Exhaust flapper vales

[asalinasz39]

So I noticed my AT4 has two valves one before the muffler and one after the muffler. Has anybody clamped them open as it was done in the previous gen?

Just looking into getting a bit more sound. I went under the truck and held one open but didnt notice much difference. Today I stumbled upon a youtube video and noticed their was two valves. I guess I can give it a go this weekend; basically just wondering if its been done and if you are happy with the results.

[BLACK AT4]

7 minutes ago, asalinasz39 said:

So I noticed my AT4 has two valves one before the muffler and one after the muffler. Has anybody clamped them open as it was done in the previous gen?

Just looking into getting a bit more sound. I went under the truck and held one open but didnt notice much difference. Today I stumbled upon a youtube video and noticed their was two valves. I guess I can give it a go this weekend; basically just wondering if its been done and if you are happy with the results.

Yes, i removed both valves. They each have a 1.25" restriction. The aftermarket GM (Borla) exhaust eliminates the valves. I cut both mine off and installed a Magnaflow 12909 and gave it the sound and performance it should have.  attached is a picture of the valve in the open position.

[asalinasz39]

26 minutes ago, BLACK AT4 said:

Yes, i removed both valves. They each have a 1.25" restriction. The aftermarket GM (Borla) exhaust eliminates the valves. I cut both mine off and installed a Magnaflow 12909 and gave it the sound and performance it should have.  attached is a picture of the valve in the open position.

Interesting to know. I was under the impression that the halve would open fully. 

[BLACK AT4]

1 minute ago, asalinasz39 said:

Interesting to know. I was under the impression that the halve would open fully. 

If that half round section wasn't part of the valve, it would be fine, however, i'm sure it's part of the reason its sounds the way it does. 

[gothp28]

This is interesting. I wonder if the back pressure somehow creates more horse power?

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[destrada127]

This is interesting. I wonder if the back pressure somehow creates more horse power?

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Back pressure assists with the cats working properly but does not help performance

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[asalinasz39]

I found this which would be easy to install but the price is just too exaggerated I think; plus the valves would still remain in place as it does not state that it's long enough to cut them off. Perhaps I am wrong.

 

Edited March 29, 2019 by asalinasz39

[GymC]

22 minutes ago, asalinasz39 said:

I found this which would be easy to install but the price is just too exaggerated I think; plus the valves would still remain in place as it does not state that it's long enough to cut them off. Perhaps I am wrong.

 

The GM exhaust kit does away with the flappers, there is no reason to keep them. It's cheaper and more effective to just cut the flappers off and install a Magnaflow or similar muffler and be done. A muffler shop can do it all in less than an hour. It's easy stuff for them. 

[GymC]

1 hour ago, gothp28 said:

This is interesting. I wonder if the back pressure somehow creates more horse power?

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The GM aftermarket cat back system does not use the flapper valves. That tells me they don't aid in horsepower, rather they restrict it. 

[snowman44]

So I am looking at this muffler Borla XR-1 Racing Mufflers 40085 or the carven r which I loved on my 2016.  WHen they put in aftermarket muffler what do I tell muffler shop to do eliminate the flapper valves or do they get eliminated when you put in aftermarket exhaust.  SOrry if this is a stupid question just want to give shop the right directions.

[asalinasz39]

2 minutes ago, GymC said:

The GM exhaust kit does away with the flappers, there is no reason to keep them. It's cheaper and more effective to just cut the flappers off and install a Magnaflow or similar muffler and be done. A muffler shop can do it all in less than an hour. It's easy stuff for them. 

 

1 minute ago, GymC said:

The GM aftermarket cat back system does not use the flapper valves. That tells me they don't aid in horsepower, rather they restrict it. 

Totally makes sense to me guys! Thanks! I will temporary clamp the valves open and see what it sounds like until I have a chance to head out to the muffler shop and cut them off followed by a replacement muffler.

[asalinasz39]

1 minute ago, snowman44 said:

So I am looking at this muffler Borla XR-1 Racing Mufflers 40085 or the carven r which I loved on my 2016.  WHen they put in aftermarket muffler what do I tell muffler shop to do eliminate the flapper valves or do they get eliminated when you put in aftermarket exhaust.  SOrry if this is a stupid question just want to give shop the right directions.

You should tell them to eliminate them just to make sure they do and get your full performance and sound desired. 

[GymC]

1 minute ago, asalinasz39 said:

 

Totally makes sense to me guys! Thanks! I will temporary clamp the valves open and see what it sounds like until I have a chance to head out to the muffler shop and cut them off followed by a replacement muffler.

That won't help much.; They have a 1.25" restriction (as per the photo above) when open. Best to cut them off. 

[GymC]

4 minutes ago, snowman44 said:

So I am looking at this muffler Borla XR-1 Racing Mufflers 40085 or the carven r which I loved on my 2016.  WHen they put in aftermarket muffler what do I tell muffler shop to do eliminate the flapper valves or do they get eliminated when you put in aftermarket exhaust.  SOrry if this is a stupid question just want to give shop the right directions.

Not a stupid question at all. When they install the aftermarket muffler they can either cut off the valve and hand it to you so it can be reinstalled later if need be, or they can leave it. They are located behind and in front of the OE muffler (if you have a 6.2). I doubt there would be much of a performance difference if you leave them, however it will be quieter due to the restriction. I say cut them off, weld on the new muffler, give it a chance to break in and see if you like it. If it's too much, they can weld one back in. If it's still too much, weld in the other one. I would leave the resonators, they are straight through and don't offer any performance advantage if you cut them off. 

[asalinasz39]

So i was under the impression that my AT4 had 2 valves however looking under the truck mine only has 1. I had seend a youtube video earlier with a 6.2 At4 and that must of thrown me off. My 5.3 only has 1 valve.


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