Author Topic: Quiet this son of a gun down!  (Read 1368 times)

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Offline eigenvector

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Quiet this son of a gun down!
« on: April 15, 2017, 10:43:45 AM »
Riding around today on the Nighthawk, something I noticed (as did everyone within 2 blocks) is how LOUD!!!! it is when the main jets kick in.  <rrrrrrrrrrrrRRRRRRRRRRRR>

The previous owner of the exhaust system (the originals were rusted out Yoshis) took a torch to the mufflers and gutted them totally.
I tried to recreate the original exhaust from pictures online, but since the internal baffles were removed I had little in the way of options.

So I have an open trumpet shell exhaust - my goal is to fit something in there that will effectively quiet the sound.  It doesn't have to be silent, it doesn't even have to be legal - but it does have to be tolerable by people within 2 blocks.
http://i.ebayimg.com/images/g/UjUAAMXQ0pNRulaz/s-l300.jpg

That's an example of the exhaust system.  I still have the end-plates for the mufflers - so I only need to fit something to them, but if I have to I can completely replace them with something else.
Rob
--------------------------------
2018 HD Softail Heritage
1979 CB750K Limited Edition
1977 CB550K
1984 CB700SC Nighthawk
1983 VF750S Sabre

Offline Terry in Australia

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Re: Quiet this son of a gun down!
« Reply #1 on: April 17, 2017, 02:20:02 AM »
Here you go Rob, buy some of these things, (just do an ebay search for "Motorcycle exhaust Baffle") and some fibreglass exhaust wrap, shove it up your............ er, megaphone, screw or rivet it in place, and enjoy your magic carpet ride......... I've done it, and it works perfectly. ;D
I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline eigenvector

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Re: Quiet this son of a gun down!
« Reply #2 on: April 17, 2017, 04:05:02 PM »
I'm an engineer - so I can't just let it go at that.

I have some perforated sheet coming in the mail, I'll make the exit pipe from that - wrap it in baffle material (have some already on hand) then see if that helps out.

I am just not a fan of loud bikes - this one is LOUD!
Rob
--------------------------------
2018 HD Softail Heritage
1979 CB750K Limited Edition
1977 CB550K
1984 CB700SC Nighthawk
1983 VF750S Sabre

Offline Terry in Australia

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Re: Quiet this son of a gun down!
« Reply #3 on: April 17, 2017, 04:15:38 PM »
No worries, I work with Aerospace engineers so I know how they like to turn a simple solution into a major engineering feat for the same result (if they're lucky) so I'll be interested in seeing pics of your solution! Cheers, Terry. ;D
I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline eigenvector

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Re: Quiet this son of a gun down!
« Reply #4 on: April 17, 2017, 04:16:58 PM »
We'll see - this is iteration 2.  First I have to get the material.
Rob
--------------------------------
2018 HD Softail Heritage
1979 CB750K Limited Edition
1977 CB550K
1984 CB700SC Nighthawk
1983 VF750S Sabre

Offline jag767

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Re: Quiet this son of a gun down!
« Reply #5 on: April 18, 2017, 02:01:51 AM »
I'm an engineer - so I can't just let it go at that.

I have some perforated sheet coming in the mail, I'll make the exit pipe from that - wrap it in baffle material (have some already on hand) then see if that helps out.

I am just not a fan of loud bikes - this one is LOUD!

I just picked up a ducati m750 that is like that. With straight pipes, it's so unnerving that riding it home I pulled the clutch in if I even thought I saw a cop! When the guy selling it to me started it I actually jumped not expecting that amount of noise.

Offline Terry in Australia

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Re: Quiet this son of a gun down!
« Reply #6 on: April 18, 2017, 04:33:24 AM »
Loud pipes save lives! (if not eardrums, and relationships with neighbors........ ) ;D
I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Online Don R

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Re: Quiet this son of a gun down!
« Reply #7 on: April 18, 2017, 10:05:07 PM »
 I enjoyed making the baffles for the 76F mufflers. Let your imagination be your guide.
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline eigenvector

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Re: Quiet this son of a gun down!
« Reply #8 on: April 20, 2017, 05:21:32 PM »
Well....

I think I made it louder   ;D

7" of 1/8" perforated aluminum plate wrapped in coarse stainless steel wool.  It's better than what was there originally - nothing.

Trouble is I only have 7" to work with - there's a diffuser plate welded into the muffler can 8" into the body.  With only 7" to work with there isn't a lot of room for the exhaust air to expand and diffuse within the muffler.

If this fails - I'll try a design that forces the exhaust to change directions before exiting.
Rob
--------------------------------
2018 HD Softail Heritage
1979 CB750K Limited Edition
1977 CB550K
1984 CB700SC Nighthawk
1983 VF750S Sabre

Offline Terry in Australia

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Re: Quiet this son of a gun down!
« Reply #9 on: April 20, 2017, 06:09:50 PM »
7 inches is always enough mate! But seriously, depending on the OD of your muffler, 7 inches of baffling should be fine, I had to do it on my CX500 Custom when I installed some excellent looking (but pretty much unbaffled) stainless steel megaphones and I don't reckon I had 7 inches of space to fill with quality fibreglass baffle material (even stainless steel wool isn't great, it's not packed tight enough) and I ended up with a nice mellow sound that passed a roadworthy certificate inspection. Cheers, Terry. ;D
I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline eigenvector

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Re: Quiet this son of a gun down!
« Reply #10 on: April 21, 2017, 04:37:36 PM »
Okay, so I took it out today after work and it's better.

Sounds as loud as any aftermarket sport bike pipes, the high-end sound is quieter, but the low end sound is a bit higher.  All in all it evened out the volume.

I'll stop farting around with the pipes for now - this bike won't get out enough to bother the neighbors.  It still needs a lot of TLC.
Rob
--------------------------------
2018 HD Softail Heritage
1979 CB750K Limited Edition
1977 CB550K
1984 CB700SC Nighthawk
1983 VF750S Sabre