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Exhaust Resonance

ak diesel driver said:
Previous post should have said 1500 rpm.
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Maybe wrong gear for conditions and "Lugging" a high speed diesel. Sure there could be something wrong and even if there is it's letting you know it doesn't want to run at this RPM/load/temp. It's like you found a harmonic. Drop it into 3rd and doing so will warm it up faster as well.

You could try varying the timing. At 45 MPH the TCC locks up and NVH is one reason it locks at such a high MPH. IMO it could lock at 35 MPH under some conditions if GM used a better TCC clutch that could hold it.

Looking for other things may be coolant hoses, PS hoses, etc. rattling on something.
 
WarWagon said:
Maybe wrong gear for conditions and "Lugging" a high speed diesel. Sure there could be something wrong and even if there is it's letting you know it doesn't want to run at this RPM/load/temp. It's like you found a harmonic. Drop it into 3rd and doing so will warm it up faster as well.

You could try varying the timing. At 45 MPH the TCC locks up and NVH is one reason it locks at such a high MPH. IMO it could lock at 35 MPH under some conditions if GM used a better TCC clutch that could hold it.

Looking for other things may be coolant hoses, PS hoses, etc. rattling on something.
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The Wester's tune I had in my 3500 locked at 30-35 mph. With a 9400 lb truck I hated that. Maybe in my <6000 lb 1500 it would be fine.
 
Colder temps cause steel to get more brittle, more brittle means it is harder. I have noticed the sound of the exhaust changes quite a bit when the air temps gets real cold. I would think with the warm exhaust flowing through the pipes that they would not be so brittle. It might be that the outside of the pipe is still more brittle from the cold air surrounding the pipe and causing the resonance sound. Might try wrapping the pipe with some insulation and taking it for a short run to see of that theory holds true.
I do know when temps get to about ten above zero, You clip a reflector post with a snow plow and they snap right off at ground level, clip a delineator post at thirty degrees and the just bend over. LOL Dont ask Me how I know this. LOL :)
 
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When I swapped my EGR intake for non-EGR, I picked up some noise - seemingly from the exhaust. Later in my build, when I put the water-to-air intercooler on I picked up some serious resonance on the highway. I later found the heat exhanger was touching the hood, but even after moving it so it doesn’t rub it still gives me some resonance. When I mentioned it to my brother as he was in the passenger seat he didn’t know what I was taking about. Then he moved his head over near the driver seat and he could hear it. Sure enough the further away from the driver side window the quieter it gets. I have yet to figure out how to fix it.

So I guess 2 things: 1. It doesn’t surprise me that a change in the intake/turbo changes the sound and 2. Does the sound change if you move your head to another part of the cab?
 
I think the intake silencer is to reduce whistle and any turbo air rush noises from turbo deceleration. The exhaust is the much louder component here as its expanded from heat and has the velocity. I doubt it will change anything putting the silencer back on.

A lot of vehicles can get some air "reverberation" from different windows being down. You might have a little more air leak on the driver's side door. Usually, the rear windows down will create a killer air noise.

My 3" dp and 4" exhaust has a lot of drone at certain RPM's. I can hear some different tones and vibrations when I am towing my gooseneck and burning more fuel running under sustained boost going uphill. Sometimes it gets really rough sounding from combo drivetrain and exhaust. I think the Timbren's really contribute in my scenerio. My truck with 254K miles and lots of worn out parts suspension, exhaust hangers, engine mounts, U-joints, tired IP (overall engine) it would be very expensive to try to figure it out. I am living with it for the foreseeable future.

I'd be inclined to look at exhaust pipe and hangers and see if you can nip up the Vband clamp. Maybe put another hanger in between the longest space between ones now. Could it be air pushing on the tailpipe under speed changing the load on the rear hangers also being stiff in cold just changing the rigidity of the pipe/hangers slightly to act like a different tuning fork ????

Good point above looking at all sheet metal parts might also be a good idea. The dang bell housing dust cover on the clutch or torque converter has caused me problems twice before. I had to bend mine and put some washers under a screw to quiet it. It would only rattle at certain RPM's, loads, and times. It was pesky and not always a consistent sound.
 
We have two Suburban K2500s, a '94 and a '99. Both have ATT setups, the '99 with a K47 airbox and the '94 with a Heath airbox. The '94 is way more quiet as far as engine noise at all speeds.
 
I think you should try a different turbo and send the ATT to me. ;)

Maybe add one of those whisler exhaust tips to overpower the drone!

Try the intake piece since you still have it around and it’s free. I thought @schiker (is that you hike in SC?) had it right on his first post on this thread. Just getting the air flow to change some how will help. Think changing airflow through a straight trumpet. That is all resinator does. You have welding skills- make one.
 
Yeah, I use to hike and canoe a good bit and I am from SC but uhh it was 20 years ago I started on the forums and started with the username and just kept it with different sites. Hiked places in SC, Western NC, and once or twice some trails in VA. Nothing real long mostly 1 overnight loop trails. I haven't camped in a few years now. Think my longest was around 27 miles can't remember exactly that was a Friday late afternoon return Sunday afternoon. I still hike some but not like back then.
 
Yes on colder air because it is more dense, and sound waves travel differently. The greater amount of oxygen going through and burning more fuel mean greater amount expanding afterwards. So it is like the trumpet player blowing a little harder while holding the same note.
 
So a report back, I've only had one day of the right weather. Yesterday was 21 above today was cold enough but had ice fog so I couldn't drive fast enough. Almost couldn't keep the windshield open enough to see, defrost on high and only could keep the bottom 3-4 inches clear. Anyway the drone is still there but different, not quite as loud and not as metallic sounding. Little lower pitched. I'll leave it on for a bit and see if that's still accurate.
 
Will L. said:
Resinator.

If you download a tuning app on your phone or have a microphone and an oscilloscope, you can know the frequent being created and get a resinator tuned to that frequency to eliminate it. That works perfect but is pricey. Most people buy the $180 versions that are “close enough” and knock out most of the sound..
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Measuring what frequency the only way to go then a smaller diameter side pipe should be installed to cancel it out. I've seen some custom setups where a section of the side pipe slides in/out so it can be fine tuned by the end user.
 
I haven't heard of the Helmholtz thing I have heard of resonators. I like the idea of the Helmholtz not restricting flow. I like the resonator's compactness.

A long time ago I saw a friend's Dodge with a resonator. IIRC my Dad's '72 caddy with 472 cubic inch engine had a resonator in addition to the muffler. Side note everything on that caddy was as big and heavy some even heavier than my 3/4 ton truck. That thing was a tank.

There are a few youtube videos of resonators. Saw one guy build a Helmholtz but he didn't install it. From this video, the FTE appears it has 2 paths for the air to flow and seems like a wing where it creates 2 paths and I am figuring it allows a speed differential and again I guess when they remix they cancel some drone.

I thought this was a good video. My truck drones but not near anything like this Dodge. AK does your truck drone approach this truck and then attenuate or vibrate the exhaust pipe to sound more metallic?


From my brief sound testing just lowering the frequency seems to make the sound more pleasant and seems to on this Dodge.
 
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