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Old August 28th, 2010, 18:57   #21
Moderator at Large
Join Date: Jun 1999
Location: Brampton, Ontario, Canada

Are you talking about the inlet tube for the turbo compressor?

This tube must inherently neck down to the same diameter as the turbo inlet, which is quite small. This inherently means that the absolute pressure will go down in accordance with the Bernoulli principle. Bernoulli pressure drops shouldn't be confused with frictional losses - but your simple manometer cannot tell the difference between the two. As long as the reduction in diameter is reasonably smooth and consistent, the reduction in pressure (because of the increase in velocity) will be in reasonable accordance with Bernoulli, and not greater than that because of frictional losses.

I know that for the Mk5 turbo inlet pipe, it doesn't look like one could do much to make it any better. I think the Mk4's had that "pancake" pipe going across the front of the engine to the turbo inlet. If there is a place where there is restriction in the system, that would be it. But still ... if the internal cross sectional area of that pancake is at least as much as the area of the turbo inlet itself, it probably isn't meaningful, because Bernoulli is going to dictate that the pressure is going to drop even more going into the turbo inlet anyway. I don't know how the cross sectional area of that pancake compares to the turbo inlet.
Brian P.
formerly ... 2006 Jetta TDI 5-sp, Spice Red, Unitronics stage 1, 0.681 5th gear.
and before that ... 1996 Passat TDI, Silk Blue
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