Bringing the Cat back...enough is enough.

SquareRoot

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First off to all the haters, to each their own. I'm not a tree-hugger by any means but I do appreciate being able to breathe clean air around MY truck. Some facts: 85 K20, 350, Port fuel injection, NV4500.

Currently has Hedman headers, 2-1/2" true dual exhaust out the back thru Flowmaster 50 series mufflers. It looks great and sounds good.

This truck is an off-road and work truck. It doesn't get drag raced and you don't be shifting NV4500's at 6000 rpm. I seriously doubt with all the performance parts it puts out more than 350hp on a good day. I am perfectly satisfied with its performance for how I use it. With all that said, it has a serious drawback that I can no longer stand- The Stinky A** exhaust! And before you say it, it's NOT running rich, I am very educated on the Air/Fuel ratios and their effects on the Carbon Monoxide CO, Nitrogen Oxides NOx, and Hydrocarbon HC. EFI alone does not eliminate these. Sorry they are byproducts of the combustion process.

So what I'm gonna do is retain the headers and hopefully figure out a way to add a Y-Pipe and a 3-way converter somewhat like the factory did. I don't know what that is in a 4wd because my truck has never had it. I also don't like the current 2 1/2" pipe on the passenger side because it snakes under the crossmember and runs parallel with the fuel lines.

My thoughts are to run 2 1/4" pipe for the Y-pipe into a 3 inch single pipe down the drivers side and out behind the d/s rear tire. I am going to invest in a good muffler, Borla most likely.

My biggest concern is getting the Cat close enough to the Y-so that it gets hot enough to fire off and work properly. If that cant happen the whole thing is a moot point. I'm concerned the headers are going to shed heat and contribute to my demise?

Can someone tell me where exactly the factory cat was located? Is anyone out there running headers and cats? I know there is a myriad of aftermarket cats out there but the location and exhaust temp limitations really got me perplexed. I'm not opposed to replacing the headers with ceramic coated ones if that's part of the solution.
 

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SirRobyn0

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@SquareRoot You won't get no hatred from me. In fact if I could like your post multiple times I would. So my motor is lower output than yours, but what I'm running, is 2 1/4" Y-pipe, to high flow cat, mid-pipe is a 3 1/2", I'm running a walker sound FX muffler on the drivers side with dual 2 1/4 exits, both on the drivers side. The reason for the dual exits is just less restriction and since I could get a muffler with single entrance dual exits anyway I figured why not. Sound is quiet but good. Factory location is where I'm running mine, just right after the Y-comes together, but as you know the closer to the manifold the better. Also bear in mind the modern universal cats are light years ahead of where the old ones were, so even if it's not in the ideal location, it'll work, it just might take longer to get fully warmed up and fully functional.

One think I'll add you your reasons to run a cat is NOx, you did meantion it, but here is a fun fact. NOx is really good at destroying lung tissue.
 

SquareRoot

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@SquareRoot You won't get no hatred from me. In fact if I could like your post multiple times I would. So my motor is lower output than yours, but what I'm running, is 2 1/4" Y-pipe, to high flow cat, mid-pipe is a 3 1/2", I'm running a walker sound FX muffler on the drivers side with dual 2 1/4 exits, both on the drivers side. The reason for the dual exits is just less restriction and since I could get a muffler with single entrance dual exits anyway I figured why not. Sound is quiet but good. Factory location is where I'm running mine, just right after the Y-comes together, but as you know the closer to the manifold the better. Also bear in mind the modern universal cats are light years ahead of where the old ones were, so even if it's not in the ideal location, it'll work, it just might take longer to get fully warmed up and fully functional.

One think I'll add you your reasons to run a cat is NOx, you did meantion it, but here is a fun fact. NOx is really good at destroying lung tissue.
I like your setup. I could do the dual exit. Where exactly is your cat located, under the D/S seat area? Actually my wife has developed a chronic lung disease (Hypersensitivity pneumonitis) in the past few years. She was washing her car yesterday when I drove up in the truck and she started coughing so bad it made me feel like S**T.

Thanks for the reply.
 

gotyourgoat

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BTW an oem single exhaust has the cat starting basically at/just behind where the speedo cable enters trans(350) or at the back edge of the trans crossmember(c10).

It is too dark and cold for pics.
 

waterpirate

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My cat on the 87 short bed was attached to the y pipe via a 4" adapter from the factory.
Eric
 

SirRobyn0

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I like your setup. I could do the dual exit. Where exactly is your cat located, under the D/S seat area? Actually my wife has developed a chronic lung disease (Hypersensitivity pneumonitis) in the past few years. She was washing her car yesterday when I drove up in the truck and she started coughing so bad it made me feel like S**T.

Thanks for the reply.
My Cat is directly behind transmission cross member, as gotyourgoat said near the speedocable.

Ya, for a while I wanted to put dual exhaust on the truck, but after doing the larger single, I no longer have any interest in a dual setup. I have lung issues to and to much exhaust, or just a short time in strong exhaust will have me pumping on my inhaler. Even though my truck is carbureted the exhaust does not bother me once it's warmed up. When it's cold I have to stay out of the main stink though....
 

Catbox

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I know it is a different vehicle, but this is what the Y pipe off my 1995 Suburban looks like. Just about as soon as you can, put the cat there.
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This is what replaced it as the aftermarket cat that is above was blown out by some substantial backfiring issues we had a few months ago and we couldn't pass DEQ.
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With this new Flowmaster Cat, we passed with flying colors.

Maybe a set of 3/4 length headers would help facilitate the cat location on your truck.
 

shinkle

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I just added a Cat back to my truck with a new muffler and new pipe. The cat is located just past the Y and I think there is some type of heat shield at the location. A local shop put 2 1/2" pipe from the Y back. Here is a diagram of stock. Click on pic
 

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SquareRoot

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Another benefit I just thought of is having the O2 sensor reading both sides of the engine rather than just one bank of cylinders.
 

Turbo4whl

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Don't forget to add the heat shield above the convertor. The factory would not have wasted the money if it wasn't needed.
 

SirRobyn0

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Don't forget to add the heat shield above the convertor. The factory would not have wasted the money if it wasn't needed.
Yea, that's a good point my truck has one. @SquareRoot I could probably snap ya a few pictures of it if you think that would be helpful, both to give you a visual on cat location and the shield.
 

Rusty Nail

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What about third gen f bodies?

They got them dual outlet mufflers - I bought a 50 series Flowmaster. :shrug:
Hope this helps!
 

SquareRoot

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Yea, that's a good point my truck has one. @SquareRoot I could probably snap ya a few pictures of it if you think that would be helpful, both to give you a visual on cat location and the shield.
That would be helpful. Thanks.
 

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