What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[iamdub]

iamdub beat me to it...sort of. The term for what's in that photo is a quarter-wave attenuator, which is a specific type of Helmholtz chamber tuned to damp sound at a specific frequency. You have to know the engine RPM where you want the damping to occur. And you calculate the length of the pipe based on the "time of flight" of a pressure pulse down and back to the mouth of the attenuator. The goal is for a peak to arrive as a valley passes by in the main tube, and vice versa. I installed a set on my Mustang Cobra after I put Flowmasters on, and was getting a pretty severe drone at 2500rpm...right at cruising speed with my 3.73 gears.

View attachment 230103

They reduced the sound by 4dB, according to the sound meter app on my phone, which is more than half attenuation. They have to be tuned for a single frequency though. If you're getting drone at a wide range, this won't completely resolve the issue. Also, remember that the density of the exhaust gasses varies pretty dramatically with temperature. So you have to guess (or measure) an exhaust gas temperature for best results.

***EDIT*** I mis-remembered it was 4dB not 8 (corrected).

Easy now! You don't wanna scare him off with the deep 'n' nerdy stuff right off the bat. You gotta test the waters first. I think @R3cord303 is game, though.

Beautiful pipe work on that 'Stang.

 

[Doubeleive]

Well I don't know what temp cat's are normally or what they should be but the thermometer says anywhere from 300-400 depending on where I pointed it, tech2 says 3way is 775 on each, what about these long term fuel trims?

 

[R3cord303]

Easy now! You don't wanna scare him off with the deep 'n' nerdy stuff right off the bat. You gotta test the waters first. I think @R3cord303 is game, though.

Beautiful pipe work on that 'Stang.

Will add it into the design. At some point i’ll actually do the math and figure out tubing diameter, cfm, what to do for size/length of these chamber doodads

 

[kbuskill]

Will add it into the design. At some point i’ll actually do the math and figure out tubing diameter, cfm, what to do for size/length of these chamber doodads

Here is something to get you started...



Hope it helps.

PS... most people think they need bigger pipe than what is actually necessary.

 

[gooffeyguy]

Well damn, my 600hp mustang only has a 2.5" dual exhaust system.

Maybe I'll get 20 more hp if I up it to 3", 50 more hp if it's painted red

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

 

[07Burb]

Well damn, my 600hp mustang only has a 2.5" dual exhaust system.

Maybe I'll get 20 more hp if I up it to 3", 50 more hp if it's painted red

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

and don't even talk about if you added neon to the underside

 

[mikeyss]

Don't forget, you need this too!

 

[Doubeleive]

well from what I have read the cat temps seem to be pretty normal, on the freeway they ran in the 1500's both of them dead even same temp no matter what it was, fuel trims seem to be normal, all 4 02 sensors seem to be normal also, so i'm stumped.

 

[kbuskill]

well from what I have read the cat temps seem to be pretty normal, on the freeway they ran in the 1500's both of them dead even same temp no matter what it was, fuel trims seem to be normal, all 4 02 sensors seem to be normal also, so i'm stumped.

Perhaps you have gained weight in your right foot.

 

[wjburken]

well from what I have read the cat temps seem to be pretty normal, on the freeway they ran in the 1500's both of them dead even same temp no matter what it was, fuel trims seem to be normal, all 4 02 sensors seem to be normal also, so i'm stumped.

I know it’s a dumb question but have you checked the dashboard estimated mpg with the manual method of fill tank, drive, refill tank and do the math?