MAP behavior question

Capt. Geoffrey Thorpe wrote:
As a result the rate at which air is pumped out of the
intake manifold is reduced, which allows the air flow through the
throttle body to fill the manifold up to a somewhat higher pressure.

Careful.. there is very little "filling" going on. Unless you are in a
Mooney, at wide open throttle, with the ram air door open.

Manifold pressure is almost solely the effect of the engine sucking air
in by piston action past the air filter, and ram air difference is
negligible in the typical trainer.

Respectfully, you guys are trying to measure something with a micrometer
(ram air contribution), that was cut with an axe (throttle) (to quote
Jim Weir)..

I think some of the best reading on MP was in John Deakin's series of
articles on Fire Breathing Turbos. The first two I think were dedicated
to fundamentals...with and without turbo charging.

Anyone interested, go to www.avweb.com and search for his material.
Dave

"Dave S" wrote in message
...
Capt. Geoffrey Thorpe wrote:
As a result the rate at which air is pumped out of the
intake manifold is reduced, which allows the air flow through the
throttle body to fill the manifold up to a somewhat higher pressure.

Careful.. there is very little "filling" going on. Unless you are in a
Mooney, at wide open throttle, with the ram air door open.

Of course there is filling. Where do you think the air that mixes with
gasoline in the engine comes from? Open the throttle wide, lots comes in,
manifold pressure goes up. Close the throttle, and only a little comes in,
manifold pressure goes down (manifold "emptying").


Manifold pressure is almost solely the effect of the engine sucking air
in by piston action past the air filter, and ram air difference is
negligible in the typical trainer.

Ram air and filter pressure drops are pretty small compared to the pressure
drop across the throttle body except at wide open throttle. It's the
throttle that pretty much controls manifold pressure at any given engine
speed. (ignoring boost from turbo's, and effects of altitude for the
moment).


Respectfully, you guys are trying to measure something with a micrometer
(ram air contribution), that was cut with an axe (throttle) (to quote Jim
Weir)..


Who said anything about ram air?

--
Geoff
The Sea Hawk at Wow Way d0t Com
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