (just like many carb engines) and finally cooling it down by the F/A atomization at the cylinder head.

 

If used early in the takeoff phase, the engine will suffer a power loss on the order of 5% to 10% because of the rise in temp (not the total temperature of the air).   This is significant in a commercially built under powered airplane...  It is less significant in something like a Glasair or Lancair because there is an abundance of power available.  Of course, rational pilots using such a system would understand that performance is negatively affected and could choose to use the ram air in questionable circumstances.

 

I don't need anything but the seat of my pants to know that colder, denser air (more than ISO standard) yields even better engine performance/power - I do fly in the winter and additionally reap the benefits of bug-free laminar flow.