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Discussion Starter #1
So I crawled under my '02 LB7 today and there is no cat there. But it is the 3.5 inch pipe all the way from the turbo back. So I guess my question is this, If I just have a new muffler installed would that move enough exhaust to make a difference or would the extra half of an inch from a 4 inch turbo back exhaust make THAT much more of a difference?
 

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bigger pipe allows more air flow,so it will drop your exhaust temps, and your turbo will spool faster. I just installed a 4" downpipe with 5" straight pipe and it opened it up quite a bit. And even with no kitty and no muffler it is still quiet. All I hear is my turbo.
 

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i ran a straight exhaust on my truck using the stock exhaust and it did a great job unless you add more then 120hp extra it won't really gain you anything to do a bigger exhaust or unless you want the look and sound of a bigger pipe.:cool ..i now have a 5" T/B exhaust,i just had to have a bigger pipe,plus i love the sound:D :rockin
 

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If memory serves me, every inch in diameter doubles the amount of air the pipe can flow. So, yes, going from 3.5 to 4" can really make a difference. Also, most aftermarket mufflers are 4". I would do a turbo back 4" and its up to you if you install the muffler. The muffler won't really affect flow much, its all about the sound you want. Personally, I think straight piped LB7's sound sweet!
 

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Discussion Starter #6
Thanks for the advice fellas. I've been a member of a few forums but this is the best one by far. Quick answers and honest answers. Love it.
 
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