Gutting Cats
#1
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Car: 1991 Trans AM GTA
Engine: 5.7L TPI
Transmission: 700R4
Gutting Cats
Can anyone help me figure out what is needed to be done in order to gut the cats? I am putting Hedman Hedders on my 91 GTA 5.7L and am going to run true dual exhaust.
Another question, would it be better to run cats or just go w/o the cats, I am in Oklahoma and we no longer have emissions tests.
Thanks for the comments.
John
Another question, would it be better to run cats or just go w/o the cats, I am in Oklahoma and we no longer have emissions tests.
Thanks for the comments.
John
#2
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well if ur going with true duals it sounds easier to do away with the cats one less tihng to worry about, and since u dont even get tested then thats another plus.
i would just run the headers and worry about getting the true duals with out any cats under the car nicely.
i would just run the headers and worry about getting the true duals with out any cats under the car nicely.
#3
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Car: 1991 Trans AM GTA
Engine: 5.7L TPI
Transmission: 700R4
I have been told that our cars have to have the cats in order to run right, because w/o them there will not be enough backpressure getting to the motor.
the only problem i have w/ running without a cat is that there is noone around that will do the exhaust w/o the cat since it already has one on it.
the only problem i have w/ running without a cat is that there is noone around that will do the exhaust w/o the cat since it already has one on it.
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Car: Still a 3rd Gen
Engine: 450HP 355
Transmission: TH350
Axle/Gears: 9" with 4.11's
LOL, go to Autozone, rent the pipe cutter and hack them off. then drive it to the muff shop and tell them what you want done. hell, just to be safe you could hack off the whole system. that way they would never know.
just tell them you bought it like that
You don't need cats. it'll run way better w/o them then with gutted ones. a gutted cat dosen't flow very good. I've heard that because of the shape a small vortex forms in the center and can kill like 30% of the flow on a gutted cat.
just make sure you pinch off the air tube that runs to the cat.
Dave
just tell them you bought it like that
You don't need cats. it'll run way better w/o them then with gutted ones. a gutted cat dosen't flow very good. I've heard that because of the shape a small vortex forms in the center and can kill like 30% of the flow on a gutted cat.
just make sure you pinch off the air tube that runs to the cat.
Dave
Last edited by DeathStarr89; 12-14-2003 at 04:03 PM.
#5
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Car: '87 Z
Engine: 355 in the works
Transmission: 700R4
Hi fellow oklahoman, what part are you in? I'm running without a cat and my car runs fine... sounds alot better then the gutted cat it had before also...
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Car: 1991 Trans AM GTA
Engine: 5.7L TPI
Transmission: 700R4
Originally posted by Hg
Hi fellow oklahoman, what part are you in? I'm running without a cat and my car runs fine... sounds alot better then the gutted cat it had before also...
Hi fellow oklahoman, what part are you in? I'm running without a cat and my car runs fine... sounds alot better then the gutted cat it had before also...
#7
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Car: 1991 Z-28
Engine: Can you say stroke?!?!
Transmission: 700-r4
Axle/Gears: 3.42
Run with gutted cats. All you need to do is cut the cat off, gut it, then push a 2 1/4 inch pipe through it, and then install it. This way you have the appearance of a cat on the outside and nothing but free flowing exhaust on the inside. Do a search on the subject, it has been beat to death.
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#8
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Car: '87 Z
Engine: 355 in the works
Transmission: 700R4
I'm in Midwest City. I had a shop put my exhaust on since it was all original/rusted/corroded together. He kept the cat, but later I went to a shop I know will do things like this and had a piece of pipe put in place of my cat...
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Car: 1991 Trans AM GTA
Engine: 5.7L TPI
Transmission: 700R4
Originally posted by Hg
I'm in Midwest City. I had a shop put my exhaust on since it was all original/rusted/corroded together. He kept the cat, but later I went to a shop I know will do things like this and had a piece of pipe put in place of my cat...
I'm in Midwest City. I had a shop put my exhaust on since it was all original/rusted/corroded together. He kept the cat, but later I went to a shop I know will do things like this and had a piece of pipe put in place of my cat...
john
#10
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you don't need cats to run anything....ever....did care back in the day not run right because of a lack of cats? nope....also back then you could walk into a parts store and buy a "test pipe" to check to see if you're cat was clogged. So many people bought test pipes....wouldn't you know it....eventually there were some really rusted out "test pipes" on cars.
good luck and ditch that cat...
good luck and ditch that cat...
#11
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Car: '84 Camaro SC/ I-ROC Body Conversio
Engine: Rebuilt 350 5.7L, Edelbrock 750cfm
Transmission: Re-built 700-R4
Axle/Gears: Moser, 3.73
Drop the CAT down at the rear bolts and take a solid pry bar or something long, sharp, and thick and run it through and just suck all the broken pieces out with a vacuum or pull them out with your hands.
I did it to mine and I'm an Emissions Inspector! hehehe
I did it to mine and I'm an Emissions Inspector! hehehe
#12
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Car: '87 Z
Engine: 355 in the works
Transmission: 700R4
My car runs just fine without it, and sounds alot meaner with the straight pipe versus gutted cat.
#13
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Car: 1989 TTA
Engine: LC2
Transmission: Worn-out 200R4
Axle/Gears: BW 9-bolt, 3.27's
Backpressure - call me stupid, but isn't backpressure a BAD thing? Wouldn't it be better to reduce backpressure, to improve exhaust gas scavenging? I would think that backpressure makes the engine work harder to force the exhaust out of teh engine and through the exhaust system, thus (if my logic is correct) if you reduce backpressure, you reduce useless load on the engine, right?
