Semi dual exhaust

TrueBlue · March 26, 2025

I had a Magnaflow 14" muffler on it, dumping out behind rear passenger tire. Wanted a bit more sound and a better look. Muffler guy told me if he ran true dual exhaust from the cat back it would likely void my warranty because GM doesn't want to have to deal with a welded connection there. So I had him install a dual outlet Magnaflow, 14" again, and then route the two pipes under the back bumper. I like the sound, though I'm hoping the very slight drone I'm hearing at certain pedal positions does not get any louder at the muffler packing loosens. With the other I had zero drone. This tone is louder and deeper and I like it a lot, just so long as it stays quiet in the cab at cruising speeds. Love the look though regardless.

Transient · March 27, 2025

Muffler guy is an idiot. Look up Magnuson-Moss Warranty Act. Regardless, what matters most is how satisfied you are with it. It doesn't matter what anybody else thinks or says. With that said, I think your setup looks good.

Edited March 27, 2025 by Transient

KARNUT · March 27, 2025

At least in the last 10 years probably longer. Exhaust restriction was minimal from the factory. I’ve gone with the setup in the picture above one in two out. After seeing a test on TV with different exhaust on stock vehicles. Those results were a single large pipe after the muffler was slightly less restrictive. My last exhaust on a truck was a less restrictive muffler and one pipe straight out the back. I always had one exhaust shop. All exhaust work was custom. The only time I can remember not having some kind of drone. Was during the pre cat days. Exhaust was very restricted stock and 21/4 inch duals and no cross over was the norm. At the same time the cruising RPM was higher with only 1 to 1 final ratio. Usually with later vehicles with over drive and tuned exhaust. I would leave them in drive or a gear lower in town. Shifting into overdrive only on the highway canceling drone.

TrueBlue · March 27, 2025

He's owned his shop there for about 30 years. If we had gone with what I wanted it would have been two mufflers in back of a Y pipe. What he installed was a single, dual outlet muffler, no Y pipe. This was less expensive than what it would have been. I've used this guy for years myself and I've never gotten the impression he was talking out of his hat.

The Magnusson Act allows for customers/owners to work on their own vehicles, and to prevent unfair voiding of warranty by manufacturers. But it doesn't prevent that from happening in every case. What the guy was saying is that if the exhaust couldn't be unbolted from the truck in order to do warranty work, the dealership would have to cut it off and then have it rebuilt/repaired by a third party when putting it back together. And thereby giving them the opportunity to refuse to fix it under warranty. I have no idea if that would be the case but, not wanting to chance it I decided to go with his recommendation given that I simply wanted a certain sound and look. Which I got.

KARNUT · March 27, 2025

33 minutes ago, TrueBlue said:

He's owned his shop there for about 30 years. If we had gone with what I wanted it would have been two mufflers in back of a Y pipe. What he installed was a single, dual outlet muffler, no Y pipe. This was less expensive than what it would have been. I've used this guy for years myself and I've never gotten the impression he was talking out of his hat.

The Magnusson Act allows for customers/owners to work on their own vehicles, and to prevent unfair voiding of warranty by manufacturers. But it doesn't prevent that from happening in every case. What the guy was saying is that if the exhaust couldn't be unbolted from the truck in order to do warranty work, the dealership would have to cut it off and then have it rebuilt/repaired by a third party when putting it back together. And thereby giving them the opportunity to refuse to fix it under warranty. I have no idea if that would be the case but, not wanting to chance it I decided to go with his recommendation given that I simply wanted a certain sound and look. Which I got.

Best way to go. Especially since the second muffler would have added restriction.

Transient · March 28, 2025

12 hours ago, TrueBlue said:

He's owned his shop there for about 30 years. If we had gone with what I wanted it would have been two mufflers in back of a Y pipe. What he installed was a single, dual outlet muffler, no Y pipe. This was less expensive than what it would have been. I've used this guy for years myself and I've never gotten the impression he was talking out of his hat.

The Magnusson Act allows for customers/owners to work on their own vehicles, and to prevent unfair voiding of warranty by manufacturers. But it doesn't prevent that from happening in every case. What the guy was saying is that if the exhaust couldn't be unbolted from the truck in order to do warranty work, the dealership would have to cut it off and then have it rebuilt/repaired by a third party when putting it back together. And thereby giving them the opportunity to refuse to fix it under warranty. I have no idea if that would be the case but, not wanting to chance it I decided to go with his recommendation given that I simply wanted a certain sound and look. Which I got.

I could shed that apart, but it's pointless. You and I are likely not going to see eye to eye on this. I simply disagree with your trusted short term shop owner. 12 years is not a very long time, but at least he's beaten the majority of the business odds against him. Congrats to him on that. What you claim he's telling you doesn't make a bit of sense, imo. It's your money and your truck. Do with both as you wish. As I said earlier, the result looks good. Glad to hear you're happy with it.

