Bringing the Cat back...enough is enough.

[Joshua Keith]

I’m ignorant in when it comes to exhaust, but could you run no Y-pipe and dual cats?

 

[Grumpy]

Most emissions equipment creates more pollution than it prevents just through its own process of manufacture. Cats are filled with various rare metals, and it is the production of these metals where the biggest and longest lasting environmental impacts are created. The same goes for almost everything "green." There are already huge junkyards full of dead electric cars that now have been declared environmental wastelands.

Not to mention only one volcano erupts and pushed more CO2 and ash into the atmosphere in two days than most countries do in a year (China notwithstanding.)
If people truly are concerned about their own (miniscule) impact on the planet, they would walk everywhere naked and barefoot.

 

[84-C20]

That would be helpful. Thanks.

I've got the truck with me at work today so I'll get you some pics later on.

 

[SquareRoot]

Most emissions equipment creates more pollution than it prevents just through its own process of manufacture. Cats are filled with various rare metals, and it is the production of these metals where the biggest and longest lasting environmental impacts are created. The same goes for almost everything "green." There are already huge junkyards full of dead electric cars that now have been declared environmental wastelands.

Not to mention only one volcano erupts and pushed more CO2 and ash into the atmosphere in two days than most countries do in a year (China notwithstanding.)
If people truly are concerned about their own (miniscule) impact on the planet, they would walk everywhere naked and barefoot.

Tragedy of the commons.

 

[84-C20]

I’m ignorant in when it comes to exhaust, but could you run no Y-pipe and dual cats?

Yes you can do that, and if I had decided to go dual that's what I would have done, but there are a few down falls. One is cats are expensive and you'd need to buy two. The other issue is the longer it takes for the cat to get to operating temps the longer it takes for it to fully start working. Having two cats you'd be running half as much exhaust though them and it would take them longer to warm up.

Those are known facts, now this part is just my opinion, after having had rigs with dual exhaust and having had a few with larger pipe single exhaust I'm no longer interested in dual exhaust. I use to always run duals, until about 15 years ago when I bought a used class C motorhome it was a 77, on a Dodge chassis. I did a single large pipe exhaust on it and it was so much quieter inside on the highway when run for hours at a time, and the throttle and power felt just the same. At the shop I have seen where one side of a dual exhaust system for one reason or another does not flow as well as the other, and this could be as simple as one side has extra bends to get the exhaust around something. Anyhow because there is a flow difference some exhaust will continue to pass though the crossover in the intake manifold even after the engine is warmed up and the heat riser has opened. Because of this the engine will have trouble with perculation, and if bad enough overheating. Look I'm not saying running duals is a bad thing, but a large single system will accomplish the same thing for less money, less noise, and fewer potential problems IMO.

 

[Catbox]

I’m ignorant in when it comes to exhaust, but could you run no Y-pipe and dual cats?

Yes.
That is the way the exhaust under my truck is currently.
It passes the sniffer test just fine.

We are going to be redoing the dual 2-1/2 inch for a dual 3 inch system as we are big block and will be upping the power in the future.
I will have to buy two 3 inch cats, but we have to pass emissions where I live.

They do not have to cost hundreds of dollars, although they may not last 20 years.
I put one under my 1995 Suburban 18 years ago and only just replaced it.
So $100 for 18 years equates to a massive yearly cost of $5.56.

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[Bextreme04]

Honestly, I would just get basic stock replacement 2-1/2" cats... no need for high flow at your power output and with true duals. Put them right at the header outlets. Since you are running port fuel injection, make sure you have a intake with no heat crossover and you will have plenty of heat during the warm up cycle to heat the cats quickly right at the exit of the headers. This is how stock LS engines are done because it is far more efficient than trying to heat the cats through that long y-pipe. Especially if your headers are ceramic coated. If your EFI computer supports it, you can then have the primary O2 sensors in the header collector on each side and install a second one behind each cat for the EFI to monitor cat function and heating. I'm not sure if the aftermarket port injection supports those functions, but I know stock OBD2 ones(96-later) do.

I am running headers to dual 3" and dual flowmaster 50 series Big Block mufflers. The truck already had the mufflers on it when I bought it and I'm going to be going higher power Gen VI 454 in the future so I figured I would just build the exhaust for that. I will probably put cats in and add second O2 bungs after them when the big block goes in. The passenger side 3" currently goes up and over the crossmember next to my NP 205 and fits fine with plenty of clearance to everything. The big block 50 series mufflers are nice and quiet at highway speed but still throaty at idle and low speed.

 

[SquareRoot]

I don't have a lot of room underneath, at least towards the front. I have full length headers, a BIG cast iron NV4500 and a passenger side drop t-case to work around. I'm pretty sure a y-pipe is the way to go.

 

[84-C20]

I've got the truck with me at work today so I'll get you some pics later on.

@SquareRoot I'm sorry but things went sideways at work today and I did not get your pictures, but I will do so hopefully tomorrow.

 

[Dave M]

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.

 

[84-C20]

@SquareRoot In a moment I will upload some photos. These pics unfortunately are not of my truck, it's raining and I don't have a free lift to run it up on so this is of a customers rig, with 350 single exhaust. His is bone stock exhaust, but the components are in the exact same place right down to the cat mount, the only difference is his pipes are smaller. I have to upload from my phone and type much on that is hard for me.

 

[84-C20]

Hopefully this helps at least some

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[84-C20]

If nothing else it should give you a real good idea of where the cat should be located.

 

[Hunter79764]

I'll see if I can get a picture of mine tonight, I need to take a look myself. Mine is an 87 K20 'Burban with 350 and TH400, not sure how different it might be. I know mine is a massive pancake style pretty much right after the Y, and single 2.5" from the merge back I believe.

 

[Hunter79764]

I tried to get some pictures that showed it all, hopefully this might help a little?

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