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<B>IS JOE </B>
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To understand the exhaust system on the car:
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The car is a 6 cylinder, so it has 6 exhaust ports. So coming off of the engine, you first have a header, which takes the 6 and combines it down to 2. (Its actually 2 banks of 3-to-1). There are 2 catalytic converters in the header.
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Next, you have the y-pipe, which combines the 2 outputs from the header into a single output, hence the name "Y" pipe. At the end of y-pipe is the third and final catalytic converter. If you look under your car, the y-pipe starts right behind the front wheel and goes to a little past the mid way point of the car.
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After the y-pipe, you have the b-pipe. Its a simple pipe with a resonator to help control noise.
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Finally after the b-pipe, you have the exhaust or the muffler leading out to the back of your car.

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So like any exhaust system mod, the goal is to remove restriction and improve flow. Some people replace the header with a less restrictive one. This also removes the 2 catalytic converters which are a big restriction in the exhaust system. Similarly with a y-pipe, you can replace it with one that does not have a cat. That will also remove some restriction. The b-pipe simply only has a resonator, so switching that out for a straight pipe may help a tiny bit with the flow, but you'll be getting mostly sound. Note: a cat-back exhaust replaces both the muffler section as well as the b-pipe, where as an axel-back exhaust only replaces the muffler section.
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You should also note that there are many different kinds of y-pipes, and headers out there. Some optimize flow for lower gas velocity, giving you low end torque, while some optimize the exhaust system for high gas velocity, giving you top end, high RPM horsepower. If you do a search in the Go Fast forum you should find a ton of info about this.
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Hope that helps

<B>Special Thanks to IS JOE for the nice simple and to the point explaniation</B>
 
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