Exhaust 48cc silencing

Discussion in '2-Stroke Engines' started by jaguar, Apr 14, 2013.

  1. jaguar

    jaguar Well-Known Member

    I believe the 11mm inner diameter of the stinger of the standard muffler is correct for the 69cc, not the 48cc. Dividing 48 by 69, and multiplying it by the cross sectional area of 11mm gives you the area that a 9mm stinger would give. I reduced mine to 8mm to try it out and there was no change in how it ran but the exhaust note was reduced in sound level. So if you have ugly neighbors giving you the evil eye every time you ride by you may want to try this out. 9mm can be had with a 11/32" or 3/8" drill bit drilling into semi-dry JBWeld that was filled in for the last inch of the stinger.

    I regret that people spend good money on expansion chambers that are designed to create a very loud exhaust note. They do that by having the stinger begin at the end of the last cone where the exhaust pulse has been concentrated down to the smallest size so that it has a higher pressure. That high pressure exiting the stinger (or the silencer) creates more noise because of the greater pressure difference between the exiting pulse and the outside air. That is my first gripe. Second is that they reduce mid range power in order to increase top rpm power by means of a steep angled baffle cone, which is a design only beneficial to racer engines with transmissions. Of course you can modify it by welding in a baffle extension and extending the stinger pipe deep into the chamber so that it starts where the belly area is, where the exhaust pulse is the most diffuse with the least amount of pressure. (see more info on my site)

    What a low powered one speed engine needs is an extended intake and an extended exhaust header to give a broad beefy powerband. I have both types of engines and I prefer this type for normal every day use. I dont even have to pedal from a stop with my 48cc. When I lived at high altitude in a hilly city I preferred my 55cc with reed valve and torque pipe for maximum hill climbing power. But still, a 55cc with extended intake and exhaust has more torque taking off from a stop.
    bluegoatwoods and Lee_K like this.

  2. Lee_K

    Lee_K Member

    You are doing some interesting experiments, thanks for that analysis, it makes sense to me.

    So far I have only used 4-stroke engines because they are easier to quite down with simple mufflers. I do like the smaller size of 2-strokes and plan on using one on my next project. I will be building my own exhaust system so i find your analysis to be very helpful.
  3. jaguar

    jaguar Well-Known Member

    Here's a pic of the exhaust lengthened 5" and the 6.5" intake. longexhaust.jpg
  4. determined

    determined Member

    how did you extend your exhaust?
  5. jaguar

    jaguar Well-Known Member

    I found some metal tubing near the same inner diameter, cut it to the right length, and then cut my original tubing a bit back before the silencer, and then had the new tubing welded in place.
    determined likes this.
  6. bluegoatwoods

    bluegoatwoods Well-Known Member

    Let me make sure I understand.

    Is the stinger the pipe where the exhaust exits the muffler?
  7. butre

    butre Well-Known Member

    I don't know why you're so concerned with noise levels. If I'm loud that just increases the probability of a driver knowing I'm there. Quiet is dangerous as far as I'm concerned.

    With my expansion chamber that I modified to be louder, I can take off without pedaling no problem.

    If you live somewhere that's big on noise regulation I can understand but everybody around here rides straight piped harleys or big V8 monstrosities so I'm not exactly making a whole lot more noise than most.
  8. jaguar

    jaguar Well-Known Member

    some people are concerned about noise pollution but it is true that the louder the pipe the safer you are.
    Older people with ringing in the ears need to have silent exhausts to keep from making it worse.
  9. butre

    butre Well-Known Member

    I guess I could see existing hearing damage being an issue. I wear a full face helmet with some padding around the ears and the volume doesn't bother me if I'm not sitting at the top of the rev range. I say go hearing protection before you go quiet.

    Again, the only reason I can think of to actually be quiet is if your area has strict noise regulations or if people might complain about the noise you're making.
    determined likes this.
  10. determined

    determined Member

    I dont wear a helmet , have no kind of lisence yet and live in sacramento .i want to not be noticed as mubh by police. If this means not being noticed by others as much than so be it. I trust my keen awereness .i am greatful for the tips regardless and hopefully i will get everytjing legal soon. Although i do keep hearing about how sacramento police dont trip on these bikes but i think they are just lucky enough so far that the cops had more important things to do
  11. Fabian

    Fabian Well-Known Member

    That's not an explanation people will agree with when you are riding on bicycle trails; with those people who are particularly annoyed by a noisy exhaust being the first people to call the police to have your arse nailed to the wall.
    Secondly a noisy exhaust isn't good for your hearing.
  12. determined

    determined Member

    I totaly agree .and if you cant be safe without being loud then why bother
  13. Fabian

    Fabian Well-Known Member


    Considering that i've now travelled over 55,000 kilometers (34,000 miles) on my bike "with a quiet exhaust" and without any issues caused by a low noise muffler system, the argument for a noisy exhaust has no validity.

    The only thing a noisy exhaust does is to massively irritate those people who are motivated (and have the will and the resources) to do something about getting motorized bicycles banned.
  14. determined

    determined Member

    Wow thats a lot of miles you got under ur belt .and if i can make my bike queiter than i believe the whole community will accept us more.