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Pros and Cons to gutting the Cat?

Pros and Cons to gutting the Cat?

Postby Kenmathis [OP] » Jul 05 2016, 6:53pm

Howdy! Before we start, I'm new to modifying trucks, so treat me with noob hands XD. MY truck is a 92 Sierra k1500 with a 5.7L 350, and a single inlet/dual outlet muffler already there, Im assuming the muffler is stock. I've been looking around and trying to decide the best way to modify my exhaust. Is there a con to gutting the cat so it acts as a straight pipe back? I dont mind a little drone so long as the truck isn't, though i dont want to muck with pressure so much that it bogs down when im accelerating. So, what are the cons, and what are the pros, to gutting the cat conv? And are there any legality issues surrounding that?
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92 K1500 SLE w/ Z71
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Re: Pros and Cons to gutting the Cat?

Postby PowerslavePA » Jul 05 2016, 8:14pm

Pros:
Better performance, not much, small HP increase, up to 5.
Better MPG
Breathes better.
Better fuel options.
Better sounding exhaust with the right mufflers.

Cons:
Is 100% Illegal, Federally, and in all states.
Noxious unburned gas fumes to the people behind you.
Lowers back pressure, shifts torque band upward in RPM range, if not towing, then who cares.
Will set a Check Engine Light, automatic failure instates that do emissions.
Will fail emissions test.
May sound like an echo chamber.
Longer engine warm-up period.
More carbon on bumper to clean off.

Modern Vehicles w/OBDII, removing a catalytic converter will not drastically increase vehicle performance without retuning.

Risks:
The chamber left after you would "gut" the cat may actually be worse at losing energy than a catalytic element.
This is because as the gases enter the empty chamber, exhaust velocity slows down. As it then regroups to
enter back into the exhaust piping, it does not have the energy it did before, therefore it "stacks", causing
backpressure. This backpressure now works against the flow of spent gases out of the cylinder when the
exhaust valve opens, causing the piston to do all the work. Now, energy is being wasted for gas removal
that could otherwise be used to turn the crankshaft.

Using a straight pipe (test pipe) would be better than gutting the oval container, for an up to 20HP gain..
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Re: Pros and Cons to gutting the Cat?

Postby 600doo » Jul 05 2016, 9:12pm

the tbi 350 is pretty gutless in design. but it does respond well to opening it up and letting it breath better. ive had an 89 and 92 tbi trucks, both got the cats replaced with straight pipe and single 3" exhaust with flow through muffler, run much better. there is no post cat o2 so you wont have an engine light, but it will fail a sniffer test.
2013 Sierra 1500 ECSB Z71 5.3L w/3.42s
-Airaid MIT
-Doug Thorley Tri-Y headers and ORY
-magnaflow single 3" exhaust
-BBP Tune
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Re: Pros and Cons to gutting the Cat?

Postby Kenmathis [OP] » Jul 06 2016, 3:30am

PowerslavePA wrote:Pros:
Better performance, not much, small HP increase, up to 5.
Better MPG
Breathes better.
Better fuel options.
Better sounding exhaust with the right mufflers.

Cons:
Is 100% Illegal, Federally, and in all states.
Noxious unburned gas fumes to the people behind you.
Lowers back pressure, shifts torque band upward in RPM range, if not towing, then who cares.
Will set a Check Engine Light, automatic failure instates that do emissions.
Will fail emissions test.
May sound like an echo chamber.
Longer engine warm-up period.
More carbon on bumper to clean off.

Modern Vehicles w/OBDII, removing a catalytic converter will not drastically increase vehicle performance without retuning.

Risks:
The chamber left after you would "gut" the cat may actually be worse at losing energy than a catalytic element.
This is because as the gases enter the empty chamber, exhaust velocity slows down. As it then regroups to
enter back into the exhaust piping, it does not have the energy it did before, therefore it "stacks", causing
backpressure. This backpressure now works against the flow of spent gases out of the cylinder when the
exhaust valve opens, causing the piston to do all the work. Now, energy is being wasted for gas removal
that could otherwise be used to turn the crankshaft.

Using a straight pipe (test pipe) would be better than gutting the oval container, for an up to 20HP gain..


