Carb heat set up

[Robin8er]

Is there a reason that carb heat seems to always rely on the engine "sucking" air through the heat muff, rather than having hot air being forced in similar to how the cabin heat works?


I'm worried about my carb heat door not sealing and therefore not being effective. I feel that having hot air be forced in like the cabin heat would be more effective.

[MConner]

Originally Posted by Robin8er

Is there a reason that carb heat seems to always rely on the engine "sucking" air through the heat muff, rather than having hot air being forced in similar to how the cabin heat works?


I'm worried about my carb heat door not sealing and therefore not being effective. I feel that having hot air be forced in like the cabin heat would be more effective.

I have tussled with an ineffective carb heat on my -10. The small clamp on device did almost nothing. I plumbed the heat scat to one of my heater muffs without any forced air and it was equally unimpressive. The top of the air box where the scat attaches is open at both sides and I can only assume that is is far easier for the intake to draw air in there as opposed to pulling hot air through the scat.

My next step is to block off the open sides a small amount at the time to force the motor to draw hot air. I do not like the idea of continuously heating the air box by pushing hot air over it for the 99.9% of the time I am not using carb heat.

What is the optimum heat rise on a carb temp gauge ?

Mark
48X

[pa38112]

This is an excellent question. My carb heat was very ineffective, so two years ago I completely re-did the air intake. One of my concerns was ram-air from my Sam James air intake over-powering the low pressure air intake under the cowl. I thought about a pressurized intake for cab-heat, but steered away for a few reasons:

1. It is an un-filtered intake, so for the 99.999% of the time that I am not using carb heat I don't want the chance of un-filtered air sneaking past the filtered air.
2. I wanted the simplest operation possible so that when I need carb heat I know it is going to work. I did not want an extra door in the air path, but without one I would have ram air entering the cowl all of the time causing extra drag, and reducing the effectiveness of the pressure drop that I need for my oil cooler.
3. I found that with some good thought and a little effort I was able to fabricate a door that very effectively blocks-off the ram air from the air intake when I have carb heat selected.

Before my work I had a 15 degree carb temperature increase at altitude and speed. After the work, which included a new carb heat muff, I am seeing 80 degrees.