New LS1 Owners - Newbie Tech - straight pipe or highflow cats?

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I want to redo my exhaust but idk if to go with the straight pipe or highflows and also if i should use a 3 inch pipe converting down to the exhaust to a 2 1/2 ....its going on a 5.3 vortec ...need some advice please! Nd thanks

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I guess it just depends on what (if any) kind of emission testing you have and whether or not you want to have the pcm tuned to ignore the rear O2s. Here it's just visual inspection so many people run gutted shells or resonators/test pipes made to look like cats. If you have to pass a sniffer test, you'll want flanges so that you can easily swap back to working cats. If that's the case it might just be easier to go with high flows so you don't have the hassle of swapping back and forth.

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What about horsepower wise? Wich are better?

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