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Old 03-22-2018, 06:55 AM   #1
Coop[580
 
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Drives: 2012 ZL1 Ashen Grey
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2.5in vs 3in exhaust

So I have an opportunity to purchase a 2.5in catback at a decent price. What’s everyone’s opinion in the difference from 2.5 to 3in. Should I spend the extra for 3in. I know obviously more air flow, which is always needed, but will there be much of a difference in the two. But the time I’m done with the car I’d like to have around 650-700hp.
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Old 03-22-2018, 07:06 AM   #2
robrocketanski
 
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I did 3 inch and asked my tuner about it later. He said the difference between 2.5 and 3 wouldn't be much or any but the muffler makes a difference. A restrictive (quiet) muffler would lower hp compared to less muffler or straight through.
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Old 03-22-2018, 07:41 AM   #3
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If it helps it’s a stainless works system. And I have kooks headers and off road kooks cats.
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605/579-93 octane
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Old 03-23-2018, 10:10 PM   #4
d454brisson
 
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Spend the money elsewhere. The factory back with no cats is perfect. Cats are still limiting you and a cat back wont help with scavenging or any other reduction for that matter.

Unless its free your money is better spent on a Cam, better tune, more pulley etc.
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Old 03-29-2018, 12:00 PM   #5
AJensen383
 
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From everything I have read, a 2.5" system should be plenty..There seems to be lots of guys between700 -800WHP still using the stock 2.5" NPP ...Is the stainless works system for an SS since its 2.5" , all the aftermarket ZL1 cat backs I have seen are 3"
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Old 05-24-2018, 04:27 PM   #6
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The Cuthroat exhaust might give you the the flow you want. No need to straight pipe. Plus it's reversible. https://youtu.be/3Ch4hCTPTZw
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Old 05-24-2018, 04:44 PM   #7
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If I remember this correctly, a few years ago Bo White swapped out a 2.5 inch for a 3 inch OBX catback on his supercharged Camaro and the difference was about 50 HP. That is, if I remember correctly. I know it was a significant number. I always say go 3 inch. Why not? If money is an issue, then do what is best for you. But if it is more of a choice, then go with 3 inch.
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