Engine sucking...

[Paulo Mateiro <p.mateiro.resin@xxxxxxxx>]

Hello all.

All this talk about the engine sucking from the exhaust reminded me that I
once read that you should always keep the throttle mid-open and slip the
cluth when driving through deep water. This is supposed to keep the revs
high and prevent the water from beeing sucked by the exhaust.

It's not that the engine will SUCK anything from the exhaust, but the
pressure gradient caused by a downshift or lifting the throttle can indeed
cause the water to flow INTO the engine. When you are accelerating, you have
a low pressure (exterior) and a high pressure (inside the pipe). Fluid
mechanics tells us that fluids (in this case exhaust gas can be considered a
fluid) flows from high pressures to low.

When you are driving through deep water, you will have something like a
clogged exhaust. The water will prevent gasses from flowing out, thus
creating a hig-pressure zone at the end of the exhaust. When you take the
foot of the throttle you will decrease the pressure, but the greater
pressure created by the water is still there. So you will have a
high-pressure at one end of the exhaust and a low-pressure nearer the
engine... This will in fact SUCK the water.

I believe that with a clogged cat (meow!... - sorry) things will happen
similarly.

Just my .02 worth, 

Paulo

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