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WendyArmbuster
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Joined: March 03, 2006
Posts: 349
Location: Springfield, MO
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 Posted: Tue Oct 15, 2024 7:22 pm Post subject: Can I safely add a resonator to my exhaust outlet? |
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I have a stock 1978 bus with 72-74 heat exchangers and an Ernst exhaust I got at Bus Depot a few years back. It looks great and is still holding up, but it has never been as quiet as I wanted, and I can't believe that buses were this loud off the lot. I would say with high confidence that I have no exhaust leaks. It just seems loud, especially inside the bus. I have made efforts at sound dampening in the rear of my interior thinking it was just a resonation sound, but to no avail.
There are lots of options for short resonators, and I'm thinking about welding a triangle flange onto one end of one and bolting it to the outlet of my Ernst where the curvy tail pipe is currently attached. I have about 15 inches from the flange to the side of the bus, and there are resonators shorter than that. Would it cause enough restriction to mess with my temperatures? That's one thing I'm not willing to sacrifice. Would it even do any good?
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Brian Z
1978 Westfalia |
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raygreenwood
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Joined: November 24, 2008
Posts: 23134
Location: Oklahoma City
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| Posted: Tue Oct 15, 2024 9:31 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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| WendyArmbuster wrote: |
I have a stock 1978 bus with 72-74 heat exchangers and an Ernst exhaust I got at Bus Depot a few years back. It looks great and is still holding up, but it has never been as quiet as I wanted, and I can't believe that buses were this loud off the lot. I would say with high confidence that I have no exhaust leaks. It just seems loud, especially inside the bus. I have made efforts at sound dampening in the rear of my interior thinking it was just a resonation sound, but to no avail.
There are lots of options for short resonators, and I'm thinking about welding a triangle flange onto one end of one and bolting it to the outlet of my Ernst where the curvy tail pipe is currently attached. I have about 15 inches from the flange to the side of the bus, and there are resonators shorter than that. Would it cause enough restriction to mess with my temperatures? That's one thing I'm not willing to sacrifice. Would it even do any good? |
The Ernst mufflers are awesome quality and make a slight noticable difference in performance.....on type 4 engines in 411/412 and 914. I do not know that it will make a performance difference on a bus.
The reason they work better than say a Wagner, Leistritz or Dansk...is also the reason why they are a bit noisier. They have slightly larger diameter pipes inside and larger perforations along with a coupole of liters of larger displacement.
That being said, its an interesting question. If you look at the "damper" style mufflers used on type 4 (and type 3)...which has a little bit of a different layout inside.....that finak tailpipe that exits from the center of the muffler instead of the end....is actually a double wall damper. They were also a good deal more quiet than the end exit mufflers. So, there is some evidence to say that a resonator may help you. Ray |
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 13481
Location: West Coast, USA
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| Posted: Tue Oct 15, 2024 9:54 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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Resonator vs. Muffler…
Resonators typically fight specific pitches, like drones and boomy acceleration. They are designed for a specific frequency or engine sound reduction, not general muffling.
I'm not saying don't do it, but it would be worth your time to analyze the sound spectrum that your engine is producing and find a resonator that works against the low-end spikes that your engine makes.
Robbie
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rob.e
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Joined: August 07, 2013
Posts: 63
Location: Oxford, UK
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| Posted: Wed Oct 16, 2024 1:50 am Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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I added an additional muffler (resonator) to my pacesetter to see if i could make it a bit quieter. to be honest it really didn't make that much difference so i took it off
if you're worried about noise get some noise-cancelling ear buds/ headphones. i do long trips in the bus with my apple air pods in my ear - even if i don't have music on they do a great job at cutting out the repetitive /tiring noise.
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23134
Location: Oklahoma City
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| Posted: Wed Oct 16, 2024 12:21 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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| airschooled wrote: |
Resonator vs. Muffler…
Resonators typically fight specific pitches, like drones and boomy acceleration. They are designed for a specific frequency or engine sound reduction, not general muffling.
I'm not saying don't do it, but it would be worth your time to analyze the sound spectrum that your engine is producing and find a resonator that works against the low-end spikes that your engine makes.
Robbie |
This ^^^^
Resonators arrest harmonic resonations. It could arrest a single pitch or several depending on the design. Its rare that a REAL resonator actually lowers sound decibles. But it can change the sound PITCH or get rid of harmonic droning as was said.
You CAN make a resonator that is...somehwere in between a muffler and resonator. Actually thats all the type 4 muffler is. Its a combo resonator and muffler.
Here is a picture of the "damper style" tail pipe muffler used on 411/412 and 914 (maybe some bus too) ...that I was describing in my last post.
https://www.ebay.com/itm/266866149492
That bulge around the tailpipe is a chamber. There are perforations on the main pipe. Where they are whether partial length, full length of just cattered and what size they are....are what tune where the gas enters that dead end chamber. It changes what frequency gets delay (if not neutralized).
