Single exhaust and cats

[C.I.Blazer]

Getting so close to starting up I can't stand it! I am waiting for my radiator to arrive and thought while I had a break I would tow the truck up to the exhaust shop and get that done.

My goal with the truck (6.0 swap into a 1971 Blazer) is to have a good solid daily driver. This will be my primary driver although I have a work vehicle and we generally take my wife's car when we go out together so it will not get a ton of miles. I am not worried about a ton of horsepower; I think the upgrade to the LS will be plenty. I do not car about the sound. In fact quite the opposite, I want to it to be quiet and comfortable to drive around.

Local shop recommended I go with a stock-ish system with a Y-Pipe into a single 3" exhaust. They also recommended keeping the Catalytic converters for cleaner burning and reduced gas smell. I still have the cats from the donor so thinking about using those if they are in good shape.

Anyone go with a Y-pipe and single exhaust? Anyone keep their cats? I am using a PSI harness and will not have rear 02 sensors. The PCM has already been programmed to delete them. Does that matter? I know they are used to determine if the cats are working efficiently. Can I run cats without them?

Thanks for the help!

[AussieinNC]

In simple terms, yes, you can run the cats / cat without downstream sampling data going to the ECM...(assuming it was correctly updated)

A single 3" system is fine for a street daily driver...there are millions of similar systems out there on daily drovers.

A single pipe system is also easier to install and maintain. Just ensure the muffler is an easily replaceable unit, not a custom build.

Hope this helps

[LS short box]

On my Jeep TJ LS6 swap I'm running 3" single exhaust. On my 68 C10 LS swap I'm 3" from the headers duals reduced to 2.5". If you go single exhaust I would go 3".
On the Jeep it has 20" long turbo muffler 3" in and out. Pretty mellow sound. Use a good 2 into 1 merge like a flowmaster. Don't tee one pipe into the other.
Nothing against muffler shops but if they have the typical pipe bender when they make 90 degree bends it really crushes the pipe. Kind of like when they bring the one side of the exhaust over to meet the other and over the axle.
I like to build my exhaust out of mandrel bend pieces and straight pipe. No crushed bends. Kind of tedious work I think its worth it.
I wouldn't bother with the cats. I don't have any gas smell with no cats. I think you can get a few bucks for the stock cats.

[LeesTruk]

Back in 2015, when I put my truck together('80 C10, 5.3L/4L60E), I made a y-pipe for it, using mandrel bend kits that are available. Piping from the flanges is 2 1/2" into a 3" Y collector, then into a 3" exhaust pipe. For a muffler, I, too, didn't want an obnoxiously loud piece, so I chose a Walker QuietFlow SS unit, with a 3" tailpipe exiting behind the right rear tire, pretty much in a stock location. Sounds pretty good, without being overly loud

[LS short box]

Just another suggestion. Don't use the typical muffler clamps. When you tighten them they crimp the exhaust tubes and make it very difficult to take apart in the future if you have to. Use the single bolt band clamps to clamp the sections together just like they do on new cars and trucks.

[C.I.Blazer]

Thanks for the input! Interestingly enough I just saw an episode of Engine Masters that compared dual to single exhaust. I have decided to go with the 3" single and will ensure they combine them using a "Y" and not a "T". Thanks for the suggestion.

They are going to build the entire thing with V-Band clamps so it should be easily removable. The truck is very much a work in progress so I will need to take the exhaust out and do A LOT more work over time.

Still need to decide on the cats. Glad to hear I can use them without the second set of O2 sensors. I always believe that simpler is better and like the idea of fewer parts that can go wrong. I need to balance that with making sure I do not have a lot of gas smell which my wife would not like. Anyone else have input on keeping or getting rid of the cats?

[kipps]

I'm definitely interested in this. My goals for my build are identical to yours. A solid daily driver, quiet exhaust, and simple maintenance. I also would like to keep the cats. I've done a little preliminary mock-up, and they're a very tight fit in the stock location. I think it's doable, but there's definitely less room on these trucks than there is on the newer GM donors.

I had hopes of using the stock muffler from the donor, but that thing is huge! I'm not sure I'll be able to get it to fit between the driveshaft and the framerail.

I was not aware of the t-pipe vs y-pipe difference on a single exhaust. I'll keep that in mind.

Where are you expecting to install v-bands? I was thinking of installing one immediately after the two pipes merge into one. Are there other places you'd install them?

[MalibuSSwagon]

I did the same, single 3" exhaust, used a big magnaflow tho, it sounds good but isn't obnoxiously loud.

I'd just sell the cats and go without them. With a stock EFI setup and tune, there's no perceptible exhaust smell like an old carb'd engine would have. Besides those 6.0L cats are worth good money and reselling them to a recycler would pay for your new exhaust.

[LS short box]

So in my post I wasn't suggesting v-band clamps. What I like are the single bolt band clamps that are about 1" wide. I worked as a line tech at a chev dealership many many years ago and we had a tubing bender. When we were trained on exhaust systems we taught to expand the down stream piece of tube so the upstream tube slides into the down stream tube or muffler. The reason for this the exhaust can't leak unless a really bad fit.
When you start building the exhaust make small cuts around the radius of the tube so the band clamp can compress the tube. Also a bit of muffler cement will make sure there are no leaks but you can still take it apart if needed.
Again I don't see the point of the cats if you have good tune.
Just my.02.

[C.I.Blazer]

Thanks for the additional info. Not exactly sure yet on how to clamp the thing together. I spoke with the shop that will be doing the work and just told them I need to be able to relatively easily remove the system to work on the truck. The shop specializes in a lot of restorations and he said he did this all the time. I will figure out the details when I drop it off and talk with him face to face.

The shop came highly recommended from a local builder I know that does a lot of high end builds. I had a really great feel about them when I spoke to them. He spent a lot of time just asking what my goals were and recommending the single exhaust based on them even though they would make more money off a dual setup. Also, he has a '72 K10 that he is starting a swap on so that was cool too.

I confirmed with PSI that I can run cats if I want to with no rear O2 sensors without a problem. Still not sure which way I want to go on that one.

[Rich84]

You are more likely to smell gas vapor from the tank then you are from the exhaust.

[kipps]

Originally Posted by C.I.Blazer

I confirmed with PSI that I can run cats if I want to with no rear O2 sensors without a problem. Still not sure which way I want to go on that one.

Your truck is old enough to be completely pre-emissions. Mine is a 87, so I intend to run cats(or cat look-alikes) to more easily pass the Virginia safety and emissions(visual only) inspection.

[biketopia]

functioning cats will knock down any chance of a fuel odor. Having no cats and a fairly aggressive cam can really make it more pronounced at idle. If you're a stock engine, it won't be terrible, but if you have em and the shop can put them in for you, it certainly won't hurt anything. It will also help to keep the truck quiet. Hallowed out cats can actually make your exhaust a lot louder as they act like an expansion chamber.