Pros & Cons of cat gutting.....

DZEE'S LX · 03-28-2002, 07:29 PM

And not neccesarily the feline variety......

I already know that I should be doing a offroad pipe or new high flow cat h-pipe, but I'm wondering if this will work for now until I have the money.

While fixing one of my cracked pipes, the guy at the muffler shop was doing his best to convince me that they could build a custom 2.5 X-pipe behind the cats and then go 2.5 mandrel-bent to the bumper. So now I'm thinking about gutting the two rear cats assuming that they start the new pipe right at the back of each cat. I think the shop will look the other way if I do this myself.

I'm trying to achieve three things.
1. Just a little louder sound out of my Race Magnum mufflers.
2. Passing the visual part of the emissions test.
3. Hoping that the two front cats are enough to help pass the sniff test.

Has anyone done this? How much does it change sound and did you still pass smog?

Oh, if you work for the EPA this is only an idea and I will never actually do it

!!!

sn95gt19 · 03-28-2002, 11:54 PM

i have a 95 gt and i gutted the front two cats and had the muffler shop make a 2.5in. piece to go to the mufflers so the two front chambers are only there, this made my car sound a lot louder when your on it but really quiet at idle, it also has a very deep sound to it with 2 chamber flows/2.5in tail pipes, with stock headers, my car obviously doesnt pass the emissions cause i have NO cats but i would think it would pass cause they sell the aftermarket ones with only two.

PKRWUD · 03-29-2002, 12:36 AM

You only have two cats. The "first two" are pre-cats, and have a minimal effect on the emissions. It's the "back two" cats that do all the work. Without them, I don't see you passing the sniffer unless they test the car with the engine shut off.

Take care,
-Chris

DZEE'S LX · 03-29-2002, 02:24 PM

Does anyone know exactly what the converters actually do to the exhaust that "cleans" up the emmissions? Is it like CO or hydrocarbons or whatever?
Is it true that a well tuned engine can pass the tailpipe test without cats?

PKRWUD · 04-01-2002, 11:35 PM

I'm not a chemist, but basically the cats turn the HC and CO into H2O.

Take care,
-Chris

sn95gt19 · 04-01-2002, 11:42 PM

i never knew that there were only 2 "real" cats and the first two were only pre-cats, when i hollowed them out the front two had the same exact insides as the rear two, i always wondered how they could get away with only putting two cats on aftermarket pipes, i just dont understand how they could be pre-cats when they both have the same insides. if you want to explain it, im up for learning something new

PKRWUD · 04-02-2002, 12:54 AM

Quote:

Originally posted by sn95gt19
i never knew that there were only 2 "real" cats and the first two were only pre-cats, when i hollowed them out the front two had the same exact insides as the rear two, i always wondered how they could get away with only putting two cats on aftermarket pipes, i just dont understand how they could be pre-cats when they both have the same insides. if you want to explain it, im up for learning something new

The honeycomb in the pre-cats is coated with a rhodium/platinum catalyst, while the honeycomb in the regular cats is coated with a platinum/palladium catalyst. The pre-cats "work" when the exhaust is too cold for the regular cats to be effective, but really only do a halfassed job.

Take care,
-Chris

Unit 5302 · 04-02-2002, 01:05 AM

The catalytic converters have platinum, which is a catalyst to complete the burning of any raw fuel being dumped into the exhaust. That's why they get so crazy hot when you're running too rich, and they plug with carbon and other byproducts when you lack enough outside air being pumped from the smog pump.

Yes, a well tuned car can pass emissions in most cases with no cats because a car in excellent tune will not have a lot of unburned fuel going out the exhaust. I've seen it done before several times. My dad had a 1978 Lincoln Town Car with the 460. The cats were all hollow and every piece of emissions equipment on the car had been disabled. It passed after a run up. Keep in mind, it got 8-10mpg in town and 13-15 on the highway. It burned a LOT of fuel. That being said, a 5.0HO with it's aggressive camshaft really needs to be running great to do it.

PKRWUD · 04-02-2002, 01:21 AM

Quote:

Originally posted by Unit 5302
Yes, a well tuned car can pass emissions in most cases with no cats because a car in excellent tune will not have a lot of unburned fuel going out the exhaust. I've seen it done before several times. My dad had a 1978 Lincoln Town Car with the 460. The cats were all hollow and every piece of emissions equipment on the car had been disabled. It passed after a run up. Keep in mind, it got 8-10mpg in town and 13-15 on the highway. It burned a LOT of fuel. That being said, a 5.0HO with it's aggressive camshaft really needs to be running great to do it.

Also keep in mind that the numbers allowed for passing are alot greater for a 1978 vehicle than they are for a 1986 or newer vehicle.

Take care,
-Chris

chatcher · 04-02-2002, 07:30 PM

haste makes waste save up get an h or x pipe that way you can switch back come sniff time

joe4speed · 04-02-2002, 10:19 PM

Move to FL, they got rid of that crap a couple years ago, much to my happiness!! Now I don't have to crawl under the car every year to put the cats on!

