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What is the diameter at the smallest point of the stock exhaust system?

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Old Sep 17, 2001 | 07:28 AM
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What is the diameter at the smallest point of the stock exhaust system?
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Old Sep 17, 2001 | 07:44 AM
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about .75 square inches... it is inside your Cat
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Old Sep 17, 2001 | 07:51 AM
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dope! What about after the cat?
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Old Sep 17, 2001 | 08:28 AM
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Default after the cat I wouldn't worry as the air travels down the exhaust it gets denser...therefore
it is hard to truly identify the "bottleneck" of the exhaust system.
stock system is 2.25" cat back I believe
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Old Sep 17, 2001 | 09:51 AM
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Then what is the reason for upgrading the exhaust system to an APR or Borla, ect.
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Old Sep 17, 2001 | 10:21 AM
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APR is 2.5, mandrel bent so that the diameter stays the same throughout the bends.
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Old Sep 17, 2001 | 12:47 PM
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more flow... you asked what the smallest point was. I had to correct your thinking first =)
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Old Sep 17, 2001 | 12:53 PM
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Default Thanks, but I am still confused. If the cat is small what does it matter if the rest of the exhaust
is 2 or 2.25 or 2.5 or even 3 inches. I just don't see how an upgraded cat back exhaust system can flow more if the backup is in the cat. Maybe I am just missing something.
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Old Sep 17, 2001 | 12:56 PM
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Default the entire exhaust length generates a back pressure.
by having a larger diameter exhaust you help reduce the back pressure. This reduction of backpressure speeds up the flow from the exhaust.

Backpressure generates more force that the engine or turbo has to overcome.

hope that helps
-Will
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Old Sep 17, 2001 | 01:43 PM
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Default Ok last question!! If the stock past the cat is 2.25, how does the Borla or any other 2.25 inch ..
system increase flow over the stock system since it is 2.25 inches. I ask all this bc I am considering a turbo upgrade in the near future, and I want to make sure that I get an exhaust system that is an improvement over stock.

Thanks for answering my volley of questions.
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