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

        The air downstream of the venturi expands and
consequently the air temp will drop. Any moisture in the air
could freeze, then carb ice, fuel or no fuel. Virg. Comments ?
 

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