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Spent about an hour flight testing the higher
(~19" Hg MAP) stagging point.
For reference, keep in mind that it worked quite
satisfactorily with it set at ~14.5" Hg. The only drawback was that it had
to be set up very carefully around the stagging point to avoid a step
in the mixture as the throttle was moved through this point.
Bottom line first: It works very well at 19",
the main advantage being that it makes setup much less critical at stagging
point. I did it while in-flight and it took about 10 - 15 min.
total. This is a much bigger deal for those running the big injectors like
Rusty.
(Other) Pros & cons:
I normally cruise at an altitude of 12,000 - 14,000
feet. Manifold pressure at economy cruise is 17 - 18" so this means the
engine is running on only the primaries now. Less wear & tear on the
injectors? Who knows / who cares? I'm still using my 17 year old
injectors that came on my original junk yard dog engine and they have yet to
cause a problem.
Biggest 'problem' was the effect on the fuel flow
instrument. I'm currently using the one I designed that gets its input
from the injector duty cycle on one of the primary injectors. (circuit
board courtesy of Ed Anderson who neatly integrated it with a mixture monitor
curcuit). It is very accurate at cruise throttle settings after
being calibrated. Only down side is that it reads roughly double the fuel
flow when running on only the primary injectors due to the doubled pulse width
when below the stagging point. This didn't matter before because idle &
taxi was the only time the engine ran in stagged mode. Since I am
now running in stagged mode at cruise, the fuel flow now reads double
the actual flow. Bummer. Maybe I'll set the stagging to just
below cruise MAP instead of 19". Or ignore it until I get the
prototype EM2 installed which will happen soon. It knows when the EC2 is
stagged and compensates for this.
Tracy
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