Removing the Cat?
Junior Member
Joined: Mar 2006
Posts: 75
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Car: 1987 Pontiac GTA
Engine: 350tpi
Transmission: t56 6 speed
Axle/Gears: 3.70
Re: Removing the Cat?
You sure you wanna ask that on here? Some of these guy will tear you a knew one for even thinking it because of how illegal it is and all that stuff. I have done it and all i really noticed was a slight loss on mpg and exhaust didn't really get that much louder. How if you want go get one from magnaflow they are built really good and are high flow for about 100 or so.
Supreme Member
Joined: Jan 2007
Posts: 1,002
Likes: 12
From: Bastrop, TX
Car: 1988 SC Convertible
Engine: LT-1
Transmission: 700R4
Axle/Gears: 3.23 posi w/PBR's
Re: Removing the Cat?
How to fix one? - Take it off the car, with a pipe or piece or re-bar beat the honeycomb filling into small enough pieces so that they'll fit through the opening on each end, and re-install on the car. Take all the pieces from inside the cat to your local recycling yard to get $$$ for your next mod.
Senior Member
Joined: May 2008
Posts: 833
Likes: 0
From: London, Ont, Canada
Car: 87 T-Top GTA
Engine: 350 TPI
Transmission: 700R4
Axle/Gears: 3.27
Re: Removing the Cat?
Is there any HP gain? If so, would you get any HP by beating out the honeycomb filling? Or are you more likelly to get some HP with a Magnaflow Cat?
Yes I do know that this is illegal! Unless U use aftermarket Cat! (Right)?
Yes I do know that this is illegal! Unless U use aftermarket Cat! (Right)?
Last edited by y84pauloflondon; Sep 23, 2009 at 08:04 PM.
Senior Member
Joined: May 2008
Posts: 833
Likes: 0
From: London, Ont, Canada
Car: 87 T-Top GTA
Engine: 350 TPI
Transmission: 700R4
Axle/Gears: 3.27
Joined: Jul 1999
Posts: 10,950
Likes: 26
From: Orange, SoCal
Car: 1990 Pontiac Trans Am
Engine: 355 TPI siamesed runners
Transmission: Tremec T56
Axle/Gears: 12-Bolt 3.73
Re: Removing the Cat?
Having a hollow cat will probably cost you horsepower, as the hot exhaust has to expand into the shell and then shrink back down again to get out. That causes a restriction. It'll also sound "tinny" and "raspy" and be slightly louder.
Yes its totally illegal on a street car in the United States. Its better to replace it with an aftermarket cat. Its been dynoed the difference between a straight pipe and an aftermarket cat, and its about 2-3 horsepower at the wheels. But the difference it makes in the smell and harmful emissions from your exhaust is huge.
Yes its totally illegal on a street car in the United States. Its better to replace it with an aftermarket cat. Its been dynoed the difference between a straight pipe and an aftermarket cat, and its about 2-3 horsepower at the wheels. But the difference it makes in the smell and harmful emissions from your exhaust is huge.
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Joined: Jul 2001
Posts: 5,225
Likes: 70
From: Buffalo, NY
Car: 1988 IROC-Z
Engine: 427 SBC
Transmission: ProBuilt 700R4
Axle/Gears: Moser 12 Bolt / 3.73 TrueTrac
Re: Removing the Cat?
If you have the stock cat now.
Pros:
You will gain a little power (pipe it, don't just gut it)
It will be louder
It will be a bit more throaty
Cons:
It is illegal
Your exhaust smell will be quite a bit stronger and more potent
If your outside near your exhaust there's a very good chance your clothes will smell like it all day. Lol.
Pros:
You will gain a little power (pipe it, don't just gut it)
It will be louder
It will be a bit more throaty
Cons:
It is illegal
Your exhaust smell will be quite a bit stronger and more potent
If your outside near your exhaust there's a very good chance your clothes will smell like it all day. Lol.
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Banned
iTrader: (12)
Joined: Jul 1999
Posts: 12,212
Likes: 13
From: Bertram (outside Austin), TX
Car: 87 GTA
Engine: L98
Transmission: 700R4
Axle/Gears: Dana M78 3.27 posi
Re: Removing the Cat?
Correction.
Taking it off can......
get you a ticket
cause the inspection station to get investigated and/or fined
result in your registration being revoked
inspection sticker peeled ON THE SPOT
cause you to hafta pay to have it towed home
Need I say more?
Taking it off can......
get you a ticket
cause the inspection station to get investigated and/or fined
result in your registration being revoked
inspection sticker peeled ON THE SPOT
cause you to hafta pay to have it towed home
Need I say more?
Supreme Member
Joined: Mar 2009
Posts: 1,402
Likes: 3
From: Sussex County, NJ
Car: 1994 Z28
Engine: 355 LT1
Transmission: T56
Axle/Gears: 3.42
Re: Removing the Cat?
Gut it and repipe it... who cares about the environment or state emissions?
Then again, I also have no chance of passing emissions with that carb sitting under the hood of my "tune port injected" iroc.
Then again, I also have no chance of passing emissions with that carb sitting under the hood of my "tune port injected" iroc.
Supreme Member
iTrader: (17)
Joined: Nov 2005
Posts: 1,104
Likes: 2
From: Leicester,Massachusetts
Car: 1983 CHEVROLET CAMARO Z28
Engine: Forged 355 with a GT45 turbo
Transmission: TKO 600
Axle/Gears: built 4th gen rear with 3.27s
Re: Removing the Cat?
simple as what stephen said.... and the car looks sick stephen............
Senior Member
Joined: May 2008
Posts: 833
Likes: 0
From: London, Ont, Canada
Car: 87 T-Top GTA
Engine: 350 TPI
Transmission: 700R4
Axle/Gears: 3.27
Re: Removing the Cat?
Keep in mind that i live in canada and our laws are a bit diff. No cat is illegal...but I believe that any car 1987 or older does not need any emissions tests, anything newer will continue to get tested every other year. So really, I don't need to worry about inspections and stuff. (JUST SAYIN').
Banned
iTrader: (12)
Joined: Jul 1999
Posts: 12,212
Likes: 13
From: Bertram (outside Austin), TX
Car: 87 GTA
Engine: L98
Transmission: 700R4
Axle/Gears: Dana M78 3.27 posi
Re: Removing the Cat?
Keep in mind that i live in canada and our laws are a bit diff. No cat is illegal...but I believe that any car 1987 or older does not need any emissions tests, anything newer will continue to get tested every other year. So really, I don't need to worry about inspections and stuff. (JUST SAYIN').
Banned
iTrader: (12)
Joined: Jul 1999
Posts: 12,212
Likes: 13
From: Bertram (outside Austin), TX
Car: 87 GTA
Engine: L98
Transmission: 700R4
Axle/Gears: Dana M78 3.27 posi
Re: Removing the Cat?

https://www.thirdgen.org/forums/susp...els-315-a.html
Senior Member

Joined: Aug 2008
Posts: 710
Likes: 32
From: pensacola florida
Car: 1989 Firebird Formula
Engine: 5.7 LS1
Transmission: 4L60E
Axle/Gears: 3.27
Re: Removing the Cat?
Just get a high flow cat. You will probably get a little different exhaust sound and tone, and probably even gain a little mpg possibly. I cut my cat off my 94 silverado and i really regretted it, because i was making pit stops constantly, that thing lost so much mpg it wasnt funny.
Thats one reason why i havent cut the dual cats off my 91 TA, because people always tell me oh u only lose about a mile to the gallon. BULL****, unless you drive like a super grandma theres no way you milage will be the same. Even though i live in florida and dont have emissions either im still not cutting my cats off, ill replace them for high flows instead of cutting them anytime.
But the plus side.....
It really opened up my exhaust so much better, no more raddling in the cat cause mine was broke, and it sounded a lot more nasty and throaty, i really loved the exhaust sound, but you regret it in the long run once your use to it, and tired of it, and always having to go to the gas station, my truck was stock btw, no mods, that sucker just ate up gas after the cat was cut, and i put on a straight pipe to my flowmaster.
Thats one reason why i havent cut the dual cats off my 91 TA, because people always tell me oh u only lose about a mile to the gallon. BULL****, unless you drive like a super grandma theres no way you milage will be the same. Even though i live in florida and dont have emissions either im still not cutting my cats off, ill replace them for high flows instead of cutting them anytime.
But the plus side.....
It really opened up my exhaust so much better, no more raddling in the cat cause mine was broke, and it sounded a lot more nasty and throaty, i really loved the exhaust sound, but you regret it in the long run once your use to it, and tired of it, and always having to go to the gas station, my truck was stock btw, no mods, that sucker just ate up gas after the cat was cut, and i put on a straight pipe to my flowmaster.
Senior Member
Joined: May 2008
Posts: 833
Likes: 0
From: London, Ont, Canada
Car: 87 T-Top GTA
Engine: 350 TPI
Transmission: 700R4
Axle/Gears: 3.27
Re: Removing the Cat?
Is there any loss in mpg if using a aftermarket highflow cat? (ex. magnaflow, etc...)
From my understanding is, no loss in mpg and MAYBE a gain of 1-5 HP.(Stock engine, homemade cool air intake, manaflow muffler, belt is off my smog pump. that's all I got right now).
Thankx Guys.
From my understanding is, no loss in mpg and MAYBE a gain of 1-5 HP.(Stock engine, homemade cool air intake, manaflow muffler, belt is off my smog pump. that's all I got right now).
Thankx Guys.
Senior Member

Joined: Aug 2008
Posts: 710
Likes: 32
From: pensacola florida
Car: 1989 Firebird Formula
Engine: 5.7 LS1
Transmission: 4L60E
Axle/Gears: 3.27
Re: Removing the Cat?
As far as i know you wont really gain more mpg, maybe 1 mile at best with a new one. As far as horsepower, my buddy put a 3 inch magnaflow on his mustang, and he really didnt notice much power gain even dynoed.
Member

Joined: Mar 2008
Posts: 227
Likes: 0
From: RI
Car: 1989 GTA
Engine: 5.7 350
Transmission: 700R4
Axle/Gears: 3.23
Re: Removing the Cat?
In Mass. cars 1995 and older no longer need to pass emissions so i know of people that have taken them off. the question you have to ask yourself is why would you want to. Even though you can cut them it would be better to just add a high flow cat. They don't cut performance whatsoever and it will keep you from getting a hefty ticket if the cops ever look under your car.
Junior Member
Joined: Jun 2007
Posts: 75
Likes: 0
Car: 88 Formula
Engine: 305 TBI
Transmission: 700R4
Axle/Gears: 2.73
Re: Removing the Cat?
I've had no cat for like 5 years, no tickets, no problems, not a single shop has denied my inspection, it sounds way better with it off, so thats why I did it.
So what you said is ridiculous and i can guarantee probably will never happen, I've had one ticket in the last 5 years, and that was for "reving my engine/exhaust" right by a cop.
So whoever wants to replace the cat with a pipe, go right ahead, if you get failed on the inspection, go somewhere else tell you pass, simple, cops aren't going to get all dirty trying to look under a car for a cat, at least I've never heard of this happening in my state by any of my friends, or car club ( fastlouis )
As for california people, I'd just leave it on.
And I have no emissions here for pre-96, only visual "safety" inspection.
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