How much louder with gutted cats?
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From: Texarkana, Tx
How much louder with gutted cats? Just wondering how much louder the car would be with the cats gutted and the stock exhaust? I got the cutout on yesterday, and was about to get the cats gutted, but decided not to. With the cutout closed, how much louder will it be? Very noticable? I'm holding off on an exhaust system for a while. The neighbors hate me as it is, and leaving the house at 6am I don't really want to **** too many more off than I have to..
not too much louder, but the sound wont be as refined. the stock muffler will keep your volume down quite a bit, even with hollow cats, but it wont sound as good. so, even though you're waiting on an exhaust for a while, i wouldnt do it. it sounds like ****.
No cats on a Borla/Loudmouth setup will also sound like ***! I dynoed gutted cats (with stock manifolds) on my old 2000 WS6.
476 rwhp with stock manifolds, cats, cutout (150 shot).
476 rwhp with stock manifolds, gutted cats, cutout (150 shot, same bottle pressure).
Needless to say, I was shocked, disappointed and swapped my y-pipe to another racer who didn't mind the crappy sound of the gutted cats. In my case, there were no gains! Dyno verified.
476 rwhp with stock manifolds, cats, cutout (150 shot).
476 rwhp with stock manifolds, gutted cats, cutout (150 shot, same bottle pressure).
Needless to say, I was shocked, disappointed and swapped my y-pipe to another racer who didn't mind the crappy sound of the gutted cats. In my case, there were no gains! Dyno verified.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
i run Kooks/Kooks Ory w/stock catback, and it sounds pretty good, still very quiet tho. some rasp here and there, but nothing i can't live with. just get headers/ory instead of guttin the cats, give in to the urge for exhaust mods 
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Thread Starter
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From: Texarkana, Tx
I told myself I'd leave this one alone until I get the '69 on the road. I'm trying to hold out. I figure since I'd not be adding anything new really, I wouldn't be breaking my rules.
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11 Second Club
Joined: Feb 2005
Posts: 176
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From: Alton IL
My main concern is for the time being, im about to be tuned for a 200shot(If fuel holds up) Since im running stock cats, i fear of melting them and getting clogged. I still have the stock Y pipe but after that it goes into the Borla muffler to the loudmouth exhaust.
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
Gutted stock cats sound very different from an ORY. I really loved the sound of gutted stock cats with a Flowmaster catback I had many years ago on my WS6 (no rasp at all, very nice tone and slight volume increase). On the other hand, when I went to an ORY using the exact same catback, it rasped like hell and sounded horribile. Just my experiance.....
Joined: Nov 2001
Posts: 34,646
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From: Schiller Park, ILL Member: #317
Originally Posted by ls1fbod
raspy as ****, so dont get it
Maybe what you are calling "rasp" is actually something different.
I run gutted cats through a SLP Y (stocker type) and
SLP CME setup. I think it sounds pretty good. It does
have a little bit of boom to it at 2500RPM or so. I have
no rasp, I like to think because I dressed down all of
the sharp edges in the cat necks with a carbide burr
before installing. I flow-tested (ghetto style, leaf-blower
and vinyl-tubing manometer) the gutted cats vs offroad
tubes and Random Tech high flow cats, the gutted were
closer to the offroads than to the high-flows (there's a
post here about that, fairly old now). I found that after
swapping over to gutted, I had a higher logged dynamic
cylinder air readings at WOT. I see this as indicating less
backpressure, showing all the way up at the front (better
inhale from less residual gas in the cylinders, I figure).
SLP CME setup. I think it sounds pretty good. It does
have a little bit of boom to it at 2500RPM or so. I have
no rasp, I like to think because I dressed down all of
the sharp edges in the cat necks with a carbide burr
before installing. I flow-tested (ghetto style, leaf-blower
and vinyl-tubing manometer) the gutted cats vs offroad
tubes and Random Tech high flow cats, the gutted were
closer to the offroads than to the high-flows (there's a
post here about that, fairly old now). I found that after
swapping over to gutted, I had a higher logged dynamic
cylinder air readings at WOT. I see this as indicating less
backpressure, showing all the way up at the front (better
inhale from less residual gas in the cylinders, I figure).
11 Second Club
Joined: Feb 2005
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From: Alton IL
Nice, yea im still running stock headers, obviously, and it seems all the people with good cat back perfer the sound of no cats. I do have a good howl at 3k rpms, so i assume this will get louder, but i think im going to have to do it anyway, just for saftey sake of not clogging a cat.
long tube headers, off road y pipe and 80 series flowmasters here. Before the headers I took out the cats and put on the muffler. Many people asked me if I had the loudmouth exhaust. When I put the headers and y pipe on it made a night and day difference. At idle I am well defined, but not race car loud, just loud. I get heads turned everywhere I go and the cops usually here me coming at full thottle from a mile away before they actually see me. The interior noise is noticeable, but not near as loud as the exterior. I like mine a lot, but have been advised to get the GMMG chambered exhaust with my set up.
