Installed Borla/GM cat-back Exhaust System

jimlem · January 23, 2015

Other than sound, any noticeable performance gains?

I can't give you dyno numbers but as I mentioned above, Borla hints at a 3%-5% HP gain. This works out to between 10 and 17 HP on my 5.3L. I can tell you that from a "seat of the pants" feeling, it does seem to stretch out each gear and it "feels" faster. Probably that's mostly due to the better sound. But then again, isn't that why most of us buy these?

Roader · January 23, 2015

The 10-17hp is not at the wheels. He will be able to hear the difference between this and stock but not feel a difference

jimlem · January 23, 2015

The 10-17hp is not at the wheels. He will be able to hear the difference between this and stock but not feel a difference

Yeah. Like I said, the true enjoyment is the sound. You'd need a full on custom exhaust with headers and at least a good CAI to really make some usable power.

jimlem · January 24, 2015

I also went with the GM Borla Exhaust. Even though Borla won't confirm that the GM system uses their "Touring" muffler, that's probably what it is. They claim the muffler in the GM Borla system is "to GM Specifications" but probably is the regular Borla "Touring" model.

I am very happy with the system. For some, it might be a little on the tame side, but for me, it's just perfect. One thing you have to remember is that with the cabs of the new trucks being so quiet, the exhaust sound outside is quite a bit louder than you would think. I had my son drive my truck and I stood outside so I could hear the exhaust, and I was quite surprised as to how much sound there actually is. You wouldn't know I had a "performance exhaust" on the truck from the inside, until you get on the go pedal. Then it's a nice rumble as the RPM's increase. I have no drone at all, and no problem with the V4 "flutter / helicopter sound" etc. It's a perfect sound for me, a fair bit louder than "Stock" but not at all raspy or offensive.

The GM Borla system has an integrated adaptive exhaust valve, where as a system purchased directly through Borla, even though one for a GM truck, will not have this valve. It must be this valve that controls all the unwanted drone etc. The system is pricey, but it works. I was apprehensive when I first decided to go this way, as the price was similar to the OP's, but after having had the system on now for about 3 months, I don't regret the cost. The system gives me the sound I want, without any of the usual annoyances that are present with a lot of the other systems out there.

REV

A few pics of the GM Borla System, and the Borla adaptive valve, included with the system

REV thanks for the pics. I wanted to call attention to your second photo. If you guys look at it you'll see it's the same valve as GM's stock flapper valve. I compared the two side by side and they are the same valve. However, on the Borlas, you see a 1" diameter "C" shaped bypass pipe that circumvents the entire flapper valve. It's open all the time. Anyone have an idea why Borla added this and why GM does not use it? Also on the OEM exhaust the entire flapper valve system is down stream from the muffler but Borla's system the flapper and bypass pipe are before the muffler, right behind the 3rd cat. Anyone have any ideas on these differences?

seansharley · January 24, 2015

i would assume the bypass makes up for the restricted size due to the flapper being inside the pipe

russ9443 · January 25, 2015

REV thanks for the pics. I wanted to call attention to your second photo. If you guys look at it you'll see it's the same valve as GM's stock flapper valve. I compared the two side by side and they are the same valve. However, on the Borlas, you see a 1" diameter "C" shaped bypass pipe that circumvents the entire flapper valve. It's open all the time. Anyone have an idea why Borla added this and why GM does not use it? Also on the OEM exhaust the entire flapper valve system is down stream from the muffler but Borla's system the flapper and bypass pipe are before the muffler, right behind the 3rd cat. Anyone have any ideas on these differences?

Are you sure it's a 1in bypass?

They most likely put it up stream so they could run duals out the back.

I did a custom exhaust with the bypass down stream of the muffler and a 14in magnaflow. I think my bypass is 1.5 or 1.75in. Maybe I will have it changed.

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jimlem · January 25, 2015

Are you sure it's a 1in bypass?

They most likely put it up stream so they could run duals out the back.

I did a custom exhaust with the bypass down stream of the muffler and a 14in magnaflow. I think my bypass is 1.5 or 1.75in. Maybe I will have it changed.

