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Old 09-22-2008   #4
Shane@DBPerformance
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Join Date: Oct 2003
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Re: Can't hold boost, did a boost leak test, check inside.

Backpressure might just be blowing the flapper open. To run and hold high boost on external wastegate cars, you often have to use the top port on the external and push boost to it, to act as a much stronger spring under boost. You can't do that on a single port internal gate, and internal gates often have weak springs. At 30psi intake side, you might have 50-60+psi of backpressure in the exhaust manifold/turbine housing, just pushing the flapper open all the way.
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