On 2/25/2016 8:21 PM, Ed Pawlowski wrote:
On 2/25/2016 9:00 PM, krw wrote:



Well hopefully there is no combustion inside of the manifold and
having
said that, typically the fuel is combusted when it is under higher
than
atmospheric pressure. And engines work better when the fuel
bypasses an
intake manifold altogether and is atomized, by an injector, at the
optimum location and time inside the cylinder. BUT YES you need a
vacuum inside the manifold to draw fuel into the heads and cylinders
from a throttle body or carburetor. IIRC sometimes up to 15~30 lbs of
vacuum in the manifold at idle, considerably less during full throttle
with the butterflies fully open.

15-30lbs.?? Atmospheric pressure is only ~14psi.

Vacuum, not pressure.

Exactly the problem. You can't pull a vacuum higher than the outside
atmospheric pressure. That is, once you suck all the air out of the
room (14psi), you can't suck any more. Well, The Donald can, but...


I think he meant inches of Hg, a common measure on a vacuum gauge. 29.92
is perfect vacuum at 1 atmosphere.



Yes! Precisely, I was mistaken. Inches not PSI, although the actual
PSI is half the reading on the gauge.