When you measured the under cowl temperature, I'll bet it was on the ground.
In this situation there is little air moving and poor cooling leaving higher
temps than one would find when flying.

When carb ice occurs, the already low temp is rapidly reduced due to lack of
power. If you do not apply carb heat quickly enough, you become a glider.

The trick is to get carb heat applied before the engine quits so you have
heat to melt the ice. You need a lot of heat and quickly,

Ray Toews wrote in message ...
Has anyone ever tried using cowling air under the engine as heated air
for carb heat.
Because of tight cowling space I am thinking of building a door in the
lower cowl for fresh ram air and then closing it and drawing air from
under the engine, cooling air coming off the cylinders which seems to
run about 120 degrees as my heated air in case of carb ice.

I have measured the under engine air on two airplanes now and it seems
to run around 120 deg. so this must be fairly typical and would seem
to be more than adequite to get rid of carb ice. I have never had the
opportunity to measure heated air coming off exhaust manifold.

I would build it so fresh ram air is unfiltered and alternate, heated,
air would be filtered. in this way I would always taxi using warm
filtered air but in normal flight use cold ram air.

Makes sense to me, but then so does capitalism.

Ray