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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.
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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.
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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.
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.
