Ultra quiet 70 CC?

Discussion in 'Performance Mods' started by andyinchville1, Aug 16, 2007.

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  1. Just wondering, but if a person were to weld a steel pipe to the outlet of the
    factory exhaust and route it into a small car muffler would the result be a
    motor bike that is as quiet as a car?.....I thought it might be neat to be super stealthy!.....I do recall that there was mention that the intake may also be a source of noise and was thinking the same basic idea could be employed there too....but since the carb is close to the frame anyway it may be necessary to make a custom intake so that an intake silencer can be employed.....Anybody out there try anything along these lines?

  2. azbill

    azbill Active Member

    I think it would cause to much back pressure and be detrimental to power:confused:
    my chopper had a lot more 'git-up-n-go', when I cracked the long exhaust and switched to the stock one
    the long pipe was quieter, but the short one made a BIG difference :D
  3. I was thinking that because I would be using a car sized muffler that there would be no significant back pressure since it would originally be designed for a large V8.....I was hoping this would give noise reduction without loss of performance....well, except for maybe the weight factor...
  4. davidsis

    davidsis Guest

    Car muffler

    sounds like it might work
  5. rcjunkie

    rcjunkie Guest

    It would be quiet but ugly. No worry w/ backpressure since the car muffler is designed to accept 4+ more flow than a 1 cylinder engine.
  6. Patch

    Patch Guest

    Well with less backpressure...I believe the muffler would be more like a resonator. Ya know, like a real tingy pop pinging sound from the muffler. But that is a good idea. hows about a dirtbike or and FMF atv muffler those are very muffled even when you drop them on the floor. just watch the backpressure. So i think a large atv FMF silencer would work always wanted one on my gokart but they're pretty pricey!!!
  7. motoschwinn

    motoschwinn Guest

    Well how quiet is the POO POO pipe? I need to find something too, and there is a go-cart shop, that I was looking at having them make me a quieter exhaust system....
  8. motoschwinn

    motoschwinn Guest

    Plus I get lots of noise from the clutch side of the motor, when I press my fat old leg up against the cover it cuts out most of the noise... I was thinking of some kind of rubber covering, but it seems to be really hot. Performance for me is not the issue, I just want to run as quiet as possible.
  9. I am guessing that the poo poo pipe is muffles like the pipe than comes standard with kits from Dax / Kings etc....I think the pipe just looks different because if the longer tubes...so with that I would assume that there would not be a significant difference in sound level (increase or decrease) ...Others may jump in if they have first hand knowledge of this tho.....The mufflers on lawn mowers... say for in stance the Kohler 25 HP engine....are somewhat larger but still do not muffle very well,....I hate to say it but I think for supreme quiet without unnecessary power robbing back pressure, a good car muffler would be hard to beat....If I weren't so busy I would experiment this weekend but lately work has kept me hoppin!

    PS - Don't forget I have heard others say that the intake is noisy as well BUT I think most of it is the exhaust myself....There are also some people that believe that noise radiates from the cylinder cooling fins....I have seen some people wedge runner tubing in strategic locations on the cylinder heads to keep the harmonics down...I assume that this was done AFTER the majority ofthe noise was address by taking care of the exhaust and intake noise.
  10. Alaskavan

    Alaskavan Guest

    So, has anyone come up with a way to make one of those 70cc's quiet? I've been thinking a bit about stealth. Wouldn't it be cool if I could build something where it would take very close inspection to see/hear there was a motor involved. I know this is not practical on a 2 wheeler (I'm thinking beyond the milk crate on the rack mount), and it may be anathema to the serious gear heads, but still.... Whisper quiet is what I'd like.
    Last edited by a moderator: Sep 7, 2007
  11. I agree with alaskavan....it would be really neat to be stealthy on a cruiser type bike and blow by some really hard core bicyclists (the ones that look like they belong in the Tour De France)....Like Mr. Bean or Pee Wee passing all those decked out racers...that would be too funny!....I am actually going to try the car muffler
    idea when my work slows down and I get some free time
  12. Has anyone tried putting fiberglass muffler packing into the muffler to quiet it down? I know that's what they do for 2 stroke dirt bikes.
  13. gauge

    gauge Guest

    i was thinking the ame thing at school today while the teacher was boring me mr vanderhoof , if i pack the muffler withh fiberclass packing it may quieter her down to be alittle more steathy to sneak up on people
  14. I think packing our mufflers with fiberglass would cause undue back pressure....the "cherry Bomb" glass packs for automotive use is a straight through design with louvers and then the area outside the straight through pipe is packed with fiberglass...If you try it, definitely post your findings...

  15. Alaskavan

    Alaskavan Guest

    I don't recall the cherry bombs being particularly quiet. At least not on my hotrod.
  16. Dockspa1

    Dockspa1 Guest

    2 strokes require a little back pressure to run right. I remember when I was young playing with the dinosaurs, I had an old sears 250 with the baffles. I thought it would scream if I took them out. Man was I wrong. It had absolutely no power band. Low or High. They went back in pronto.
    Here is a good question that maybe someone here knows the answer too.
    Are the pipes that go on the 48cc the same as the ones that go on the 70cc.
    They probably are due to the cheapie Happy Time traditions.
    One is either too big or too small for the proper balance.
    Maybe just a 1/4 " hole drilled in the 70cc would help to balance it?
    Any thoughts or facts?
  17. I picked up some 2 stroke silencer packing at the local shop. It was easy to put in. I just undid the screws at the end of the exhaust pipe and pulled out the pipe. Mine was drilled full of holes and pinched in the middle by the people that I bought the kit from. I went ahead and wrapped it with the packing, put it back in, and took the bike for a test run. The response on the throttle was a bit sluggish. The HP was still there though it just took a little longer to pick up. The noise reduction was HUGE though, and I mean HUGE. It was really freakin' quiet. The squeal that the clutch gears make is the loudest sound that my bike makes now.

    I'm gonna try taking a blowtorch and monkey wrench to the pipe and take the pinch out of the middle and see how that affects the sound and torque. I'll try and post some pics too.
  18. Alaskavan

    Alaskavan Guest

    Yes. Pics and more detail please.
  19. So I just took the bike for another test run and I have to say that the torque just isn't there when I'm going up hills. I think that the reason for this is that my pipe was pinched at the center by the person who sold me the kit. Here are a few pics. I haven't been able to heat the pipe and force it back to a circle in the center with a blowtorch and pliers. What I'm thinking is that I should drill a hole or two in through the pinch to open it up.

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  20. Here's another couple of pics. I'm thinking about wrapping only part of the pipe. That way there is still some room for compression.

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