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Old 03-13-2010, 06:41 PM   #1
wirewrkr OP
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Inside An Airhead Muffler

I thought someone might appreciate what a 74-84 muffler looks like on the inside. I sliced one today before canning it.
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wirewrkr screwed with this post 12-03-2010 at 10:17 PM
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Old 03-13-2010, 07:37 PM   #2
walkingbear
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Interesting

just looks like a big chamber .. where is the baffle?
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Old 03-13-2010, 08:36 PM   #3
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No wonder they sound like a sewing machine

Cool!
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Old 03-13-2010, 08:41 PM   #4
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Thanks for the tour....I always wondered what went on in there.....quite a restriction at that one point........
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Old 03-13-2010, 08:44 PM   #5
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Wow. That's pretty cool. I've never seen the guts of one of those before.
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Old 03-13-2010, 09:27 PM   #6
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neither had I, hence the picture.
pretty cool huh?
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Old 03-13-2010, 09:56 PM   #7
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I've also wanted to know how they worked! Thanks!

But... now I've got more questions, of course!

So... I see the inlet emptying into the first chamber. Was it meant to exit through just the one hole we see, and the rest of the tubing rusted away?

Then there's a tube connecting the first and third (end cap) chamber.

Now the question: how do the gasses pass from the third back to the second (middle) chamber?

There's a guy in the area here who used to build stainless mufflers - Tom Webb. One of his friends did some research on exhaust technology and came up with the idea that BMW built the mufflers backwards (whatever that means). So Tom built some as directed and with only a slightly throatier note, produced 7 more HP on a 90S in a dyno run. They give the feeling of being in one gear lower.

I've always wondered just what they did to achieve that result. I asked him, but didn't get much of an answer. Perhaps I'll have to have him draw me a diagram.
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Old 03-15-2010, 05:50 PM   #8
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I've been looking at cutaways of mufflers wherever I can find them.

I cannot quite tell the shape of the exhaust path from the front to the back. Is that a simple round tube with another sheet of steel behind it or is it a crecent-shaped tube?

THANKS for the pic.
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Old 03-16-2010, 06:45 AM   #9
Beemerboff
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Snowbum suggests drilling 4 holes in the flat portion right at the rear adjacent to the outlet.

Looking at the slice that would appear to give some gas a straightish path out.

Probably wouldnt free as much gas as a 1/2 inch hole in the main baffle, but it is easier to reverse if it dont work out as planned.
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Old 03-17-2010, 11:17 AM   #10
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Quote:
Originally Posted by Beemerboff
Snowbum suggests drilling 4 holes in the flat portion right at the rear adjacent to the outlet.
My first Beemer was an R60/6 that had this modification. It definitely had a more authoritative sound than other airhead bikes I'd ride with.
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