Stock muffler flapper inside pic

[2018GMC]

I had my stock muffler and flapper chopped off and replaced with a flow through magnaflow 12909 / 14909. 

 

Heres some one pics of how restrictive the flapper is even wide open. 

 

This is off a 2018 GMC Sierra 6.2

 

 

[2018GMC]

[Rubyralph]

Looks like my 2014 exhaust valve, my 2017 has a round housing not the square design?

[tim5779]

Hows the drone at cruising speeds? I'm doing the same on my 18' 5.3, except leaving the flapper for now.  I've been told without it drone can be pretty annoying when it drops to V4

[Hillwood]

Someone should do before and after sound bites..

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[2018GMC]

There are some YouTube videos search magnaflow 22” or magnaflow 12909. 

 

No drone, even with v4. I do hear slightly louder v4 chop but I could always tell when it was in v4 stock due to different exhaust note. 

 

I have a range AFM disable for around town but use v4 on long highway trips. 

 

I would highly recommend magnaflow, delete flapper and keep resonator. 

 

It now sounds like a v8 above 2500 rpm and is still very quiet below that. 

 

I have towed with lots of time at 3.5K - 4.5k rpm and it sounds great! ? not too loud and still refined but with v8 growl. 

 

I can also hear cold starts while In The house. With stock muffler was always hard to tell.  

[2018GMC]

Magnaflow 

 

 

[2018GMC]

https://www.magnaflow.com/products?partNumber=12909

 

https://www.magnaflow.com/products?partNumber=14909

 

 

https://www.magnaflow.com/support/faqs/general-questions/whats-the-difference-between-stainless-steel-and-aluminized-steel/

 

 

[6.2_GMC_DEN]

On 12/30/2018 at 1:08 PM, 2009GMC said:

I had my stock muffler and flapper chopped off and replaced with a flow through magnaflow 12909 / 14909. 

 

Heres some one pics of how restrictive the flapper is even wide open. 

 

This is off a 2018 GMC Sierra 6.2

 

 

Definitely one of the best things I did on my truck!

[M1ck3y]

Are you keeping your stock muffler. Can you cut it open and post some pics?

[3tspapat]

The flapper opening is tiny! I have the GMPP Borla with flapper on it and is definitely at least 2x the size of the stocker flapper opening. Probably explains why I can hear some minimal chop while in V4. But once the wife and kids get into the truck all noises are drowned out