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Rather than edit that rambling I'll add more here... Another reference point or two. My 851 is more or less (ok, more more than less) two of your engines in one. Each cylinder is roughly the same size as yours. To quiet that bike down it's got two mufflers, each 16" long, with 1 7/8" cores. But the outer diameter is about 2" bigger than the inner so it's got roughly 1" of fiberglass packing over 16" of two mufflers to quiet it down. I say two mufflers because there's a crossover between the two sides - each cylinder breathes through both mufflers. That helps quiet things down too, along with the flow dynamics of two cylinders working with each other. But I digress...

As for frequencies... you might think that it would be twice the frequency of yours but it's not because it's a 90 degree V-twin (save me the "L-twin" marketing bullshit Ducati fans, mathematically it's a 90 degree V). The 90 degree offest with the single crank pin makes the fundemental frequency an odd order which basically introduces fractions into the mix. That adds it's own complications when using reflective tuning but it's moot since it's now got glasspacks on it just like every other '90s Ducati.

ANYWHOS... long story short, an 850cc V-twin with mufflers larger than yours will still set off car alarms when you let off the throttle, so you've got your work cut out for you making the shorty megaphone quiet.

These mufflers are actually small in modern terms.


Here's a more modern V-twin (Edit: But still nearing 20 years old). Each cylinder is about 500cc, glasspacks again. This bike has two of these on it to quiet it down. Ya want quiet with low restriction, ya gotta go big.


If I were you, and I wanted to use a small megaphone, I'd search on dB killers and find something that looks like honeycomb foil in a tube. Install that upstream of the muffler and see how it sounds. Then go to the trouble if rebuilding the muffler if it's still obnoxiously loud.

And/or bite the bullet and get a bigger muffler to start with.
 

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Just to clarify something. If you can't find a db killer and have to modify teh internals of that muffler, what you want is a smaller diameter long perforated tube - not a cone. I'd suggest the diameter of the header or one size smaller and they are available on ebay or a few other shops.

But let's all hope that isn't needed. When you drill out the rivets and show us what's inside we can advise you better what to do next.
 

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if you can drill the rivets out and get inside it you could weld something to whatever is in there (assuming it's not a real megaphone, which is empty and a tuned chamber like a 2 stroke expansion chamber) that allows you to fit and remove a baffle from down inside. i'd make a baffle that obstructs the flow - so you can't see through it. it's only a 400 so shouldn't need a heap of flow, and it has a fair bit of down time flow wise.
 

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looks just like a cat. maybe the high flowing for required restriction design works well. the small holes would work well to stop the low frequencies? and the length would also help - a passage instead of just a hole in a plate?
 

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Discussion Starter #26
All..thanks to everyone that has replied. You've given me a lot of helpful information! Attached are some pictures of the inside of the exhaust. It looks like it's a straight through shot from end-to-end. It looks like the inside material has some texture to it but it doesn't have holes/mesh (it's more ribbed).

I wanted to check back with all of you before removing the rivets. Does it look like I can make modifications to what I've got to make my exhaust more quiet? Or, am I SOL and should I bite the bullet and get another exhaust.

103830


103831
 

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looks like a perforated tube core, which is what you want.

i'd say it depends on how much the amount of money it's going to cost you to replace it should you fuck it means to you. i'd get the drill, worry about that hindsight shit later.
 

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I just wanted to thank the contributors to this discussion for providing both a practical and theoretical response to this post. I certainly learned something.
 

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You've chose a great canvas to paint. There are quite a few companies out there that do SR4-500 stuff. I had a 500 in my youth that I reqlly enjoyed, until I got myself a GF that enjoyed riding with me and suddenly I needed a bigger bike...

Anyway, Do you live in California? That's the only state that I know of that requires the exhaust contain a catalyst.

That said, I've done the reverse cone thing on an Enfield single. Loved the tone, couldn't make it comfortably quiet.

Excuse the commentary...


It was much louder than it sounds in this clip. I tried more glass packing, I tried stainless steel packing, I even tried adding a second perforated tube. It had to go...

So, on my current single, I went to a Goldstar type silencer and love it.


Much quiter than represented in this clip. Such is the issues with indoor and outdoor recording...

I'll suggest using a similar pipe in your case, because as mentioned in another post, more volume, the better potential for quieter operation.

PLUS, SRs make really nice looking roadsters dressed up as goldies.

 
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