Steve Hagar wrote:
>
> The carbs are
> the float bowl type as on my BMW, these puppies are vented to the
> atmosphere to work properly. How can you get away with pressurizing the
> intakes without blowing fuel out the bowl vents?
As long as you have a vacuum in the venturi relative to ambient
pressure, that won't occur. So I guess more boost = more power = more
velocity past venturi, and thus more venturi vacuum.
> These carbs being the
> constant velocity type open their throttle slide in proportion to the
> amount of intake vacuum behind them available. Why doesn't increasing the
> differential pressure around the throttle slide cause problems with this
> type of setup?
They have a conventional throttle butterfly. They call them constant
depression, where a vacuum diaphragm adjusts venturi cross-section
depending upon throttle position.
> Has anyone come up with a routine to be able to lean the
> mixture at altitude for better fuel economy?
Rotax engineers considered copying that 75-year-old technology, but
couldn't understand it. Actually: 1) above constant depression setup;
2) computer-controlled turbo fools carbs into thinking they're roughly
at sea level up thru 16,000 feet; 3) water-cooling permits leaner
overall mixture - the 912 uses basically same carbs and thus no
mixture control either.
> Finally does the turbo heat
> the incoming air enough to pull cold air from the outside without having to
> worry about the onset of carb icing?
Even at small boost levels (little compression heating), induction air
is still going past rather hot metal in the turbo assembly. Couple
builders have even installed intercoolers; Rotax installation manual
has no carb-ice caution re an intercooler (and do they ever caution
about everything!).
Regards,
Fred F.
A063, N3EU
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