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Old 06-20-2010, 09:45 AM
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Building a performance muffler

I posted this on several motorcycle web sites and no one can help so I'm turning to the experts here.

I have a new 2009 Buell XB12XT. I plan on installing the race ecm sometime soon. I'll install the race muffler also when it becomes available. In the mean time I bought a near new extra muffler to mod. My goal is to have a better sounding bike without excessive noise. I first cut it apart and remover the 3 pipes and bulkheads.



I'll leave the interactive valve in place to give the muffler a stock appearance. The valve it is fully open at idle and at high power. It's closed mid range to increase torque. When it's close it routs the exhaust trough the smaller pipe to increase back pressure.



The problem is it's too quite, it sounds like a sewing machine. What I want is a good free flowing exhaust that's not too loud.



I'm installing 3 baffles, the 2" holes will be staggered. 2 will be welded at the jack points and one in the middle.



I have a lot of hot rod experience and I'm kind of copying a Flowmaster 3 chamber muffler, not too loud and not too quite. Before I weld everything up, I'd like to know if I'm on track. Any suggestions?

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Old 06-21-2010, 08:34 AM
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not an expert

In the mid 90's I worked for the Co that made OEM harley and Buell mufflers. AT the Bike shows the harley engineers used to show the new stuff and talk about the developement process. and let you know what to do, EG. " at first we tried using these size holes, and had to change jetting , we had this much more power but did not meet sound level specifications , we next tried this and had this much increase in torque at this speed but did not meet sound regs. ETc .Big Brother regulations about modifying vehicles and using non approved parts.
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Old 06-21-2010, 11:11 AM
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a 3 chamber flowmaster doesn't work anything like that... generally they have a first chamber that uses resonant tuning to cancel and enhance some frequencies (like a ported speaker box), a middle chamber that splits and recombines the flow hoping that the split flow coming back together again will again, cancel some other frequencies and then finally a baffle something like you have.

For the most part they end up pretty restrictive, I know that many of them actually end up flowing less and hurting HP numbers vs modern OEM muffler designs.

I've experimented with my own mufflers before and will suggest that what to do depends on what you want it to sound like. Baffles tend to quiet things overall and attenuate lower frequencies, packing tends to attenuate higher frequencies (2 ways, it absorbs the higher frequencies, and also makes the sound travel slower through it which makes the muffler act like a larger chamber tuned to resonate at a lower frequency, and as that goes lower it generally it gets quieter, just like a smaller sub box hits harder but at a higher frequency also).

Generally I hate raspy sounding exhausts but like a nice, low muscle car burble if that makes sense, and one thing that I have noted is that the more hard, straight edges you have the more metallic/raspy things tend to sound (I generally don't like most of the flowmasters, but the super 40's sound good on some cars).

One design that I've had really good luck with is taking 2 tubes the size of the inlet and outlet I need, drilling a bunch of holes in their sides (say 2" holes in 2.5 or 3" pipe, maybe 3-4), facing them at each other and enclosing them in a box. I had something like that (but with an outlet coming out both ends to make a crossflow design for my '97 TA) that my neighbor, not really a car guy (meaning if it was obnoxious he probably would have hated it) absolutely loved the sound of, and walked across the street to tell me that a few times. It got rid of the sort of nasty, disorganized sound that LT1's have without a muffler, reasonably quiet at idle aggressive (but mostly lower frequencies) at open throttle, no popping, rasping or any bad traits. If it was too loud the plan was to perforate the housing and wrap it in glass wool and build a larger box around it, but I didn't find that necessary.

It was also the only exhaust on that car that I wasn't able to document a loss at the track with against the stock muffler (people have documented an 18-25hp loss swapping the stock for flowmaster on those cars).
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Old 06-21-2010, 11:05 PM
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This is what I've come up with. The blue lines are the baffles. Will it be too loud? I'm not sure. I do know that most guys simply gut the muffler. The baffles are welded in and I'll finish it up tomorrow. What do you think of my design?

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Old 06-22-2010, 08:22 PM
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I'd skip the diagonal baffle or put it going the other way, I'd also make the holes in the baffles slightly larger than the inlet and outlet. If you want to duplicate what flowmaster does then make the baffle V shaped with the point down and possibly add one or 2 smaller V shaped baffles in front of it with the point facing up.

The flow director after the second baffle is a good idea.
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