"Bob F." wrote in message
...


"Morgans" wrote in message
...

"Bob F." wrote

Here's a question ...
When a normally aspirated engine quits while at cruise, how does the
MAP react with respect to the throttle?
Does it indicate zero?
Does it indicate barometric pressure?
Does it pin? (Go to max)?
Does it follow the Throttle (high MAP with a high throttle setting ,
low when set to low throttle setting)?

From a theoretical point of view, I vote for the last choice. Why?

I would think because, if the prop is still turning, the engine is still
an air pump, just as much so as if it were still running. The "suck"
part of the suck, squeeze, bang and blow is still there. If the
throttle is closed, the throttle butterfly is closed so the suck is
trying to pull a partial vacuum.

I would think that because the engine is turning more slowly, the
ability to pull as low of a MAP will be lessened, (higher MAP-just to
clarify) than the pressure you would normally see at the same throttle
setting with the engine running.
--
Jim in NC

Correct, at least your first paragraph. With respect, I don't understand
your second paragraph without reading into it.


The windmilling prop will turn the engine slower than it was turning under
power. 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.

--
Geoff
The Sea Hawk at Wow Way d0t Com
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