Todd wrote:

"Could
we use an (aircraft) carb as an air valve and add a tps onto the throttle
shaft? I don't think this would be a big engrg job. In operation you would
need to shut off the fuel to the carb or servo (using the mixture control)
while the EFI is operating the engine."

      One question though, would the venturi be susceptible to icing when
the carb
fuel is shut off ? Without this fuel atomizing in the venturi is there
still
an increased chance of ice forming due to the pressure drop in the venturi
?
     Do those of you flying with EFI have provisions for carb heat anyway?"

Todd, I understand the reason for carb ice has to do with the vaporization
(latent heat of vaporization) of the fuel dropping the temp right after the
venturi (which draws in the fuel). The lower temp causes the moisture laden
air to form ice in this area.  Thus, if your not putting in fuel, you
shouldn't have a drop in temp and no ice formation. Injected a/c engines,
don't have carb heat because they inject the fuel right at the valve port.

However, with that said,I've recently learned that the a/c injected (and
carb) engines bring the airflow thru the servo (air valve) and into an oil
sump heated area to prevent ice crystals from entering the cylinders. I
don't know if that is unique to an air cooled engine, or if you can form
ice downstream of the air filter, or is this just for cooling the oil sump.
Does anybody know?

p.s. I did have a provision for carb heat (alt air) because I was concerned
about flying thru freezing rain which can plug your air inlet.
Chuck Harbert

 
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