2.5in vs 3in exhaust - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Coop[580 · 03-22-2018, 06:55 AM

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.

robrocketanski · 03-22-2018, 07:06 AM

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.

Coop[580 · 03-22-2018, 07:41 AM

If it helps it’s a stainless works system. And I have kooks headers and off road kooks cats.

d454brisson · 03-23-2018, 10:10 PM

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.

AJensen383 · 03-29-2018, 12:00 PM

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"

ExhaustFreak · 05-24-2018, 04:27 PM

The Cuthroat exhaust might give you the the flow you want. No need to straight pipe. Plus it's reversible. https://youtu.be/3Ch4hCTPTZw

BlaqWhole · 05-24-2018, 04:44 PM

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.

03-22-2018, 06:55 AM	#1
Coop[580 Drives: 2012 ZL1 Ashen Grey Join Date: Apr 2017 Location: NW Indiana Posts: 378	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. __________________ 2012 M6 Kooks 1 7/8, off road pipes , full corsa exhaust ID1300s/ 22% lower / 2.5 upper, JLT CAI, DSX flex fuel, DSX AUX fuel pump. S19 cam Tuned and built by Speed Inc 635/632-93 octane 725/738-E85

03-22-2018, 07:06 AM	#2
robrocketanski Drives: ZL1 Convertible Auto Join Date: Apr 2015 Location: Macomb, Michigan Posts: 330	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. __________________ LS3 intake and throttle body, Huron Speed Products twin turbo with 6265 oil less turbos, and 3" header back, JRE smooth cam, ID1300, Fore dual 450lph pumps with MSD voltage booster, A6, 305/45/17 MT Street R

03-22-2018, 07:41 AM	#3
Coop[580 Drives: 2012 ZL1 Ashen Grey Join Date: Apr 2017 Location: NW Indiana Posts: 378	If it helps it’s a stainless works system. And I have kooks headers and off road kooks cats. __________________ 2012 M6 Kooks 1 7/8, off road pipes , full corsa exhaust ID1300s/ 22% lower / 2.5 upper, JLT CAI, DSX flex fuel, DSX AUX fuel pump. S19 cam Tuned and built by Speed Inc 635/632-93 octane 725/738-E85

03-29-2018, 12:00 PM	#5
AJensen383 Drives: 2014-ZL1-M6-CRT, 68 camaro SS 496 Join Date: Feb 2012 Location: N.E. Pennsylvania Posts: 262	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" __________________ 2014- Crystal Red-ZL1 #1601, M6, Recaro, sunroof, Nav-stock-SOLD 1968 Camaro SS Clone- 496 BBC, Legend 5speed, 12 bolt 1970 Nova SS- 383 SBC 588hp, 200-4r, 12 bolt

03-23-2018, 10:10 PM	#4
d454brisson Drives: 2014 ZL1 Join Date: Jul 2016 Location: Baltimore MD Posts: 345	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.

05-24-2018, 04:27 PM	#6
ExhaustFreak Drives: Lexus GX 470 Join Date: Feb 2015 Location: Indio,ca Posts: 16	The Cuthroat exhaust might give you the the flow you want. No need to straight pipe. Plus it's reversible. https://youtu.be/3Ch4hCTPTZw

05-24-2018, 04:44 PM	#7
BlaqWhole Account Suspended Drives: 2017 Camaro ZL1 A10 Join Date: May 2012 Location: NJ Posts: 7,692	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.