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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 fredmeister View Post
Now you are thinking and starting to see how the whole system works!

The exhaust backpressure does add to the force slightly opening the valve. But it is negligible to the force from boost on the wastegate diaphragm. Plus it no longer has any effect once the valve cracks open breaking the seal with the valve seat and pressure equalizes on both sides of the valve head.

Let me chime in, Fred is correct, the exhaust pressure does factor in to the WG's initial valve opening. That's why if you were to bench test your WG, you'll find that (even with a brand spanking new WG) it won't open at the spring it .8 bar or whatever's in there. It usually takes a few psi more. .8 bar is just shy of 12 psi, and if I recall it took close to 16 psi to open my Tial (I bought it used, so take that into consideration). All of that is factored in when they design the proper spring tension to deliver whatever boost you're after (I got this trinket of wisdom from personal experience when I first got my Tial and decided to test in prior to installation. Freaked out, contacted Tial, and the rest is history).
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 06-04-2013, 07:15 PM
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