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Old 20 Jan 2011, 12:41 (Ref:2818273)   #4
JohnD
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JohnD should be qualifying in the top 5 on the gridJohnD should be qualifying in the top 5 on the grid
Rushy,
Squeezing the hose pipe end is NOT a Venturi effect!
That places an obstruction in the flow, so that the pressure behind the obstruction rises.
A properly constructed venturi speeds the air (or water) in a way that causes the pressure in the restriction to FALL, as the fluid accelerates. If the fuel reservoir of a carburettor is at normal atmospheric pressure then the pressure difference between that and the low pressure, fast moving air in the venturi pushes fuel out of the 'jet'.

Why do you want a lower pressure in your intake? As tristan says, you want to slow the air down around the intake, so that its pressure is a high as possible, so as to aid induction.

If you are thinking of the 'trumpets' or so-called 'ram-pipes' that are fitted to the intakes of carburettors, these are more to do with:
a/ getting a smooth airflow down the intake - the rolled edge is most important, it should include 180 degrees. The slight narrowing is part of that airflow smoothing, not a venturi.
b/ using pipe lengtht to tune the standing wave that occurs in the intake to a favourable frequency to aid induction, by increasing the pressure at the valve. Shorter the pipe, the higher the revs at which this effect occurs

John
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