ORIGINAL: airbusdrvr
ORIGINAL: Sport_Pilot
Manifold pressure [vacuum] decreases with demand.
I said manifold pressure, that is the opposite of vacuum, not the same thing. As manifold vacuum goes up manifold pressure goes down. A manifold vacuum of say 30'' of vacuum ( a perfect vacuum as that is as high as it will go) is a lower pressure than 10'' of vacuum. The atmospheric pressure is pushing the metering rod in because the pressure in the manifold is low. A spring is balancing these forces so that there is equal force on bothe sides of the meter diaphram. As the manifold pressure goes up the increased pressure and spring to gether push's the metering rod up causing the fuel mixture to be enriched.
I usually convert all my pressures to absolute pressure before starting calculations, that way there is less confusion.
I don't think the carb on the four-stroke OS FT-120 twin-cylinder engine is this advanced. It is just the regular two/four stroke style carb with a rotating barrel. My only reason for posting this question was my curiousity whether or not the high speed needle when set on the ground would be affected by the air pressure going toward the forward facing carb opening. Most other four-strokes have the carb at the rear of the engine facing downward. Most two strokes have the carb at the front of the engine facing upward or with a small amount of forward tilt. This carb is positioned horizontally with the venturi/opening facing directly into the airstream.
And others said that there will be little or no effect. Ram air effect is low, it is measured in inch's of H2O because it is so low. I doubt it is more than a half inch of Hg. They do this in drag racing because they are after any advantage they can, it may be worth only a few thousanths of a second and not noticebale at all, but a few thousandths of a second could be the differance of winning or losing, and its cheap so they do it.