Help me quiet down my truck please

Beck · October 11, 2009, 11:26:34 AM

My current ride is destroying my hearing! I am talking permanent hearing damage here. I drove it out to Bonneville for speed week. That was about a 3200 mile round trip. My hearing will never be the same. This weekend I drove it to the Hunnert Car Pileup in Morris IL. That was about a 550 round trip.
Here are the details of my truck. It's a '62 Chevy PU with a stepside bed. The motor is a Cummins 4 cyl diesel with turbocharger. The transmission is a 400TH. I'm running a Chevy truck 10 bolt rear with 2.50 gears. The exhaust is a 3" downpipe from the turbo to a 3.5" dia pipe under the truck. There is a 3" glasspack at the front of the 3.5" pipe. I have to run the exhaust out in front of the rear tire since the exhaust will not clear the rear axle and rear mounted fuel tank. I have some homebrewed sound proofing in the cab of the truck. I used a rubber/aluminum home construction material on the floor first. The firewall has 2 layers. This material is designed for use around windows during construction to seal water from the wood. It is self adhesive. (Thanks Charlie for this tip) On top of this I used the standard hot rod style pad with dual foil over the ground felt. Again there is a dual layer on the firewall. There is then carpet over everything. There is some area on the top of the firewall that you just can't get to that isn't covered. This would be the bottom of the windshield wiper/air intake box. I was expecting a problem so everything that can be covered is.
This was the configuration I ran to Bonneville. Before the trip to Morris I added a home built baffle. In the auto magazines I had seen a spiral baffle system. I attempted to copy one. I used a piece of 1 1/4 pipe and cut some spiral washers to weld on the outside. This slip fit into the 3.5 tailpipe. I built mine 8" long with 3 spirals. I welded a nut on the front spiral and drilled a hole in the tailpipe to bolt it in. From the outside of the truck it sounded slightly quieter. I also added some 3/4" thick sound proofing foam to the full bottom of the hood.
The truck drones on.
At this point I am thinking it isn't exhaust noise but resonance from the motor. When I get off the fuel to slow down the noise does reduce. When load is on the motor it drones in the cab. I am considering a flex pipe at the joint of the 3" turbo down tube and the 3.5" exhaust piping.
I an turning the motor a little faster than I would like at highway speeds. At 75 mph I am running about 2350 rpm. The turbo is making about 9 pounds of boost at this speed so I am loading the motor somewhat. The exhaust gas temp is still very acceptable at about 750 F.

enjenjo · October 11, 2009, 11:47:46 AM

Why not try an exhaust wrap? If its the pipe resonating that should help. A flex joint might help too. Also a pad on the inside of the hood, and inner fenders should help.

Beck · October 11, 2009, 11:58:16 AM

Quote from: "enjenjo"Why not try an exhaust wrap? If its the pipe resonating that should help. A flex joint might help too. Also a pad on the inside of the hood, and inner fenders should help.

By exhaust wrap are you talking about the fiberglass wrap normally used for heat control? I have seen some foil type wraps also from one of the vendors in the major custom automotive magazines.
I have added the padding under the hood with no help.

Mac · October 11, 2009, 12:18:05 PM

You may also be developing exhast noise resonance if you have any long straight runs of pipe either before or after the muffler.

I dealing with the same thing on the 3" exhaust I just put on my `63 C-10. I ran the downpipes to the pass. side into a 2 into 1 collector, outside the frame, then straight back to a muffler just past the cab. That makes a straight run of like 5 ft. and I'm getting some drone inside the cab at cruise. I'm thinking of putting a resonator in between the collector and the muf to see if that cancels the resonance.

enjenjo · October 11, 2009, 12:30:57 PM

Quote from: "Beck"
Quote from: "enjenjo"Why not try an exhaust wrap? If its the pipe resonating that should help. A flex joint might help too. Also a pad on the inside of the hood, and inner fenders should help.
By exhaust wrap are you talking about the fiberglass wrap normally used for heat control? I have seen some foil type wraps also from one of the vendors in the major custom automotive magazines.
I have added the padding under the hood with no help.

