QUIET EXHAUSTS

[ADEEL MIRZA]

I have a CB750Four K4 with self-fabricated 4-2 exhausts. The exhausts are loud. I wish to dampen the noise to an extent that only engine noise can be heard and no sound comes out of exhausts atleast while idling.

Any suggestions??????

[seestheday]

Get an electric bike?  I'm not trying to be a jerk, but  I don't think I've ever heard a really quiet gas powered motorcycle, unless it was a really small engine.

[ADEEL MIRZA]

Seestheday,

I have previously owned a Magna 750 and a Suzuki GS-550, both with stock exhausts, and both absolutely quiet. Even the new R1s have quiet stock exhausts.

[seestheday]

Ah , fair enough.  We must have different definitions of "quiet".

[ADEEL MIRZA]

So, any suggestions on how to design a, let's say, "quieter" exhaust

[TOOLS1]

Shineyribs has had some experience with making baffles. I'm sure he will chime in soon.
TOOLS

[shinyribs]

Chime in!   I made a muffler for my bike with a stock baffle cut down and wrapped in steel wool.The steel wool made a huge reduction in sound versus just the baffle alone. If your baffles are removable you can try wrapping them in steel wool for better sound absorption. If you are not super cheap like I am you can go to your local bike shop and buy some of the fiberglass packing that is made for re-packing mufflers. That is about all I know you could do to quieten it without sacrificing exhaust flow. Good luck and let us know what worked for you.

Chime out

[ADEEL MIRZA]

Shinyribs, one more query: If I am to fabricate the muffler from scratch, would simple holes in the muffler sheet work. And what should the holes dia be?

[sgtslag]

Here is a great site on how to quiet mufflers down:

http://www.gadgetjq.com/vhbagger_shhh.htm

Take a look at the part detailing welding in of half slugs, as well as the stove pipe rope.  I have not done any of the techniques shown, but I would like to:  my 4-into-4 has a rusted muffler, and I want to keep it 4-into-4, but the slip-on's I have in mind, are quite obnoxiously loud, from the factory -- need to have some baffle work done to make them acceptable.  Let me know if it helps.  Cheers!

[rrgunslinger]

Back in the day we use to drill holes in the bottom of a can that would fit inside the pipe and hold it in with a screw.  Start with a few holes and drill unfilled your happy.  Of course cut the top of the can off.

Harvey

On Mar 14, 2012 9:03 AM, "sgtslag [via Honda CB750&apos;S]" <[hidden email]> wrote:

Here is a great site on how to quiet mufflers down:

http://www.gadgetjq.com/vhbagger_shhh.htm

Take a look at the part detailing welding in half slugs, as well as the stove pipe rope.  Let me know if it helps.  Cheers!

1979 CB750K
1993 Kawasaki Voyager XII

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[LukeM]

Here is a link to my son's CB550F fitted with a stock Sportster muffler.  Compared to the straight pipes he was running, this is much quieter.  Something to consider.

I think that was around 4000-5000rpm when he went by me.  Maybe more.

Luke

[shinyribs]

ADEEL MIRZA wrote

Shinyribs, one more query: If I am to fabricate the muffler from scratch, would simple holes in the muffler sheet work. And what should the holes dia be?

Sorry bud,I cant help you there. I really don't know what I am doing half of the time. I just kinda stick parts together until something works out. Trail and error,ya know. Tools gave me the idea for the steel wool,the other part just happened to work out. Here is what I did.

http://honda-cb750-s.456789.n3.nabble.com/Homemade-muffler-using-stock-parts-td3420689.html#a3827849

[settles]

This might work. http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=SMU17896_0159485103 

[rrgunslinger]

And the HD shops have bunches of them.  If you ask you might get it for free.

Harvey

On Mar 14, 2012 1:46 PM, "LukeM [via Honda CB750&apos;S]" <[hidden email]> wrote:

Here is a link to my son's CB550F fitted with a stock Sportster muffler.  Compared to the straight pipes he was running, this is much quieter.  Something to consider.

I think that was around 4000-5000rpm when he went by me.  Maybe more.

Luke

Back on 2 wheels after a 30+ year break. Used to have a 1979 CB750L, sold it as a parts bike, now riding a 1984 VT700C. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.

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[Cabreco]

My 2 cents:

Back in the 70's I had a 72 CB 500 chopper. It had drag pipes which were INSANELY loud.
I built baffles out of chicken wire & inserted them into the tubes. I was not whisper quiet but you were able to ride with a shorty helmet & still comfortably hear your passenger speak to you.

[LukeM]

What was cool about this project was: I bought a pair of them off of EBay for $20+shipping.  My intent was to put them on my Shadow.  It had had the resonator removed from the pipes. I thought it should be quieter, but never got around to putting them on.  So, my son pipes up and asks for one to put on his bike.  So we did.

I guess if I was going to be efficient about it, I'd find some way to fab up a 2 into 1 exhaust, and hang the one Sportster muffler off of that.  But that seems like too much trouble. Maybe if I get some time and the urge to do it...maybe.

Luke M

[sgtslag]

The only downside to using steel wool, is that it rusts...  Quickly.  That is why they specify using fiberglass.  Fiberglass needs to be made for exhaust systems, though.  Wall insulation fiberglass is not a good substitute.  The steel wool/fiberglass absorbs sound waves, quieting the output.  By adding in baffles, such as the half-slugs welded into the otherwise straight-through pipe, the sound waves bounce around, canceling themselves out as they hit other waves, out of phase.

We test drove a 2009 Gold Wing, three years ago.  No ear plugs, as we did not plan it.  The only sounds we heard at 55 MPH, was the wind.  That was one v-e-r-y quiet bike.  We loved the lack of engine noise, but the wind noise was still loud enough to damage our hearing.  I prefer quiet bikes.  I wish more after-market mufflers were quiet, like the Wing.  Cheers!

[Cabreco]

sgtslag wrote

The only downside to using steel wool, is that it rusts...  Quickly.  

What about using bronze wool. I have used this for flashback arrestors with great luck & they don't rust.

[sgtslag]

Brilliant!  Never knew it existed.  Thanks for sharing!  The fiberglass typically burns a bit, at first -- not sure why, but it is commonly reported.  Fiberglass also burns up, over time.  Does Bronze oxidize (turn green), and crumble, over time, or is that another metal I'm thinking of?

[seestheday]

Errr... I'm pretty sure that the reason the glass packing works is because it physically absorbs the sound waves and transfers it into kinetic energy.  The kinetic waves would cancel each other out to some extent, and the rest would be transferred into the motorcycle, but it's so small you won't notice it because the engine  alone generates much more kinetic movement (vibrations etc).

If it was only in-phase/out-of-phase cancellation then you'd have some coordinates in space that were quiet, but if you moved your head a little bit it would be extremely loud (think of dropping two pebbles into still water and watching the ripples interact with eachother, but mapped into 3-d space).

Now if you'll excuse me, I'm going to put on my pocket protector and go back to my game of dungeons and dragons.