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Old 09-04-2002, 12:25 AM   #11
Scooby Newbie
Member#: 5094
Join Date: Mar 2001
Location: Gaithersburg, MD, usa
11.96, 1.64, 115mph!

Default The reason for the 4" pipe

I think many have lost sight of the reasoning behind using a 4" DP.

1. Reduce boost creep due to restricted flow out of the wastegate.

2. Streatching a 3" pipe to fit the entire outlet of the turbo makes the exhaust piping thin, causing reliability issues.

3. Smooth flow between the exhaust and the wastegate gasses before they enter the cat.

4. Smooth taper to prevent joining the gasses too quickly, causing turbulence and resulting in poor performance.

5. Any backpressure behind the turbo is too much backpressure.

Many choose not to use a 4" pipe due to the extreme cost in mandrel bending one.

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