It changes the sound....but does not lower its decible level.
So if thats all it is...its a resonator.
BUT....if there is also either rockwool, fiberglass or metal cloth matrix packed into that dead end chamber....its also...partially....a muffler. It can also slightly lower decibles.
To this day I still have not had one of those spare to cut open and see how its made.
Ray |
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WendyArmbuster
Samba Member
Joined: March 03, 2006
Posts: 349
Location: Springfield, MO
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| Posted: Wed Oct 16, 2024 3:55 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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I drove a perfectly stock 1979 California bus a few years back, and I was startled to experience how quiet it was. It was just a world of difference between my bus and that bus, but that's the only one I've ever experienced that was as quiet as I'm hoping for. I remember it had a very complicated looking exhaust system.
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Brian Z
1978 Westfalia |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23134
Location: Oklahoma City
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| Posted: Wed Oct 16, 2024 4:27 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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| WendyArmbuster wrote: |
| I drove a perfectly stock 1979 California bus a few years back, and I was startled to experience how quiet it was. It was just a world of difference between my bus and that bus, but that's the only one I've ever experienced that was as quiet as I'm hoping for. I remember it had a very complicated looking exhaust system. |
Hmmmm...1979 2.0L. Complex....meaning it probably had the catalyst and cross over pipe. Yes. More quiet, more complex, more restrictive, runs hotter.
The most quiet standard muffler type 4s...1.7L and 1.8L engines in buses, 411/412 and 914 are the "damper" style muffler with the tailpipe that exits in the center of the muffler.
But they ran a little warmer because they were a little more restricted. Pretty much the more restricted the muffler the quieter it is. Ray |
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 13481
Location: West Coast, USA
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| Posted: Wed Oct 16, 2024 8:13 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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The Type 1 buses all had those "damper pipe" style tubes before the curved tip. Driving without it encourages a low frequency hum below 2,500 RPM but I don't hear a difference above that.
Talking online about the noise a car makes is useless unless someone can isolate the noise they are describing. Either frequency, load/throttle/speed measurement, or any other video/description would be helpful.
MOST if not all of the hundreds of buses I work on had or have driveline alignment issues. That is, the vibrations from the powertrain are transferred into the chassis through misaligned engine mounts, transaxle mounts, and shift rods. This creates an extremely loud cabin resonance related to engine speed, making people think their engine is loud. Even the best balanced engines can suffer this with careless installation. (Bentley has an order of bolt-tightening for a reason. Are we all following it every time?)
There are decibel apps you can get for your phone to see this… Well-sorted stock buses have no discernable engine noise at 60+mph. That is, you can accelerate to 60+, push the clutch in, and the sound level doesn't change. In other words, the driveline/engine/gearbox/exhaust can not be heard over road/tire/wind noise.
Aftermarket engine/transaxle mounts also play a huge part in transmitting noise through their stiffness. So does fan noise/balance. And bearing clearances in your transaxle. And end play. And tire tread. And…
Bolting on a resonator can be helpful, but don't think it's a substitute for spending hours, if not years, dialing in the sneaky few details that VW took to the grave with them.
I encourage anyone giving sound reduction advice to post videos of their bus cabin at speed. Decibel readings are good too. (63dB @ 55mph here.)
Here's my friend chatting at 55mph, all you should hear is tire noise:
Link
At the 0:42 and 0:30 marks, you can hear what the back of my 7-seater project bus sounds like. 72-74 exhaust setup, no cat, crossover, or resonator:
Link
So go ahead, analyze the noise your engine is making. Fight them at the source and you'll be miles ahead.
Robbie
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 52335
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| Posted: Wed Oct 16, 2024 8:51 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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| I have never tried this on a bus, but back during the 1940's and 1950's, some cars came with the tip of the tail pipe slightly collapsed, this would certainly change the tone of the exhaust if not knock the decibel level down a bit. It would be easy enough to remove the bus tailpipe and use a dull chisel to collapse the end of the pipe by 30% or so. You would want to collapse the inside of the curve, leaving the outside of the curve where the velocities are going to be the fastest nice and smooth. If you do this get back to us to let us know how it works. |
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raygreenwood
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Joined: November 24, 2008
Posts: 23134
Location: Oklahoma City
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| Posted: Thu Oct 17, 2024 6:56 am Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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| Wildthings wrote: |
| I have never tried this on a bus, but back during the 1940's and 1950's, some cars came with the tip of the tail pipe slightly collapsed, this would certainly change the tone of the exhaust if not knock the decibel level down a bit. It would be easy enough to remove the bus tailpipe and use a dull chisel to collapse the end of the pipe by 30% or so. You would want to collapse the inside of the curve, leaving the outside of the curve where the velocities are going to be the fastest nice and smooth. If you do this get back to us to let us know how it works. |
Oh yeah! Small tailpipe details make a big difference.