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Car: 1991 Trans AM GTA
Engine: 5.7L TPI
Transmission: 700R4
Originally posted by pvt num 11
Backpressure - call me stupid, but isn't backpressure a BAD thing? Wouldn't it be better to reduce backpressure, to improve exhaust gas scavenging? I would think that backpressure makes the engine work harder to force the exhaust out of teh engine and through the exhaust system, thus (if my logic is correct) if you reduce backpressure, you reduce useless load on the engine, right?
Backpressure - call me stupid, but isn't backpressure a BAD thing? Wouldn't it be better to reduce backpressure, to improve exhaust gas scavenging? I would think that backpressure makes the engine work harder to force the exhaust out of teh engine and through the exhaust system, thus (if my logic is correct) if you reduce backpressure, you reduce useless load on the engine, right?
I think I am going to run w/o cats if i can find someone that will put the exhaust on for me and not hassle me about it being against the law to take the cats off.
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Car: Still a 3rd Gen
Engine: 450HP 355
Transmission: TH350
Axle/Gears: 9" with 4.11's
Originally posted by White91GTA
That is the same thing that I thought. I asked my dad about it and he said if what i was told about GM products needing the backpressure was true, then why is his truck running better w/o the cat than it was before.
I think I am going to run w/o cats if i can find someone that will put the exhaust on for me and not hassle me about it being against the law to take the cats off.
That is the same thing that I thought. I asked my dad about it and he said if what i was told about GM products needing the backpressure was true, then why is his truck running better w/o the cat than it was before.
I think I am going to run w/o cats if i can find someone that will put the exhaust on for me and not hassle me about it being against the law to take the cats off.
It's not backpressure that can make or break HP curves in performance, it's exhaust velosity. You want the smoothest flowing exhaust possible however using too big of pipes will cause the scavengeing to be too much. you want to ge the exhaust away from the engine as quick as possible. too small of pipes will cause a restriction and overpressure the exhaust system, too big of pipes and the exhaust will move as a slow rate of speed. you need to choose the propper diameter for your performance level. ie: a 500HP BBC would run best with 3" duals, however a 350HP SBC would probably run best with 2.5" duals.
It's all deturmined by the setup of the pipes, headers and your engine build.
I Put 3" true duals on a stock '68 327 in a 79 regal. it ran like dog sh*t. then i swapped out the 3" for 2.25" and it ran way better.
Of course, anything over 500 or 600HP would probably run best un-capped
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Car: '84 Camaro SC/ I-ROC Body Conversio
Engine: Rebuilt 350 5.7L, Edelbrock 750cfm
Transmission: Re-built 700-R4
Axle/Gears: Moser, 3.73
It's like this... GM and other car manufacturers say a car "runs better w/ CATs" meaning it runs CLEANER. But as far as we are concerned and as far as PERFORMANCE is concerned, flow is more important and the less resistance you have (ie. CATs, restrictive exhaust pipes) the more potential you car has to breathe allowing for it to have a little more giddy-up
#17
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Car: 1989 TTA
Engine: LC2
Transmission: Worn-out 200R4
Axle/Gears: BW 9-bolt, 3.27's
Good, Hawaii has no smog-check (even though you can always find smog-test wonder juice at Wal-Mart...) so I'm looking to get duals w/o cats.
#18
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Car: 83 z28
Engine: L69
Transmission: BW t-5
If your worried about not having the cat "appearance", couldn't you take the cat off, cut it in half, rip everything out, and weld in a pipe where the cat was, then weld the cat shells back on. Could that be done? Just a suggestion.
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Car: 82 z28
Engine: 355
Transmission: 350
When I hollowed out my cat my car seems to lose power . I would'nt say it sounded too great either . I was told the same thing that purple82 mentioned , the bigger open chamber causes turbulance makeing velosity slow down . You want the exaust to exit as fast as possible so " scavageing " occurs . When the right amount of air is confined just enough it tends to move much faster . That also helps to pull the the intake charge through .
A friend of mine trimmed the extra pipe off my cat and streched it out just enough to put a 3" piece through and welded it . A few coats of aluminized paint and it blends in perfect . So far I've had 2 cops look under my car and I have'nt gotten a single ticket .
A friend of mine trimmed the extra pipe off my cat and streched it out just enough to put a 3" piece through and welded it . A few coats of aluminized paint and it blends in perfect . So far I've had 2 cops look under my car and I have'nt gotten a single ticket .
#20
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Car: 1988 Trans Am GTA Notchback
Engine: 305ci, 5.0L, TPI, HO
Transmission: Borg Warner T5 5-Speed
Axle/Gears: 9-Bolt Positraction Rear w/3.45 Grs
Originally posted by CbrasTsteLkChk
Drop the CAT down at the rear bolts and take a solid pry bar or something long, sharp, and thick and run it through and just suck all the broken pieces out with a vacuum or pull them out with your hands.
I did it to mine and I'm an Emissions Inspector! hehehe
Drop the CAT down at the rear bolts and take a solid pry bar or something long, sharp, and thick and run it through and just suck all the broken pieces out with a vacuum or pull them out with your hands.
I did it to mine and I'm an Emissions Inspector! hehehe
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