Topless In Texas · 04-03-2002, 01:08 AM

Quote:

Originally posted by chatcher
haste makes waste save up get an h or x pipe that way you can switch back come sniff time

**either that, or become friends w/ the guys at the local inspection place, when they will just slap a sticker on it cuz they like your car!!**

03-28-2002, 07:29 PM	#1
DZEE'S LX Registered Member Join Date: Jan 2001 Location: Salt Lake City Posts: 117	Pros & Cons of cat gutting..... And not neccesarily the feline variety...... I already know that I should be doing a offroad pipe or new high flow cat h-pipe, but I'm wondering if this will work for now until I have the money. While fixing one of my cracked pipes, the guy at the muffler shop was doing his best to convince me that they could build a custom 2.5 X-pipe behind the cats and then go 2.5 mandrel-bent to the bumper. So now I'm thinking about gutting the two rear cats assuming that they start the new pipe right at the back of each cat. I think the shop will look the other way if I do this myself. I'm trying to achieve three things. 1. Just a little louder sound out of my Race Magnum mufflers. 2. Passing the visual part of the emissions test. 3. Hoping that the two front cats are enough to help pass the sniff test. Has anyone done this? How much does it change sound and did you still pass smog? Oh, if you work for the EPA this is only an idea and I will never actually do it!!! __________________ Spec Service (UHP), BFG G-Force KDW's, Turbo Coupe 3.55 rear w/disks, 73mm calipers, Stg 1 Twisted Wedges, TFS Street Intake, 70mm TB, E cam, Crane 1.7's, Aeromotive FPR, BBK 1 5/8 shorties, elec fan, FMS Al Radiator, Moroso Wires, Kenne Bell Ramair, March pulleys, Race Magnums, 190 lph Walbro, FMS Al Dshaft, D/S loop, MM 4point rollbar, FMS C spngs, strut tower brace, Tokico Illuminas, Prothane bushings, MM Lwr Conrol Arms, KB welded subs, Cervini Mach 1 hood/valence/side skirts/wing/airdam.

03-29-2002, 12:36 AM	#3
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	You only have two cats. The "first two" are pre-cats, and have a minimal effect on the emissions. It's the "back two" cats that do all the work. Without them, I don't see you passing the sniffer unless they test the car with the engine shut off. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

03-29-2002, 02:24 PM	#4
DZEE'S LX Registered Member Join Date: Jan 2001 Location: Salt Lake City Posts: 117	Does anyone know exactly what the converters actually do to the exhaust that "cleans" up the emmissions? Is it like CO or hydrocarbons or whatever? Is it true that a well tuned engine can pass the tailpipe test without cats? __________________ Spec Service (UHP), BFG G-Force KDW's, Turbo Coupe 3.55 rear w/disks, 73mm calipers, Stg 1 Twisted Wedges, TFS Street Intake, 70mm TB, E cam, Crane 1.7's, Aeromotive FPR, BBK 1 5/8 shorties, elec fan, FMS Al Radiator, Moroso Wires, Kenne Bell Ramair, March pulleys, Race Magnums, 190 lph Walbro, FMS Al Dshaft, D/S loop, MM 4point rollbar, FMS C spngs, strut tower brace, Tokico Illuminas, Prothane bushings, MM Lwr Conrol Arms, KB welded subs, Cervini Mach 1 hood/valence/side skirts/wing/airdam.

04-01-2002, 11:35 PM	#5
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	I'm not a chemist, but basically the cats turn the HC and CO into H2O. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

04-02-2002, 07:30 PM	#10
chatcher Registered Member Join Date: Jun 2001 Location: butler pa Posts: 303	haste makes waste save up get an h or x pipe that way you can switch back come sniff time __________________ 92lx wannabe saleen

03-28-2002, 11:54 PM	#2
sn95gt19 motors done......woohooo Join Date: Mar 2002 Posts: 799	i have a 95 gt and i gutted the front two cats and had the muffler shop make a 2.5in. piece to go to the mufflers so the two front chambers are only there, this made my car sound a lot louder when your on it but really quiet at idle, it also has a very deep sound to it with 2 chamber flows/2.5in tail pipes, with stock headers, my car obviously doesnt pass the emissions cause i have NO cats but i would think it would pass cause they sell the aftermarket ones with only two.

04-01-2002, 11:42 PM	#6
sn95gt19 motors done......woohooo Join Date: Mar 2002 Posts: 799	i never knew that there were only 2 "real" cats and the first two were only pre-cats, when i hollowed them out the front two had the same exact insides as the rear two, i always wondered how they could get away with only putting two cats on aftermarket pipes, i just dont understand how they could be pre-cats when they both have the same insides. if you want to explain it, im up for learning something new

04-02-2002, 01:05 AM	#8
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	The catalytic converters have platinum, which is a catalyst to complete the burning of any raw fuel being dumped into the exhaust. That's why they get so crazy hot when you're running too rich, and they plug with carbon and other byproducts when you lack enough outside air being pumped from the smog pump. Yes, a well tuned car can pass emissions in most cases with no cats because a car in excellent tune will not have a lot of unburned fuel going out the exhaust. I've seen it done before several times. My dad had a 1978 Lincoln Town Car with the 460. The cats were all hollow and every piece of emissions equipment on the car had been disabled. It passed after a run up. Keep in mind, it got 8-10mpg in town and 13-15 on the highway. It burned a LOT of fuel. That being said, a 5.0HO with it's aggressive camshaft really needs to be running great to do it.

04-02-2002, 10:19 PM	#11
joe4speed He said Member...heh, heh Join Date: Sep 1999 Location: Jupiter, Florida U.S.A. Posts: 3,718	Move to FL, they got rid of that crap a couple years ago, much to my happiness!! Now I don't have to crawl under the car every year to put the cats on! __________________ *Joe!* 1988 GT, 13.58@101mph Check out my listing! Click here! Or my website:www.joe4speed.com

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