At one point in time........the right end exit Wagner muffler I had bought NOS and was putting on my 1.7L 412 came without a tailpipe so I used the rusty one from my old muffler for a while.
Months later at the same place I bought the NOS Wagner, I found a new 3-bolt tailpipe. When I compared to the old rusted stock one.....it found was identical (same curve, same pipe diameter and thickness, same angle welded to the flange.....bolted right up!).
But....it was the same in all but two ways.
1. The total length of the outer opening of pipe was right at 19mm longer.
2. The outer end/opening was slightly flared like a megaphone. It was subtle. Maybe 3/16" bigger in diameter at the exit than stock. You had to look at it from the side to see it.
BUT.....the sound was totally different. The pulses were more distinct but less sharp. It was neither more or less quiet.....but it totally made driving at cruise speed less long term annoying and the exhaust note echoed less driving through narrow neighborhoods.
Years later, someone told me it was a dealer option tailpipe at one time. He called it a Ralley tailpipe.
Yes, small mods like a dent in the end of a type 4 tailpipe can make a big sound difference. Ray |
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WendyArmbuster
Samba Member
Joined: March 03, 2006
Posts: 349
Location: Springfield, MO
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| Posted: Thu Oct 17, 2024 8:08 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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| Quote: |
| Bolting on a resonator can be helpful, but don't think it's a substitute for spending hours, if not years, dialing in the sneaky few details that VW took to the grave with them. |
I think this is probably the best course of action, but I've done a lot and not sure where to go from here. I had my transmission rebuilt, and that did help because it was rumbling. I replaced my rear engine rubber mounts. I have not replaced the transmission/engine mating area rubber mounts, or the rubber on the front fork, but those seem to not be available anymore anyway, and mine still seem soft. The shift bushing is soft, perhaps too soft. It's loud at idle and while driving. I just had my engine rebuilt, and there is way, way, way less mechanical noise now, but the exhaust is still just annoying. I used to have a stripped exhaust head stud that always caused a leak, but that's gone now, and it's just no quieter. I assumed a lot of what made that '79 so quiet was the awesome modern head to manifold joint without those lame copper ovals.
My bus sounds hollow and echo-ey, and it's louder inside than outside. When somebody else drives it and I'm not in it, it doesn't seem like such a problem, but it's still not quiet. It's the low frequency that bugs me. You could not film a video with dialog in my bus unless everybody was talking very loudly.
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Brian Z
1978 Westfalia |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 52335
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| Posted: Tue Nov 05, 2024 1:47 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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| raygreenwood wrote: |
| Wildthings wrote: |
| I have never tried this on a bus, but back during the 1940's and 1950's, some cars came with the tip of the tail pipe slightly collapsed, this would certainly change the tone of the exhaust if not knock the decibel level down a bit. It would be easy enough to remove the bus tailpipe and use a dull chisel to collapse the end of the pipe by 30% or so. You would want to collapse the inside of the curve, leaving the outside of the curve where the velocities are going to be the fastest nice and smooth. If you do this get back to us to let us know how it works. |
Oh yeah! Small tailpipe details make a big difference.
At one point in time........the right end exit Wagner muffler I had bought NOS and was putting on my 1.7L 412 came without a tailpipe so I used the rusty one from my old muffler for a while.
Months later at the same place I bought the NOS Wagner, I found a new 3-bolt tailpipe. When I compared to the old rusted stock one.....it found was identical (same curve, same pipe diameter and thickness, same angle welded to the flange.....bolted right up!).
But....it was the same in all but two ways.
1. The total length of the outer opening of pipe was right at 19mm longer.
2. The outer end/opening was slightly flared like a megaphone. It was subtle. Maybe 3/16" bigger in diameter at the exit than stock. You had to look at it from the side to see it.
BUT.....the sound was totally different. The pulses were more distinct but less sharp. It was neither more or less quiet.....but it totally made driving at cruise speed less long term annoying and the exhaust note echoed less driving through narrow neighborhoods.
Years later, someone told me it was a dealer option tailpipe at one time. He called it a Ralley tailpipe.
Yes, small mods like a dent in the end of a type 4 tailpipe can make a big sound difference. Ray |
Saw this a few days ago, wonder if there is much difference in the sound.
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SGKent 
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Joined: October 30, 2007
Posts: 42528
Location: at the beach
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| Posted: Tue Nov 05, 2024 4:33 pm Post subject: Re: Can I safely add a resonator to my exhaust outlet? |
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1971 had a small exhaust that caused back pressure. Got a nice extractor exhaust and much more power as a result. The price was it was louder. But the downside is I got noise tickets - and frankly it wasn't THAT loud.
You might make one check where you put a rag or leather shoe sole over the exhaust to plug it and make sure that stalls the engine. If it does not then you may be hearing an exhaust leak. You can also have a "muffler cone insert welded or screwed into the tip of the exhaust, it will dampen the noise, but you will also loose power.
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