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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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Originally Posted by 911st View Post
Seems it would be easier to test the WG on the car by listening or feeling when the WG valve starts to open if the car is running instead of removing it and watching the valve's opening visually on a test bench.

I am far from a WG expert but if exhaust pressure were a factor then to be accurate we would probably have to test it on a dyno at full boost as pressure in the exhaust before the turbo can be 50% - 70% or more of boost pressure and probably increases with HP and or RPM.

By the WG's design, pressure is against the head of what is basically an exhaust valve but the key is that pressure it trying to make it past the valve seat. I do not think the pressure against the top the the valve actually pushes the valve in any way to change or restrict its opening pressure.

Again, I do not know for sure but I suspect the factory procedure might be more one of convenience.

I am thinking there are two things basically relevant to what boost a WG will retain. One is the spring tension, the other is the capacity of the WG vent. If it more open than Porsche expected like with out its connection fittings, it will take more pressure to open the WG. This might be why it could take more pressure on a bench to open it.
If you've ever tested a WG yourself and done a little research, you'll find that exhaust pressure does have an effect. When I bought my Tial a long time ago and tested it on the bench, I was concerned that it wasn't opening fully at the given spring tension. It was the Tial technical service people that confirmed the exhaust pressure part of the equation.
I suspect that the condition of the WG valve guide will have a lot to do with how much air pressure may be needed to open it aginst the stated spring pressure. A worn guide does allow some pressure to pass. These things aren't rocket science cutting-edge technology, unfortunately.
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 04-18-2010, 12:48 PM
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