5"exhaust and muffler

[The Inventor]

Changed out part of the exhaust pipe and muffler this weekend. Have 03 HO. The exhaust pipe looked like 3" and the tailpipe is 4". Had a buddy weld up the system, he positioned the muffler far forward he said to reduce sound emissions. Configuration: stock 3” down pipe, 5" muffler installed just after the bend, 5' of 5" pipe to 4" tail pipe. The muffler is a straight thru with louvers that I bought from City Muffler for $75. The 5" pipe and reducers are avail from NAPPA $9/ft. $20ea. It was an easy straight-line hookup not affected by the stock offset. It definitely breaths allot better but the thing is too loud on acceleration and has a low-end drone on hwy. Engineering tradeoff reduce sound in the cab vs backpressure and EGT. My questions:



Can a 5' pipe be hooked up to the manifold? (it looks like a 3" manifold opening)

Will changing the short 3”pipe (manifold to bend) have much difference in back pressure and EGT? How will this affect future installation of an exhaust brake?



Does the position of the muffler (forward or rearward) affect the noise in the cab?



What can be done to reduce noise in the cab? Adding a 2nd straight thru muffler? Adding a resonator? Different muffler?



This is my 2nd CTD

03 3500, 4Dr LB, 2WD, SLT Laramie, HO, 6Spd, Prodigy brake controller, Gooseneck, ... soon to be Edge, AFE



1st CTD stock 94 SLT Laramie, LB, POS Automatic

 

[Forrest Nearing]

a 4" downpipe (attatched to the back of the turbo) will help spool the turbo up quicker and reduce EGT's



the best thing for reducing interior resonance is to line the interior sheet metal with sound deadener.



I've done a lot of tinkering with different exhaust configurations and tricks to reduce interior resonance, and the #1 biggest thing is sound deadener.



I'm at the point now where the only resonance point on my truck is the actual downpipe itself. I'm currently running 5" straight pipe. just today I took off an 11" resonator and an 8" resonator, and the interior resonance is exactly the same w/ the straight pipe, possibly slightly LESS because I added some mass to the long stretch of 5" pipe (piece of angle iron along the top of most of it, a 1" wide strap of 1/8" steel welded/heated/wrapped around the bottom, and a 5lb weight welded to the top of the pipe at the very front of the pipe where it meets the flex pipe going to the downpipe) , but the resonance coming from the firewall area is the same between the two systems, and the straight pipe is a LOT louder outside the truck than the two resonators were!



next project will be adding mass to the downpipe!



another thing to consider, how did you install the muffler? are the louvers facing forward or back? that will make a difference.



anyhow, you can put huge mufflers on it, and they will help, but the greatest difference will come from sound deadener... and it is one area where more is pretty much always better!



Forrest

 

[jsimpson]

The back wall of the cab is a huge sounding board. Use a quality sound insulation there and gain huge benefits. Insulation in the doors also helps a lot but is difficult to install.

 

[The Inventor]

When I bought the truck I had Mass Loaded Vinyl (MLV) wrapped around the interior of the truck. It was installed on the interior floor, back of cab, and in the doors. MLV is used extensively in sound deadening, is very heavy, and probably added 300lb to the vehicle. Sounds like (no pun intended) the same principle Forrest used adding mass to the pipe. The MLV has made a difference, it is quieter inside. I will have my welder weld some angle iron to the pipe. The muffler was installed as per the stamping on the muffler inlet connected to inlet (louvers facing rearward). A rep from Borla recommended installing the muffler with the louvers facing forward to provide more sound deadening.

I am considering undercoating the outside back wall, bottom of the cab and firewall. Also considering wrapping the muffler with high temperature ceramic fiber insulation.





03 3500, 4Dr LB, 2WD, SLT Laramie, HO, 6Spd, Prodigy brake controller, Gooseneck, ... soon to be Edge, AFE. I KNOW He does!

 

[Forrest Nearing]

yeah, that's odd, because the muffler that came w/ my 5" City Muffler kit listed the Inlet as the side that saw the open part of the louvers...



another thing... if you rap the case of that muffler w/ your knuckle, you'll probably hear a pretty good ringing... I'd weld some angle or strap to it to keep the case from resonating as much too.



Forrest