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  • Amplifying Exhaust Sound

    My nephew is into building his first go cart. It has a 12 hp briggs motor. He wants to know how to make it sound really tough and loud. I'm not really for the noise but it will be a learning experience for him. I figured a straight pipe would be loud enough but I'm sure someone has some info on building an expansion pipe for this. Any help will be appreciated.

    JL........................

  • #2
    Tell him to go to any of the Honda automotive forums or visit a tuner shop.

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    • #3
      Just look at a harley. -_-

      But seriously, I think the peak of mechanical engineering is producing as much HP as you can, as QUIETLY as you can. I cheer when I hear bikes pass me purring like a tiger. I boo when I hear em roar past like some defective dying elephant.

      Expansion exhausts are for 2 strokes, Not 4 strokes btw. A 'megaphone' exhaust is probley best for a 4 stroke... But seriously. Use a muffler. Even just a glass pack or similar will GREATLY reduce noise without reducing HP.
      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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      • #4
        Its a single cylinder, you cant make it sound tough. Just loud which will be sure to piss off anyone around if you live in a populated area and draw the wrong kind of attention.

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        • #5
          Its a single cylinder, you cant make it sound tough
          I don't agree. Bikes with large singles sound pretty good. Mine used to draw a lot of attention when I cruised by at maybe 600 rpm. A very solid Thump 300 times per minute. For a small engine it won't be nearly so interesting sounding and you can't put on a long enough pipe to make it sound good. It's easy enough to try but it will need around 4 to 6 feet of pipe.

          It will also do a good job of annoying the neighbours.
          Free software for calculating bolt circles and similar: Click Here

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          • #6
            Route a straight pipe that exits right behind the seat at head level.

            At least it will be tough and loud to the driver....

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            • #7
              Originally posted by Evan
              I don't agree. Bikes with large singles sound pretty good. Mine used to draw a lot of attention when I cruised by at maybe 600 rpm. A very solid Thump 300 times per minute. For a small engine it won't be nearly so interesting sounding and you can't put on a long enough pipe to make it sound good. It's easy enough to try but it will need around 4 to 6 feet of pipe.

              It will also do a good job of annoying the neighbours.
              Brass instruments have solved the problem of getting a pipe long enough into a compact space. Maybe he should ask Hornluv for advice.
              .
              "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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              • #8
                if you could figure out a way to pinch the exhaust like a trombone player pinches his lips..then youre half way there ..but you wont have any power.

                how about running a siren with the exhaust ..be like a Messerschmidt then (not the bubble car ..the plane) :0 ....and that's the evilest sound on earth

                all the best.markj

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                • #9
                  Originally posted by Evan
                  I don't agree. Bikes with large singles sound pretty good. Mine used to draw a lot of attention when I cruised by at maybe 600 rpm. A very solid Thump 300 times per minute. For a small engine it won't be nearly so interesting sounding and you can't put on a long enough pipe to make it sound good. It's easy enough to try but it will need around 4 to 6 feet of pipe.

                  It will also do a good job of annoying the neighbours.
                  I should really get a recording of my 2 stroke bike. While cold and 4 stroking, it sounds like ****, with poping noises and such.

                  However, once it warms up, And you put the engine under load (say 1/4 throttle or higher, either accelerating, or boging the motor down in a high gear), It puts out a very nice purring tone and the poping goes compleatly away. Its exhaust length is only about 3' total, maybe a little less. Has 5" of fiberglass pack at the end, with an expansion chamber just before that and another 16" header pipe.

                  At full throttle and/or high rpms it maintains the same sound till redline, But gets much louder Crusing however its very quiet, Especialy at lower speeds in higher gears, so the engine is very boged down (Little over idle RPM but throttle about half open), If you let the engine get unloaded, it goes back to 4 stroking.. Nature of the beast. Thankfuly theres a free wheel in my bikes drive train, So I can go beween accelerating with a bogged down motor and idleing at low RPM in 'neutral' by just twisting the throttle, and idle is pertty quiet dispite the 4 stroking once its warm.

                  Very, very good acceleration, expansion exhausts with 2 strokes improve power *and* reduce noise, as the energy of the sound pulses gets reflected back into the motor and idealy, dampened/traped by the motor.

                  Also modifyed the expansion chamber to have a stinger pipe that goes several inchs into the expansion chamber to have its inlet be the widest point in the expansion chamber, theory being thats where the pulse is at its weakest. You don't want the pulse going out the exhaust, Just the bulk exhaust gas flow. This seemed to have improved power and reduced noise by about 20% just by itself.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                  • #10
                    A megaphone exhaust would make it about as loud as can be. Just a simple cone. You might get a more pleasingly hollow tone from it with a reverse-cone on the end but it will be less loud. A cylindrical can with quite a large outlet will also give a tone more like a sporty engine than the Briggs but there's not a whole lot more you can do because the Briggs is tuned lazily for long service.
                    Peter - novice home machinist, modern motorcycle enthusiast.

                    Denford Viceroy 280 Synchro (11 x 24)
                    Herbert 0V adapted to R8 by 'Sir John'.
                    Monarch 10EE 1942

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                    • #11
                      Changing the exhaust on a motor like that could possibly cause a melted piston. They are already jetted to the lean side, opening the exhaust will only make it worse.

                      At the least it will suffer a loss in power.
                      Gene

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                      • #12
                        Swat him upside the head. He needs different heros and standards. He need to know that a noisy entrance image is a loser's ambition. Success is the primary attribute of cool. Quiet is cool.
                        Last edited by Forrest Addy; 07-06-2011, 05:11 PM.

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                        • #13
                          If he wants a deeper more car like tone, here's something I discovered by accident.

                          I was doing some testing of a cart motor on a dyno stand out behind my shop but the noise was starting to bug neighbors.

                          I got the brainstorm to quiet it down by putting an auto muffler on it. I didn't want any restriction so I got a 2-1/2" in and out sized "turbo" muffler, around $25 bucks or so from summitracing.com (commonly used on V8 dual exhaust systems) and adapted it to the pipe for the motor.

                          Surprisingly this made the noise worse. Instead of "pop pop pop pop" I now got "boom boom boom boom", a much deeper more resonant tone, probably overall less actual sound level than the pops but it now sounded like a much bigger and nastier engine was being run wide open behind my shop.

                          I had to take it off, it made it sound like I was running a much bigger engine than a cart engine.

                          Paul T.
                          www.power-t.com

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                          • #14
                            As always, Forrest has nailed it.

                            Plus Topct is likely right about messing up the air fuel ratio.

                            Steve

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                            • #15
                              I seem to recall an old thread where we were told that plugging the exhaust off and drilling an 1/8 inch hole for the exhaust was the way to go...

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