Is it still illegal then to use straight pipe? And would lining the walls of a section of the straight pipe with a thin amount of the existing catalyst material be enough to get the vehicle to pass a sniffer test, while still retaining the benefits(to a reasonable degree) of running straight pipe instead of a cat? A bit off from the original topic, but what you said got me thinking. Not a challenge, just a question. Guess could prolly run dual outlets and straight pipe for a greater HP gain than stated?
What did you mean by better fuel options?
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92 K1500 SLE w/ Z71
Cooper MTP's 285/75/16 on MB Chaos 6 Spoke wheels

Ask and ask and ask till you get it right.
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Re: Pros and Cons to gutting the Cat?

Postby Kenmathis [OP] » Jul 06 2016, 3:38am

600doo wrote:the tbi 350 is pretty gutless in design. but it does respond well to opening it up and letting it breath better. ive had an 89 and 92 tbi trucks, both got the cats replaced with straight pipe and single 3" exhaust with flow through muffler, run much better. there is no post cat o2 so you wont have an engine light, but it will fail a sniffer test.


The lack of a check engine light as a result of cat delete does lighten my worry. But what is breathing better as a result of cat delete?
What is a flow through muffler? And can I, as responded to PowerslavePA's post, rectify the failed sniffer test by lining the walls of a section of pipe with the existing catalyst material, while retaining(to a reasonable degree) the benefits following a cat delete? This isn't something that is a make-or-break for deleting the cat, but it would be interesting to see if that were possible
Image

92 K1500 SLE w/ Z71
Cooper MTP's 285/75/16 on MB Chaos 6 Spoke wheels

Ask and ask and ask till you get it right.
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Re: Pros and Cons to gutting the Cat?

Postby ericlw » Jul 06 2016, 3:49am

Is it still illegal then to use straight pipe? 100% illegal

And would lining the walls of a section of the straight pipe with a thin amount of the existing catalyst material be enough to get the vehicle to pass a sniffer test, while still retaining the benefits(to a reasonable degree) of running straight pipe instead of a cat?


you are kidding right?
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Re: Pros and Cons to gutting the Cat?

Postby Kenmathis [OP] » Jul 06 2016, 4:03am

ericlw wrote:Is it still illegal then to use straight pipe? 100% illegal

And would lining the walls of a section of the straight pipe with a thin amount of the existing catalyst material be enough to get the vehicle to pass a sniffer test, while still retaining the benefits(to a reasonable degree) of running straight pipe instead of a cat?


you are kidding right?


Wasn't kidding. As I said, I'm new to this. I imagine by your response that my suggestion would not work?
Image

92 K1500 SLE w/ Z71
Cooper MTP's 285/75/16 on MB Chaos 6 Spoke wheels

Ask and ask and ask till you get it right.
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Re: Pros and Cons to gutting the Cat?

Postby silverado9306 » Jul 06 2016, 5:01am

My 93 has been straight piped from the headers back for 10 years or better now, no issues with it what so ever. My state doesn't check the exhaust if it's over a certain age but I know a guy...

Check your state laws about before you go for it.
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Re: Pros and Cons to gutting the Cat?

Postby Onlyina_Chevy » Jul 06 2016, 5:38am

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Re: Pros and Cons to gutting the Cat?

Postby 600doo » Jul 06 2016, 1:36pm

Kenmathis wrote:
600doo wrote:the tbi 350 is pretty gutless in design. but it does respond well to opening it up and letting it breath better. ive had an 89 and 92 tbi trucks, both got the cats replaced with straight pipe and single 3" exhaust with flow through muffler, run much better. there is no post cat o2 so you wont have an engine light, but it will fail a sniffer test.


The lack of a check engine light as a result of cat delete does lighten my worry. But what is breathing better as a result of cat delete?
What is a flow through muffler? And can I, as responded to PowerslavePA's post, rectify the failed sniffer test by lining the walls of a section of pipe with the existing catalyst material, while retaining(to a reasonable degree) the benefits following a cat delete? This isn't something that is a make-or-break for deleting the cat, but it would be interesting to see if that were possible


the less restriction via the intake and exhaust of that engine the better. flow through muffler like a magnflow or similar, not a chambered muffler. If you need to pass emissions with a vehicle that doesn't have obd2 you have no options but to leave the cat. however if it is original, i would replace it with a new magnaflow universal one.
2013 Sierra 1500 ECSB Z71 5.3L w/3.42s
-Airaid MIT
-Doug Thorley Tri-Y headers and ORY
-magnaflow single 3" exhaust
-BBP Tune
Image
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