Silverado4x4 · March 28, 2025

I believe what TrueBlue is saying about his muffler guy. A few years ago I was at the dealership and someone came in to have warranty work done to their car the service dept would not do it due to the person had a sub woofer box install in the back of the car and the box would have to be un-bolted and unhooked to do the warranty work. So his muffler guy is right.

Bikerjon · March 28, 2025

23 hours ago, TrueBlue said:

He's owned his shop there for about 30 years. If we had gone with what I wanted it would have been two mufflers in back of a Y pipe. What he installed was a single, dual outlet muffler, no Y pipe. This was less expensive than what it would have been. I've used this guy for years myself and I've never gotten the impression he was talking out of his hat.

The Magnusson Act allows for customers/owners to work on their own vehicles, and to prevent unfair voiding of warranty by manufacturers. But it doesn't prevent that from happening in every case. What the guy was saying is that if the exhaust couldn't be unbolted from the truck in order to do warranty work, the dealership would have to cut it off and then have it rebuilt/repaired by a third party when putting it back together. And thereby giving them the opportunity to refuse to fix it under warranty. I have no idea if that would be the case but, not wanting to chance it I decided to go with his recommendation given that I simply wanted a certain sound and look. Which I got.

I think the round duals out the back look great. On my last truck 2023 Trail Boss I had my muffler guy install a high flow glass pack and cut out the flapper. I started noticing some stuttering from the transmission at low rpm under heavy acceleration. After taking it to the dealer the tranny guy blamed the missing flapper valve! You just cant be too careful.

KARNUT · March 28, 2025

16 minutes ago, Bikerjon said:

I think the round duals out the back look great. On my last truck 2023 Trail Boss I had my muffler guy install a high flow glass pack and cut out the flapper. I started noticing some stuttering from the transmission at low rpm under heavy acceleration. After taking it to the dealer the tranny guy blamed the missing flapper valve! You just cant be too careful.

In the mid 2000s we had three 5.9 Cummins Rams. They had a run of over fueling filling the crank case with diesel. All ours were affected. The higher mileage one before we knew of the problem had an engine failure. It was at night the engine light came on but it was too late. Still under warranty. They denied because it had a banks manifold. Even though it was an injection problem. Nothing to do with air. It was fuel. Could we have fought it, we needed the truck. We did a reman. The other two we put in after market injectors.

Edited March 28, 2025 by KARNUT

TrueBlue · March 28, 2025

25 minutes ago, Bikerjon said:

I think the round duals out the back look great. On my last truck 2023 Trail Boss I had my muffler guy install a high flow glass pack and cut out the flapper. I started noticing some stuttering from the transmission at low rpm under heavy acceleration. After taking it to the dealer the tranny guy blamed the missing flapper valve! You just cant be too careful.

Thanks Jon. Me too

I had the flapper removed when I had the first exhaust installed. I've been watching the reports of tranny shuddering closely. So far so good, for me. I'm kind of at a loss to understand how it could be related to an exhaust component, but, I'm not an engineer or even a GM certified technician.

Edited March 28, 2025 by TrueBlue

Bikerjon · March 29, 2025

9 hours ago, TrueBlue said:

Thanks Jon. Me too

I had the flapper removed when I had the first exhaust installed. I've been watching the reports of tranny shuddering closely. So far so good, for me. I'm kind of at a loss to understand how it could be related to an exhaust component, but, I'm not an engineer or even a GM certified technician.

I've been a mechanic and Fleet Manager for over 35 years. Transmission shuddering has nothing to do with exhaust. That was just a chicken sh*t excuse by the dealership to get out of a transmission diagnosis/repair.

TrueBlue · March 29, 2025

One would think they would welcome warranty repair. Though I'd guess they don't always come without a fight with the mothership over taking it on.

Transient · April 4, 2025

On 3/28/2025 at 7:31 PM, Bikerjon said:

I've been a mechanic and Fleet Manager for over 35 years. Transmission shuddering has nothing to do with exhaust. That was just a chicken sh*t excuse by the dealership to get out of a transmission diagnosis/repair.

Beat me to it. I'd love to see GM deny warranty work for a missing flapper on a vehicle with the GM Performance exhaust. Iirc, the exhaust isn't stamped or marked "GM Performance." The muffler has Borla stamped on it. It's the exact same kit sold by Borla as their touring or sport exhaust. Whichever is quieter. Anyways, the flapper gets removed to install the cat back exhaust sold by GM. I know because I have it, and installed it (it's been almost 5 years). The exhaust even carries its own warranty of 12 months/12,000 miles with GM, unless it's installed by a dealer tech prior to the customer taking possession of the vehicle brand new. At that point the applicable vehicle warranty/warranties apply. Missing flappers are a garbage excuse. It's just the dealer BSing you and assuming you won't push back. Demand letters from a lawyer is cheap. It's the litigating that gets expensive. Most dealers won't go any further once a lawyer writes a letter.

Edited April 4, 2025 by Transient