h a l f b a k e r y
Not so much a thought experiment as a single neuron misfire.
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When trying to get the cycle home at 2 or 3 am you want to be as quiet as possible (whether to not irritate neighbors or so significant other doesn't wake up and check clock). However you might not exactly want a quiet cycle the rest of the time, like when riding with friends.
I suggest that the
baffles inside the exhaust pipes be put on a central swivel, rather like a Venetian blind, then hooked to an electrically activated two position solenoid that allows you to specify the baffles up or down.
When wanting to feel the kick and hear the rumble you open the exhaust flow up ( baffles down) and when you need to be quiet you choke the flow (baffles up).
Although severe restriction of flow would cause some degradation in performance, that isn't something you worry about when coming home late, or leaving early for that matter. Also, with more bikes being fuel injected the fuel commander modules can often adjust performance quite a lot to match sensor data on performance.
This would also be very, very good for those of us who live in areas where the police might take a dim view of louder bikes. Just imagine being able to say," Really officer? You must have been imagining things, here we are standing right next to the running bike and as you can tell there are no noise level violations occurring."
Powered Exhaust Bypass
For a Mustang, but I'm sure the concept translates. [Klaatu, Oct 04 2004]
Exhaust Bypass Kit for Kawasaki - warning - small .pdf file [Klaatu, Oct 04 2004]
Exhaust Control Valve
"System includes a cable-controlled plate that can be adjusted from fully open to fully closed..." Again, designed for an automobile, but I'm sure an enterprising engineer could mock something up. [phoenix, Oct 04 2004]
DB Killer - Removable Baffle
'Decibel Killers' or removable baffles are available for many exhausts, though all require some manual intervention to remove currently, unlike the mechanised system described here. Many bikes are fitted with variable exhaust valves (eg Yamaha's EXUP) but this is primarily designed to affect gas flow, not sound levels [exhaust-notes, May 16 2008]
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||I believe this may be baked. Exhaust bypass kits have been available for many years. You can put extra fiberglass in your exhaust for late night driving and during the daylight, bypass them.
||Klaatu - those are not what I am talking about exactly, but good links in that direction. I know what header cutouts (first link) are and they are not going to allow some baffling to still be there (without going through a second set of mufflers which is what we are trying to avoid). Weight counts on bikes alot.
The second link is to a manufacturer of a work around to a particularly disturbing piece of Kawi engineering. This doesn't address the issue in my opinion either, although the header cutouts do come closest.
Actually most baffles are adjustable now, however I personally would not want to try unscrewing the baffle shell, removing or adding fiberglass, and cutting off / welding on extra baffle length while driving down the road.
What I am suggesting is something very simple to adjust on the fly that would still leave some back pressure when loud and reduce noise volume when needed.
||I once bought a pack of steel pot scourers and poked them inside the mufflers of my bike to pass the annual inspection. Cheaper than new mufflers and to remove simply rev the freckle out of the bike as you ride away from the testing station and watch the scourers burn...
||UnaBubba - if you can catch him you can run him over. The only rule for this hunting season is you can't get him at a stop light. Got to make it fair you know.
Course we are allowed to defend ourselves, you have to follow us on the roads and at the speeds we choose!
||When I was shopping for a can for my bike, I went the preformance route. But I don't have a significant other to make angry. Currently I have a dear friend that frequents the dragstrip on his bike, and simply removes some of the fiberglass packing for that application. There are a few silencer companies make their mufflers servicable. A few allen bolts, and you can add as much or as little fiberglass packing material as you'd like. Older Vance&Hines systems did this.
||'fort - I agree they are adjustable, but not on the fly. That is the point of this excerise. Rememberthat we want to make it louder or quieter while riding and without carrying tools and supplies.
||I understand what you are suggesting with your idea, but I personally don't mind turning a wrench for a minute, and adding some packing ... lord knows, it weighs only a few ounces for a full package.
||Exaust bypass systems for preformance are baked. When you want it quiet, you simply switch it back to the baffles, and you're set ... One setting for the neighborhoods, and one for the highway; and the bypasses are just that. Also, I would like to bring up the preformance factor of this idea. For a genuinely good preforming sportbike exaust (for example) Yoshimura full kits retail for close to 2 grand, and its track/dyno tested for the bike that its built for. That means a healthy balance of backpressure, proper carb jetting, or injector mapping, etc. However, Carburetors can't be easily adjusted on the fly. Which may end-up causing damage to your piston rings or valves. Tieing it all together would be costly and complex. Try taking it slow through the residentials to keep the noise down. If your bike is that loud WITH a silencer, try investing in a more effective silencer.