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I'm trying to get into upgrading my '08 SS a little this year since i've gotten used to it (had it for a year this coming July and my car before it was a '93 Buick LeSabre :giggle:). With that being said i've looked online a lot and people are saying there's a major restriction in the Downpipe and there's a noticeable difference in your car after you get it upgraded. Which is the best way to go, catless or with cat? Also what are the benefits of the two? I want the most bang for my buck as well as the best throaty muscle-car esque sound I can get with a stock exhaust (I'm going to change them out later this year.) And where is the best place to get the downpipe from? Thanks in advance!
 

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The earlier Wbodies had a nasty restriction in the downpipe known as the 'u-bend'. I'm not sure if the LS4 cars have the 'u-bend' or not, but deleting the cat (and removing the OBDII checks in the tune that looking for it) should net you a few extra horsepower and will definitely make it sound throatier.

If you don't have emissions, catless is the way to go for sound and for performance.

I'm honestly not sure if anyone makes a 3" catless downpipe for the LS4 Wbodies now - ZZP, Hogan, and Wbodystore all used to sell them, but I think the market has dried up. You may want to contact Wbodystore or ZZP and see if they can do something for you.

Good luck!
 
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The 8th gens don't have the u-bend, so I'm not sure why they are considered such a restriction.
 

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The 7th gen downpipes were also a pipe within a pipe and the flexpiece was a choking point at just over 2".

LS4s could use a full 3" exhaust upgrade if you're looking for power. ZZP does LS4 downpipes and you can use the 04+ GP cat-back minus mufflers on 06+ Impala with your own custom muffler/tip setup.
 

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I have the magnaflow exhaust and I think it is a 2.5" exhaust. It blows the exhaust fumes out really well.
 
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