Re: I am curious about the principle behind this > - Saab 900 Bulletin Board - Saabnet.com
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Re: I am curious about the principle behind this >
Posted by JohnB (more from JohnB) on Sun, 27 Jun 2004 05:39:09
In Reply to: I am curious about the principle behind this >, ChipJ, Sat, 26 Jun 2004 03:20:58
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Everything said is true (at least the facts are) but analysis and interpretation are, umm, open to interpretation.
The weakest link theory, or in this case the restriction in the exhaust system, is somewhere between the turbine and the stock cat outlet. I'll assume the stock header is not a flow restriction. That being said, opening the exhaust behind the cat should only improve flow, assuming the stock exhaust further restricts the flow after the cat.
Flow velocity is solely a function of cross sectional area, pipe friction, and pressure differential. Opening the catback to 3" increases the pressure differential across the system from the cat to the catback and all things being equal, flow velocity should increase.
In every turbo application I've come across from 3.8 buicks to current saabs and volvos, generally the payoff from eliminating turbocharger restriction results in increased pressure ratio and faster spoolup. The best solution remains an open turbo pipe directly from the turbo to atmosphere.
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