Cat or no Cat?

[PlayingWithTBI]

As a personal preference, I like to keep the cat.

I run cats as well. The modern high flows do not cost any power and the vehicle will not smell like an old lawnmower.

The pellet-style cats were restrictive when new. Modern cats are honeycomb/monolithic and not as restrictive.

You can add me to that list!

You might as well cram a high-flow "Y" pipe, high-flow catalyst, and big pipes back to the muffler and tailpipe.
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That's what I did with my 88, with a Borla Pro XS straight through, 3" all the way from the "Y" pipe. Here's the JBL "Y" and a high flow Cat I used. I probably added 10+ HP, maybe 20, who knows.

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Here's the difference between the Borla and my old "Pro Flow" muffler with 3" exhaust.

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[letitsnow]

I run my K2500 without cats. Not due to thinking that the cats cause a performance loss, it is just to keep it as simple as possible.

As far as the air pollution created without cats - unless we can find a way to eliminate the constant wildfire smoke, it probably doesn't matter.

 

[Leeztruk]

When I built my exhaust system, it was 2 1/2" to the Y then 3" single pipe/cat/muffler/tailpipe

 

[1998_K1500_Sub]

When I built my exhaust system, it was 2 1/2" to the Y then 3" single pipe/cat/muffler/tailpipe

Was that a kit or something you assembled from the various parts?

 

[Leeztruk]

Various vendors. Muffler and tailpipe are Walker, cat is hi-flow from ebay, Y and front pipes from Summit. Making the complete front Y section was the hardest and most time consuming. I did this for my LS swap, but a set-up for a SBC would be similar

 

[s98gmc]

Part of "not getting our hobby banned" is being honorable and doing the right thing. WCJr came to me straight-piped, and I spent the money to put cats on it. Roscoe was straight piped as well, and when I build the exhaust for it, it will have cats as well.

I agree. The previous owner of my step side had installed a Y pipe without cats and one of the first things I did was have a shop add some. I needed cats to pass inspection and a side benefit is there is much less droning and noise. Antique registration was an option and I've been asked why I didn't, but there are usage rules that go with those plates. I didn't want to deal with that.

 

[1989GMCSIERRA]

To remove your cats, you will need to ether tune the rear 02 sensors out, or make a set of these. If you don't, you will trip the CEL. Thread 'remove your cats, and make a mini cat for your rear 02 sensors.' https://www.gmt400.com/threads/remove-your-cats-and-make-a-mini-cat-for-your-rear-02-sensors.30681/

1989 doesn’t have a rear sensor. Most likely (if it’s factory) he has to have a pancake cat con. and it’s restrictive as hell new so I cant imagine how it is now. The factory system is crap to begin with.

for a quick and dirty remove o2 sensor and see if you gained power. It could also be a internally collapsed muffler since it sounds like its a original exhaust system


as far as removal…it’s not legal ….as it’s tampering with emission system. Can it be done….sure. But a good header kit and 3 inch mandrel bent aftermarket system with cats will imo be a better way to go instead of patch bubblegum, wire and spit trying to use a 34/35 year old exhaust system.

 

[jaybee]

Another vote to keep a cat in the system. Aftermarket, high flow cats aren't ridiculously expensive, they flow plenty for the application, and they'll keep you legal. Coal rolling diesels are endangering the ability of everyone to modify their vehicles responsibly. No sense in asking for legal trouble, even if in your area you're unlikely to find it.

 

[Moofus02]

When I built my exhaust system, it was 2 1/2" to the Y then 3" single pipe/cat/muffler/tailpipe

I like the merge on that y pipe

 

[Erik the Awful]

It could also be a internally collapsed muffler since it sounds like its a original exhaust system

Back when I was a Nissan tech, we had a 300ZX Turbo come in for an injector recall that was running like absolute dog-butt. I dropped the exhaust behind the down pipe and used a coat hanger to secure it up and drove it around the back lot. It ran hard. The cat was clogged.

When I got WCJr and installed my engine in it, it ran like dog-butt and splattered mud behind the driver's exhaust, nothing behind the passenger. I dropped that side behind the manifold and the engine ran strong. The tailpipe was full of mud. It got a new full exhaust with an O2 sensor bung welded into the driver's collector and inexpensive Walker cats from Summit right after the collectors.