Cat back exhaust: how does this mod work?
Thread Starter
Safety Car
Joined: Sep 2002
Posts: 4,030
Likes: 6
From: Maryland
Cat back vs. straight pipes?
I am thinking now of putting straight pipe in place of my mufflers, to gain some hp since I have stock headers/exhaust w/ my heads/cam package.
I should mention this is on an LT1.
Question: How does a cat back system (Power effects, Corsa, etc...) really work? Is the back pressure change due to mostly free flowing mufflers or is it the resonator too ? Pipe size on the PE is 2.75", which is stock, so I'm thinking that's not it.
[Modified by sothpaw2, 7:02 PM 8/14/2003]
I should mention this is on an LT1.
Question: How does a cat back system (Power effects, Corsa, etc...) really work? Is the back pressure change due to mostly free flowing mufflers or is it the resonator too ? Pipe size on the PE is 2.75", which is stock, so I'm thinking that's not it.
[Modified by sothpaw2, 7:02 PM 8/14/2003]
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Re: Cat back vs. straight pipes? (sothpaw2)
first, on modern engines, a too great a loss of backpressure will = a loss of power.
the cat back systems do a better job of tuning the exhaust flow and removing excess restriction, without going below that threshold of backpressure, causing performance loss.
oh, there is one other point... if you are putting out a TON of power, you need flow.... plain and simple. But the mods you have don't are there yet.
[Modified by bogus, 3:24 PM 8/14/2003]
the cat back systems do a better job of tuning the exhaust flow and removing excess restriction, without going below that threshold of backpressure, causing performance loss.
oh, there is one other point... if you are putting out a TON of power, you need flow.... plain and simple. But the mods you have don't are there yet.
[Modified by bogus, 3:24 PM 8/14/2003]
Team Owner
Joined: Sep 2001
Posts: 62,141
Likes: 1,729
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: Cat back vs. straight pipes? (sothpaw2)
you will gain hp by going from a stock catback to elims, but it will be louder since youve now modded the engine, maybe too loud
It would also raise the rpm of the peak hp a little too.
The aftermarket catbacks usually use a larger diameter pipe and better flowing mufflers to increase flow, which is directly related to HP.
the gains of hp with the stock engine and most of the aftermarket exhausts is about 10hp, although maybe a little more with the engine now modded, and a couple more for just straight pipes
[Modified by vader86, 4:32 PM 8/14/2003]
It would also raise the rpm of the peak hp a little too.
The aftermarket catbacks usually use a larger diameter pipe and better flowing mufflers to increase flow, which is directly related to HP.
the gains of hp with the stock engine and most of the aftermarket exhausts is about 10hp, although maybe a little more with the engine now modded, and a couple more for just straight pipes
[Modified by vader86, 4:32 PM 8/14/2003]
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Cat back vs. straight pipes? (sothpaw2)
What cam do you have?
Here's the deal, if you have any kind of cam whatsoever and certainly with ported heads you can benefit by a better flowing exhaust. HOWEVER, the restriction might not be in just your mufflers, it's probably more in the manifolds.
Let me give you an example
My car, LT1, stock - 269 RWHP.
LT4 Hot Cam, rockers, electric water pump - 313 RWHP
hooker long tube headers, x-pipe, flowmasters - 336 RWHP
So the moral? By simply changing exhaust I picked up 23 rear wheel horsepower and 32 pounds of torque. That was with an aftermarket cam on STOCK heads. If you've got ported heads already AND a cam you are loosing something to your stock exhaust. The problem though is that you probably won't see much of a gain by replacing just the mufflers or the cat-back. Your big restriction right now the manifolds and cats.
Here's the deal, if you have any kind of cam whatsoever and certainly with ported heads you can benefit by a better flowing exhaust. HOWEVER, the restriction might not be in just your mufflers, it's probably more in the manifolds.
Let me give you an example
My car, LT1, stock - 269 RWHP.
LT4 Hot Cam, rockers, electric water pump - 313 RWHP
hooker long tube headers, x-pipe, flowmasters - 336 RWHP
So the moral? By simply changing exhaust I picked up 23 rear wheel horsepower and 32 pounds of torque. That was with an aftermarket cam on STOCK heads. If you've got ported heads already AND a cam you are loosing something to your stock exhaust. The problem though is that you probably won't see much of a gain by replacing just the mufflers or the cat-back. Your big restriction right now the manifolds and cats.
Thread Starter
Safety Car
Joined: Sep 2002
Posts: 4,030
Likes: 6
From: Maryland
Re: Cat back vs. straight pipes? (Nathan Plemons)
Nathan,
Yeah, I know, headers and cats. Your experience is great because of the numbers, I've been to your page more than once and studied the curves.
They test for emmissions here, though, so no cats is no good. The random bullet cats are $351 ea from them, and the distributers charge $270 ea for the stock size replacements. So, I figure around $1400-1500 in parts to do headers and cats.
I already had blown my budget doing the heads and cam, so I left the rest out. Most people seem to do this in stages.
Anyway, just replacing the mufflers w/straight pipe is dirt cheap.
Bottom line: It sounds like the straight pipe would be just as good in terms of performance as the $1200 P.effects cat back? That is what I am thinking, that the primary restriction is the mufflers
Yeah, I know, headers and cats. Your experience is great because of the numbers, I've been to your page more than once and studied the curves.
They test for emmissions here, though, so no cats is no good. The random bullet cats are $351 ea from them, and the distributers charge $270 ea for the stock size replacements. So, I figure around $1400-1500 in parts to do headers and cats.
I already had blown my budget doing the heads and cam, so I left the rest out. Most people seem to do this in stages.
Anyway, just replacing the mufflers w/straight pipe is dirt cheap.
Bottom line: It sounds like the straight pipe would be just as good in terms of performance as the $1200 P.effects cat back? That is what I am thinking, that the primary restriction is the mufflers
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Cat back vs. straight pipes? (sothpaw2)
Bottom line: It sounds like the straight pipe would be just as good in terms of performance as the $1200 P.effects cat back? That is what I am thinking, that the primary restriction is the mufflers
Running no mufflers with cats really is a very good sound, I've always liked it. You might consider some shorty headers sometime, they certainly can't hurt.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski