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Pressure vs flow 1

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Mark911

Automotive
Oct 10, 2005
10
I'm trying to understand why some say that on the same exact engine a turbocharger which has a high flow capacity at a relatively low pressure ratio actually flows more air than a supercharger at the same boost level? I understand how it can produce more power as other variables come into play. I understand that the pressure/density is generated in different manners (internal vs external compression) and this affects the volumetric and thermal efficiencies. However, everything else being equal (air temps in the manifold via intercooling, pressures, etc), how do you explain this statement?
 
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I believe Porsche still use KKK turbochargers not Garrett turbochargers? VNT is Garrets descriptive name for the variable vane turbine housing. I am guessing that KKK (and Porsche) are calling essentially the same thing a VGT.

High temperatures are blamed for causing VNT unreliability, but I am not sure exactly why. The vanes see no higher temperatures than the turbine wheel, and we never see wheel failures due to temperature. The vanes are quite likely made from a similar alloy as the turbine wheel, and are under far less mechanical stress.

To me it seems more likely that the vane actuator sliding ring mechanism just eventually blocks up with exhaust deposits and finally jams solid. That is going to be due more to what comes down the exhaust pipe rather than just temperature. The thick crust that can sometimes build up on the back of the exhaust valve on high mileage engines is the sort of thing that could likely cause the problem. It takes more than just temperature to do that.
 
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