In article
,
Frank Krygowski wrote:

The flow of air in the intake passages of an engine is caused by
pressure drop. The more restriction in a certain location, the
larger the pressure drop required across that restriction.

Air first enters the "air horn" portion of the air cleaner because
pressure within the air horn is lower than atmospheric. Yes, even in
the air horn, pressure is lower than atmospheric.

Air flows through the filter element of the air cleaner because the
pressure inside the air cleaner (downstream of the filter) is lower
than the pressure in the air horn.

This explanation continues all the way to the intake valve, where the
pressure inside the cylinder is lower than the pressure just before
the valve.

This is true even in a diesel engine. Its intake passages are below
atmospheric even though there is no venturi.

An internal combustion engine would be unable to operate if all those
things were not true. The atomized fuel/air mixture would never get
into the cylinder otherwise (slightly different in the case of fuel
injected engines, which has a different mixing point for the fuel and
air than a carbureted engine).

The only important exception is an engine which is supercharged or
turbocharged. But even there, pressure in the intake of the 'charger
is lower than atmospheric. The 'charger pumps it up in order to
increase the flow of air and fuel; but from there on, the pressure
gradient is downhill, except for the two-inch expansion of the
venturi (where fitted). In that section, flow is maintained by
inertia, not pressure drop.

So once again: Supercharging or turbocharging excepted, the entire
intake passage, going all the way upstream to the air horn, is below
atmospheric pressure. Otherwise flow would not occur.

Once again, "jim," if you restricted your posts to what you actually
know about, your posting volume would drop by over 90%.

But what fun would that be, without "jim" tossing all those ducks in the
barrel? He may be able to "do the math" but it's the fundamental
understanding that eludes him. He re-enacts the "Ballad of Irving" in
these threads every time:

http://dmdb.org/lyrics/irving.html