Yes. On our big trucks we used it on the turbo pipe. from the turbo, to down below the cab as part of a noise package. You might consider a baffled muffler too.

sirstude · October 11, 2009, 01:28:59 PM

On one of the board I am on I think, someone had the complaint of droning exhaust in the cab and they said the fix was to put bends in the pipe. Also, make sure you have good rubber mounts between the pipes and the frame. Unless you have a unibody and have to, never mount the pipes to the body, only the frame. I learned that one the hard way when I ran an exhaust shop. You also might look into one of those flexible exhaust pipe couplers to isolate things a bit. Biggest issue is the one you say cannot be fixed, the outlets in front of the rear wheel.

Doug

Charlie Chops 1940 · October 11, 2009, 02:55:06 PM

Tom,

Fabricate a chunk of rectangular exhaust pipe to go over the rear ensd. Your 3" diameter pipe is just over 7 sq. inches. A rectangle 1.5X5 would be slightly larger. Faily easy to fabricate out of 16ga.

Charlie

Beck · October 11, 2009, 02:58:08 PM

Quote from: "enjenjo"
Quote from: "Beck"
Quote from: "enjenjo"Why not try an exhaust wrap? If its the pipe resonating that should help. A flex joint might help too. Also a pad on the inside of the hood, and inner fenders should help.
By exhaust wrap are you talking about the fiberglass wrap normally used for heat control? I have seen some foil type wraps also from one of the vendors in the major custom automotive magazines.
I have added the padding under the hood with no help.

Yes. On our big trucks we used it on the turbo pipe. from the turbo, to down below the cab as part of a noise package. You might consider a baffled muffler too.

After reading this post I recalled that I already have the down pipe from the turbo to the larger tube wrapped with the fiberglass. It just so happens that we wrap copper tubing used as steam tracing at work with the same material. The fiberglass wrap protects from operator burns where the tracing isn't covered with thick piping insulation.

Beck · October 11, 2009, 03:05:28 PM

Quote from: "Charlie Chops 1940"Tom,

Fabricate a chunk of rectangular exhaust pipe to go over the rear ensd. Your 3" diameter pipe is just over 7 sq. inches. A rectangle 1.5X5 would be slightly larger. Faily easy to fabricate out of 16ga.

Charlie

The big problem with that is my fuel tank is right behind the axle. I have considered the rectangular over-pipe, but after it is over the axle it would need to come under the fuel tank which is LOW. To avoid the tank it would have to snake through the lief spring since the tank extends frame rail to frame rail.
Who ever engineered this truck wasn't very bright! Oops, that was me.

How much restriction would it be to exit the rectangular tube into the side of a 3" round exhaust tube? This would create a T. I could run the 3" round tubing to both sides for dual outlets.

wayne petty · October 11, 2009, 06:58:41 PM

droning from the pipe... through the walls of the pipe.... why not wrap a layer of shim stock or thin metal and install a few muffler clamps on the middle of the pipe to see if the pipe is actually resonating.. the damping force of the clamps will reduce the sound output of the sidewalls of the pipe... and its totally removable.. if not overtightened.. because you used shim stock under the clamp... it will not have damaged the pipe...

thats a start...

as for droning out the end of the pipe... i will think about it..

after driving my GTO for 5 years with the turbo mufflers bolted to the collectors it took another 5 years before i could hear a vacuum leak...

way did you say..

?

