Exhaust baffle modification

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In summary, the muffler is a basically a straight-through tube with fiberglass packing that is too loud. The baffle came as just an insert that makes the gas flow around it, never through it, and has two small bulges which i assume are to speed up/slow down the flow to disturb the sound. The muffler can be modified to increase its effectiveness without using fiberglass, but this will restrict the flow of the exhaust.
  • #1
Stephen Ryan
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TL;DR Summary
Looking to learn the scientific way to quieten a motorcycle exhaust baffle
Hi everyone.

I don't have much knowledge in physics but I am trying to take a scientific approach to silencing my motorcycle exhaust.

The muffler is a basically a perforated straight-through tube with fiberglass packing (too loud).

The baffle (only knocks one decibel off) came as just an insert that makes the gas flow around it, never through it, and has two small bulges which i assume are to speed up/slow down the flow to disturb the sound. Not very effective.

I have drilled some holes in preparation for filling the baffle with fiberglass. The plan was to drill along the entire length but for performance reasons id now like to improve the flow a bit too if possible.

Is it possible to modify this baffle to increase its effectiveness without using fiberglass (just holes to manipulate the gas flow)

Im keen the learn the physics of how all this works as i also have an issue with the pulses not being timed correctly to enhance efficiency but that's a job for another day!

Any pointers/advice is much appreciated
 

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  • #2
You;ll need to study up on the basics of how mufflers work.

You can just deaden the sound by restricting flow at expense of power loss from backpressure,
You can use cancellation by reflecting sound waves together, that's 'destructive interference'.
probably your muffler was designed to reduce only high frequencies giving a throaty roar..

Here are two articles to get you startedhttps://www.dragzine.com/tech-stori...ffler-design-and-sound-absorption-strategies/
https://www.acoustics.asn.au/conference_proceedings/AAS2005/papers/34.pdf
In my day I had wide open Dunstall megaphones
they used 'constructive interference' to increase sound level like a trumpet
The town policeman told me :
"Jim - i'd just pulled a guy over for a teeny bit noisy muffler. Then you went by and i was doggone embarrassed",
as he wrote the ticket .

old jim
 
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  • #3
Back in the day, I once bought a used Honda 350. The previous owner had installed a pair of cheap mufflers that did not do much muffling. So I welded 9/16" ID washers over the outlets, which got the noise level down to about that of the original factory mufflers.
 
  • #4
Very interesting reads. The complexity of sound deadening 'baffles' me (hehe). I now have some more ideas I'd like to start prototyping. This has gone from a curious project to something that will consume me!
 
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  • #5
I don't know if this helps, but rather than drilling, you might consider rolled perforated metal, or something like this. I'd probably choose something like ceramic fiber insulation to fill the void if needed. It may take some fine stainless screen to prevent erosion through the perforated surface.

Most motorcycle engines have the exhaust designed for sound reduction, but more important consideration is given to torque, throttle response, and operating behavior of the engine, so you can make it quieter, but it's operation may change.
 
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  • #6
I've built several mufflers back when I was still riding/tinkering with bikes, although "quiet" was never the goal!

I started by drilling tube, very tedious, then discovered expanded mesh, roll into tube shape, weld ends together, but the perf tube above would be much better/easier.

I just used stainless steel wool as the packing material. The first ones were too quiet, so I started taking off length and re welding till I got it so it wasn't so loud that the police would instantly pull me over, but still sounded awesome, and more importantly flowed well (no welding washers over the exhaust!) and no need to really look at the rev counter for shifting.
 
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  • #7
wide open Dunstalls, ca 1965
243582


that's a '56 Indian.
just today noticed a '57 at a shop in New Cumberland Pennsylvania..
Sigh...
 
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  • #8
You have straight-through muffler which is loudest design. Cut open some OEM mufflers and you'll see that end of central tube is actually closed and exhaust goes through multiple chambers along with reversal of flow in order to reach outlet. This lengthens exhaust flow-path by 3x along with lots of expansion. Result is quieter exhaust with minimal restriction. Modern OEM mufflers are miracles of design requiring no packing material (which needs to be replenished regularly in old days).
 
  • #9
Here's cut-away of factory muffler. This one has 4 different chambers that gases go through to reach outlet.
 

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1. What is an exhaust baffle?

An exhaust baffle is a component in a vehicle's exhaust system that helps to reduce noise and regulate the flow of exhaust gases. It is typically a perforated tube or plate that is placed inside the exhaust pipe.

2. Why would someone want to modify their exhaust baffle?

Some people may want to modify their exhaust baffle to increase the sound of their vehicle's exhaust or to improve the performance of their engine. However, it is important to note that modifying the baffle can also have negative effects on the vehicle's emissions and may not be legal in all areas.

3. How is an exhaust baffle modified?

An exhaust baffle can be modified by removing it completely, drilling holes in it, or replacing it with an aftermarket baffle. The specific method of modification will depend on the type of exhaust system and the desired outcome.

4. What are the potential risks of modifying an exhaust baffle?

Modifying an exhaust baffle can lead to increased noise levels, decreased fuel efficiency, and potentially harm the engine's performance. It can also result in legal consequences if the modification does not comply with local regulations.

5. Is it legal to modify an exhaust baffle?

The legality of modifying an exhaust baffle varies by location. In some areas, it may be illegal to modify the baffle at all, while in others, there may be specific guidelines and restrictions. It is important to research and follow the laws and regulations in your area before making any modifications to your vehicle's exhaust system.

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