Help me quiet down my truck please

[Danimal]

What is your engine displacement vs exhaust displacement? If you want quiet, you should target at least 10:1 ratio (If you've got a 6L motor, you want 60L exhaust)

That said, what you are describing is a resonance. Your exhaust is putting out a tone that your cabin loves to boom at. You've GOT to get rid of this either through a bigger muffler or different location of what you are running.

That, and you need to do some work to figure out how to get that exhaust further out either through the rear or out the side more. a 3" glass pack is NOT enough muffler.

Look at a Dynomax straight through to reduce back pressure but add volume.

[river1]

What is your engine displacement vs exhaust displacement?

what are you measuring to get exhaust displacement?

thanks jim

[Fat Cat]

What is your engine displacement vs exhaust displacement?

what are you measuring to get exhaust displacement?

thanks jim

The volume of the inside of the manifold, muffler and all exhaust pipe. 3" ID x 72" length would give you the pipe volume. Then you need to figure the volume of the muffler as well.

[river1]

pretty much as i figured, just never heard that phrase before.

thanks jim

[Danimal]

pretty much as i figured, just never heard that phrase before.

thanks jim

Most of the time you can ignore pipe diameter and focus on tuning volume but in your case, you don't seem to have much tuning volume so you'd better not ignore the pipes! I don't sweat exhaust manifolds usually.

Tone loves pipe. Putting bends in it only increases back pressure, doesn't do much for sound quality so I wouldn't believe putting a bunch of bends in it will do much. Any pipe that is long without a volume interruption is going to have a standing wave. The larger the diameter, the deeper the tone. Running 3" pipe on my son's stock 305 makes it sound like a big block. Y pipe to 3" (cat fell off) to a flow masher to a 2.75" pipe all the way out on an X cab 93 chevy. The best part is that it goes out the back. He's 16 and loves it. I'm 40 and know when he's coming or going.

Diesels don't like BP so you want the bigger pipe. The reason big trucks stack up in the air is because if it is higher than a certain point, noise restrictions are ignored.

You need to break up the tone so it isn't resonating in your cab. You should put another "box" in line to increase the volume somewhere. It DOES matter where you put it. (Think standing wave on a jump rope, if you have the point where it isn't moving in the standing wave, NODE, then putting a muffler there won't help, it needs to be in the high motion area, ANTINODE)

Don't sweat calculating nodes or anti-nodes, just don't put it 1/2 way down the pipe! Off set it and see what it does.

[Danimal]

As for hangers and such, get some sand bags or something of that sort, pull the exhaust off the hangers and set them at "running" height using jack stands and sand bags and fire it up. If the tone is still in the cab, it isn't a structure borne noise. If it goes away, start fiddling with your mounts! Get good rubber isolators and make sure you have plenty of room for fore/aft growth in the pipes with no binding. About 1/2" to 1" should be good. If your pipes bind up with thermal expansion, you WILL have radiated noise issues.

I'm not an expert, just worked at Walker and Bosal exhaust for about 12 years total. Most of my experience has been with OE stuff so the goal is quiet unlike hot rod stuff which obviously has a focus on power. Premise is the same, it's all Jell-O. Push it down here, it pops up somewhere else!

[Beck]

I finished up the exhaust system on my old truck today. (Check earlier in the post for truck specifics)
I kept the 3" down pipe from the turbocharger. Behind that I installed a 3" stainless steel flex fitting. Then I reinstalled the 3" glasspack that I used before. The glasspack dumped directly into a DynoMax stainless steel muffler with 3" in and dual 2 1/2" out. A friend with a muffler shop worked several hours and ran 2 1/2" exhaust pipe out the rear of the truck. He managed to get the pipe over the rear axle and cleared everything. All of the hangers are rubber mount and mount to the frame. Nothing contacts the cab or bed.
The difference is amazing. The motor is still making it's diesel sounds but the exhaust is quite. The droning is gone. I like it!
Unfortunately on the way to the exhaust shop I noticed the windshield fogging. On the way home the heater core was dripping on the floor. Just when I thought I was done.... I start another project.

[Charlie Chops 1940]

One forward, two back??? Anyway, nice to hear that the exhaust is livable now. Sometimes it takes a year or two to work the bugs out.

Charlie

[taxpyer]

Caterpillar had a D6 model dozer in the 70's where the exhaust noise used to make operators sick enough to throw up,,,  they had to retrofit the exhaust systems with an updated version to eliminate the problem. All as a result of exhaust "drone".  
Hope you find a solution to this so you can enjoy your truck.