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Russ - It appeared to me to be about a 1" dia. pipe but I did not measure it. I can say for sure after seeing your pic that it was NOWHERE NEAR THAT BIG! As a matter of fact, Borla is real keen on smaller tubing as they say it works well in certain of their setups and helps to make the sound everyone likes. All the pipes in your photo look bigger than Borla's. Also, what exactly is the bypass for? Can you explain?

SILVER SLED · January 25, 2015

I work at a Chevy dealership, and we installed a borla for a customer. We started the truck with no cat back and we're amazed at how quiet the truck was. The y-pipe with its three cats is quiets the exhaust quite a bit. FYI, the customer had the loud flapper syndrome so we allowed him to pay the diff between a stock exh and the borla, about $600.

russ9443 · January 25, 2015

Russ - It appeared to me to be about a 1" dia. pipe but I did not measure it. I can say for sure after seeing your pic that it was NOWHERE NEAR THAT BIG! As a matter of fact, Borla is real keen on smaller tubing as they say it works well in certain of their setups and helps to make the sound everyone likes. All the pipes in your photo look bigger than Borla's. Also, what exactly is the bypass for? Can you explain?

My exhaust is 3in. Thought that is what borla used too. That photo might be making it look bigger than it is.

My guess on what it does it help negate some of the restriction of the valve, it seems to allow a bit more sound through, like at idle, and if your valve freezes shut I bet you could still start the truck.

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SILVER SLED · January 25, 2015

One diff between the borla and a stock exhaust is that the flapper on a stock exhaust does not completely block off exhaust pipe, where as the borla flapper does or almost does completely block off tubing. Hence probably why the bypass tube. For whatever reason.

jimlem · January 26, 2015

One diff between the borla and a stock exhaust is that the flapper on a stock exhaust does not completely block off exhaust pipe, where as the borla flapper does or almost does completely block off tubing. Hence probably why the bypass tube. For whatever reason.

When you look inside the pipe at Borla's flapper, you see it's not quite big enough around to block off the pipe. There's a few mm gap all around. Also the Borla flapper has an approx. 1/2" hole drilled thru the center of that flapper valve. I agree with you on the bypass tube. I bet if you factor in the flow of the gap around the flapper, its center hole and the flow of the bypass pipe, it probably all adds up to just enough flow to make good sound in V4 mode. That's just my guess.

Shimmy Bang Bang · January 26, 2015

I would love to watch a video of the GM Borla exhaust. I am considering this product.

russ9443 · January 27, 2015

When you look inside the pipe at Borla's flapper, you see it's not quite big enough around to block off the pipe. There's a few mm gap all around. Also the Borla flapper has an approx. 1/2" hole drilled thru the center of that flapper valve. I agree with you on the bypass tube. I bet if you factor in the flow of the gap around the flapper, its center hole and the flow of the bypass pipe, it probably all adds up to just enough flow to make good sound in V4 mode. That's just my guess.

The "borla" flapper is actually just the one from the 6.2 stock muffler. It's 3in. I noticed the differences you guys pointed out when they put mine together. The shop I use had a stock 6.2 valve for me to use.

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revitupfaster · January 27, 2015

I would love to watch a video of the GM Borla exhaust. I am considering this product.

There isn't any video that will give you a true representation of the GM Borla exhaust. You have to experience it, inside the truck. There is a sound clip on You tube where they have a Burgundy 2014 Silverado with the GM Borla system on it, but even this "Professionally" done clip doesn't give what I would call an accurate representation.

I was lucky, as my dealer always keeps a truck already set up with the Borla system. He says it's a good selling feature once a potential buyer hears it. Anyway, I was able to go for a short ride, and hear the thing myself. I really don't think that can be duplicated with a computer sound clip.

I would ask your dealer if any of his customers have installed the GM Borla system. I'm sure if there are any, they would be happy to talk to you about it, and give you a first hand demo, and the dealer may just sell another system.

Good luck

REV

revitupfaster · January 27, 2015

Are you sure it's a 1in bypass?

They most likely put it up stream so they could run duals out the back.

I did a custom exhaust with the bypass down stream of the muffler and a 14in magnaflow. I think my bypass is 1.5 or 1.75in. Maybe I will have it changed.

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Russ.......how does your system sound. Do you have any V4 sound issues or droning? Looks pretty much like the GM Borla system except for the pipe sizes, where yours seem to be a little larger diameter. Mostly are you happy with it, after all, that's all that counts?

REV