Beck · October 11, 2009, 07:31:19 PM

I guess I should put this information out there also since it could be contributing to my problem.
My 3.5" "exhaust" pipe is actually schedule 10 316 stainless steel 3" pipe. We had some off fall from a project at work so I made use of it. This is 2 to 3 times heavier than regular exhaust pipe. Should this extra heavy tube help or hurt with the noise?
It is mounted with rubber hangers. The front hanger is held on with the seat belt bolt through the cab floor. The rear hanger is held on with the step from the step-side bolts. So both of these are on body structures not frame structure. It would be possible for the noise to transmit through the rubber to the body. There are no frame structures where the pipe runs to mount it to.

enjenjo · October 11, 2009, 07:54:11 PM

Quote from: "Beck"I guess I should put this information out there also since it could be contributing to my problem.
My 3.5" "exhaust" pipe is actually schedule 10 316 stainless steel 3" pipe. We had some off fall from a project at work so I made use of it. This is 2 to 3 times heavier than regular exhaust pipe. Should this extra heavy tube help or hurt with the noise?
It is mounted with rubber hangers. The front hanger is held on with the seat belt bolt through the cab floor. The rear hanger is held on with the step from the step-side bolts. So both of these are on body structures not frame structure. It would be possible for the noise to transmit through the rubber to the body. There are no frame structures where the pipe runs to mount it to.

Thick pipe makes the droneing worse.

Dr Flowgood · October 21, 2009, 10:30:30 AM

I would try a better muffler, the glasspac isnt doing a whole lot of "muffeling" something like a dynomax super turbo muffler or an oem type (more restrictive, but quieter.

Its harder to quiet down a larger pipe. Turbos dont like a restrictive exhaust but maybe you can find a happy medium. maybe you could make the mufflers easy to swap out and have a quiet muffler for long trips and put the other one on for performance.. just a thought.

Doug

"There is a 3" glasspack at the front of the 3.5" pipe. "

Beck · October 21, 2009, 11:13:51 AM

I put some sound deadener insulation on the bottom of the hood. I covered everything. It didn't help.
I made an insert for the tailpipe. It was a copy of the smaller pipe with spiral washers on it. I used 8 inches of 1 1/4 tube with 3 spirals around it. It didn't help.
I am now designing a complete new exhaust system. I have to get the outlet behind the truck instead of in front of the tire.
I have thought of another possible problem. The little diesel has a turbo which I upgraded with a slightly larger one. One of the tricks with diesel turbos to get them to spool up quicker is to install smaller exhaust housings. My turbo originaly had a 16 cm exhaust housing. I installed a 12 cm housing. I am reving the motor harder than when it was in the original application. I may be causing backpressure due to the smaller housing. I may have to try the big one again. I don't know if this would cause noise. My EGT temps are not high so this may not be the problem. I'm running at 8 to 9 psi boost at highway (75 - 78 mph) speed.
I haven't given up yet. I'm wearing ear plugs when driving now. Each of the last 2 weekends were over 550 miles in the truck going to shows. I now have over 7000 miles on it this year. It is reliable, just loud in the cab.

wayne petty · October 21, 2009, 12:03:46 PM

Quote from: "Beck"
It is mounted with rubber hangers. The front hanger is held on with the seat belt bolt through the cab floor. The rear hanger is held on with the step from the step-side bolts. So both of these are on body structures not frame structure. It would be possible for the noise to transmit through the rubber to the body. There are no frame structures where the pipe runs to mount it to.

i would say yes.... perhaps... it is coming through the floor... where it is hung from the floor board...

or through the rear of the cab from the bed... sound does transmit well through large flat panels..

before replacing the exhaust.. perhaps.. changing to different hangers...
there are rod type isolators.. so you can bend long pieces of rod to go a little farther than you might with something else..

i have not seen your truck... how about having somebody in the cab with you.. feel the different panels with their hands while you drive at a droning speed.. see where its coming through..

have you got any custom exhaust shops nearby .. you could ask for ideas in person. from somebody who does it for a living. just having your truck on their lift and people seeing it will bring them business..

wow.. i stopped to google exhaust hangers pdf... and found this scientific paper on them...

http://www.me.mtu.edu/~mrao/sae-nvc-121.pdf

i know there is more information on this site

http://www.walkerexhaust.com/support/exhaust101/componentsAndDesign.asp

and.. the last thing.. do you know anybody with a electronic ears set.. clip on microphones that connect to a central box so you can see which part makes more noise..