Kyle Boatright wrote:

"Dave Hyde" wrote in message
...

Ray Toews wrote...

Has anyone ever tried using cowling air under the engine as heated air
for carb heat.

Serveral RV-builders including me have tried something similar.
Van's sells a mini heat muff that doesn't do mucgh but serve as
a mount for scat tube, so in essence we're drawing undercowl
air into the airbox when carb heat is selected. Sam Buchanan
has a picture on his website:

http://home.hiwaay.net/~sbuc/journal/engine4.html

about 1/2 way down the page. I did the same thing on an
RV-4 and I get a barely perceptible RPM rise when I select
carb heat, which tells me it's not helping much.

Your call.

Dave 'hot air specialist' Hyde



You get an RPM increase??? Sumpthin' is way, way wrong with that... ;-)

With the exact same setup, I get a barely perceptible RPM decrease...

I thought the same at first, but he may be referring to turning on the
carb heat after he's already accumulated enough carb ice to noticeably
decrease his RPM. In that case, applying the carb heat should increase
the RPM as the ice is removed.

Matt