Exhaust no muffler on a 2 stroke?

Discussion in '2-Stroke Engines' started by motorpsycho, Aug 9, 2009.

  1. motorpsycho

    motorpsycho Active Member

    i know that you can gain a bit of power by letting the exhaust breathe better. (as well as letting the intake breathe better too)but, how much exhaust backpressure do these little 2 strokes require in order for them to run "right"?
    i'm wanting to ditch the stock muffler because it seems so restrictive. i want to run a long straightpipe without the muffler instead. would loosing the muffler affect low end power that much?
    i know it'll be loud, but that's ok....i like loud.

  2. biken stins

    biken stins Member

    engine will last longer with a baffel also will add to top speed.
    Straight pipe lowers top speed,bike is quicker.
  3. Mountainman

    Mountainman Active Member

    good advice from stins there

    good advice from stins

    have never seen using a straight pipe on a 2-stroke to be a good THING

    they sure do sound good on a Honda 90 though !!!

    as we ride those THINGS
  4. customcruiser

    customcruiser Member

    ive run no exhaust on my bmx tijuana 66cc and skate board i noticed a 20percent increase in accelaration and speed but loudness i cant hear ppl talking after a 2hour ride and makes fuel economy abit worse but i want power my boards engine completely fell off at 40kmh and i fell off in the middle of the road cars were comin along at 60kph and were 80meters from me so ive replaced the 32cc with a 49cc pocket bike engine i had shud get more power now still gotta make a chain idler for it tomoz

    Attached Files:

  5. AussieJester

    AussieJester Member

    20% WoW and what method was used to get this figure? seeing the baffles on two strokes actually ad to performnce and all... :whistling:
    Playing with expantion chamber size baffle/stinger length is where the HP comes from in two strokes not remvoing them
    Last edited: Aug 10, 2009
  6. Bikewer

    Bikewer New Member

    Two stroke exhaust tuning can be complex. Racing engines with tuned expansion chambers are set up so that the exhaust provides a "resonant pulse" back to the still-open
    exhaust port to keep the incoming charge of air/fuel in the combustion chamber.

    Engines set up with simplified exhausts tend to have more low-end torque; this was standard on "trials" motorcycles for many years.
    It's mostly trial and error for the home builder who doesn't have access to fancy measuring devices.
    Nate888 likes this.
  7. nadroj

    nadroj Member

    if you want to run just a straight pipe you will be fine.
  8. nadroj

    nadroj Member

    that is only if it has an expansion chamber, if the exhaust is just a mufler anything would be better than that
  9. graucho

    graucho Active Member

    With the cheap finicky nature of the HT engine I think air flow and back pressure too far "out of the norm" would result in a big KA-BOOM! after a few hundred miles. Im not talking all 2 strokes, just the HT engine. Yet im all for experimentation, at the price of these engines.....go for it and report back.
    Last edited: Aug 10, 2009
  10. wheelbender6

    wheelbender6 Well-Known Member

    Straight pipes are not very neighborly.
  11. nadroj

    nadroj Member

    I disagree, because they are so out of norm I think they will run with almost any exhaust.
  12. graucho

    graucho Active Member

    Maybe you rite, maybe wrong. Thats why I want him to test it on "HIS" engine and get back to us.:grin5:
  13. SimpleSimon

    SimpleSimon Active Member

    One mans music is another mans noise.

    I truly despise the sound of a screaming 2-stroke engine un-muffled. It is provocative noise like that that results in shovels to the chest, or black rope across the road 18 inches above the pavement, or other such misbehaviors.

    You might love the sound - odds are everyone around you wishes that engine would blow up.
  14. motorpsycho

    motorpsycho Active Member

    well, where i live neighbors are not a concern. i don't plan on riding in the city...this is just for fun. but, i have been doing some research and i am more in favor of leaving the muffler / baffle on it and just extending the pipe. i just want to get the pipe routed out from under the frame. it looks so incomplete just hanging there like it is (since my motor is in a 20" frame, the muffler ends right in the center of the cranks on the underside of the frame)
    i am all into customizing stuff, and i want to make a new exhaust...i just thought it would be easier to just take the muffler out of the equation.
    but, now my thought is to put the muffler at the end of the pipe instead. i have messed with 2 stroke dirtbikes with expansion chambers and all that and i have an idea of how an expansion chamber works. i just wasn't sure on the backpressure needs of these little motors.
  15. customcruiser

    customcruiser Member

    nor am i my good friend nor am i.....i have now run my bike for 100km and my board about 40km but am getting a pocket bike expansion pipe and hacking it to fit replaced my boards engine with a 49cc over the 32cc has more grunt now
  16. Mountainman

    Mountainman Active Member

    oh well -- here I go -- get on that coffee

    yes the coffe is kicking in now

    let's just say that if we all ran straight pipes for just one day
    it would probably mean the end to motorized bike riding as we know it !!!

    yes I have ran straight pipes on many THINGS for many years
    just sold a Ford Escourt a short while back -- straight pipe for years
    sounder like a Ferris
    I seem to know when to hold it down
    like through town and in our neiobhborhood so as not to bother people

    have seen many going by with straight pipes
    such as used on scooters
    I hate those THINGS
    and yes
    I would vote them out of here in a minute

    it's all about how we ride those THINGS
  17. motorpsycho

    motorpsycho Active Member

    I just have to say that i'm 40 years old, and i have always been a "striaght-pipe" kind of guy. i have owned drag cars with open headers, i currently own a custom 55 pontiac with dual straightpipes and no mufflers, i also own a 66 triumph bonneville with straight drag pipes on it. needless to say, i like the noise.
    but, on this bike, i'll keep it quiet so it isn't so annoying. there is a difference between having a good sounding loud exhaust and an annoying loud exhaust.
  18. SimpleSimon

    SimpleSimon Active Member

    Last year there was a young cop here in town who made a habit of sitting at the light right outside my apartment on his Suzuke with the straight pipes, and revving his engine (at 2:15 a.m.) while waiting for the light to change, then accelerating as fast as it was able up the street. My neighbor, a 71 yr old retired AF colonel, backed out to take his wife to hospital at the wrong moment - as the light changed - and the cop broadsided their car. According to the damage estimator, in half a city block he had gotten to around 50 mph (in a 35 zone).

    Accident was ruled to be the cops fault due to excessive acceleration and speed. All I know is, that screaming ricer isn't waking me up at 2:15 am anymore. I feel sorry for the young cop, as he will never walk again, and has significant brain damage, but I am glad that screaming bike is silenced.
  19. icyuod2

    icyuod2 Member

    i would love to mount an exaust to my boardtracker, similar to the one on this twin cylinder indian pictured in this vid. ( def. worth watching him start them up) theres something very cool about shooting flames out the side of your ride.lol :)

    could a similar exaust be put on my chinese motor? if so what would be the result? (more/less power, longer/shorter life span etc)
    what is it about these old indian engines that allows them to run such little pipes? that single cylinder indian barely has a 2" long exaust.
    Last edited: Aug 12, 2009
  20. biken stins

    biken stins Member

    Has anyone used the white wire to a spark plug neat the exhaust end ?
    Good ol 50's flame thrower.
    Hmmm. There may be hope for the white wire yet.
    built_not_bought likes this.