And I kind of thinking that we need another test.
We need a test of a GD 2.5" catback with 2.5" Dump tubes with the Wastegate going to open air. GD 3" catback with 3" down pipe going into exhaust. GD 3" catback with 3" going to open air.
My gut feeling is that on a car smaller than 600 turbo 5bolt will not see a gain versus 3" and that 2.5" catback with open wastegate would produce the best power curve.
Now this theory is based on Corky Bells concept that exhaust pipe being only 10% larger than turbo exhaust outlet to help maintain a exhaust velocity of 250ft/sec. I been playing with this issue is because I made a mistake making my exhaust. I started at 2.5" and then expanded to 3" but kind forgat that my turbos have a 3" outlet and my wastegates are open air vented. Bottom line I think GD results are because the wastegates keep fubar'ing the turbine exhaust flow. But then again I could be wrong and so can Corky his book is a bit dated. Now that GD has an inhouse dyno he do these 3 tests :-P
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