Exhaust Open exhaust

Discussion in '2-Stroke Engines' started by redpiper777, Oct 24, 2008.

  1. redpiper777

    redpiper777 Member

    Hi I'm working on a board track racer and thought of making a custom exhaust that will carry more toward the rear of the bike...Not much of a muffler, more like an open straight pipe..I know it will be loud but does anyone know the pro's and con's to running an open pipe like this?


  2. fetor56

    fetor56 Guest

    About the only pro i can think of is it will be cheaper.The cons are you'll seize the engine;rather quickly.
    2-strokes are more touchy than 4-strokes but even then they both need that back pressure in order to operate properly.
    Last edited by a moderator: Oct 25, 2008
  3. redpiper777

    redpiper777 Member

    Nuff said, that crazy idea is dead. Thanks
  4. fetor56

    fetor56 Guest

    NP...see what other ppl say cos i'm no exhaust expert but that's my understanding of things(a certain amount of back pressure is absolutely necessary)
  5. Mountainman

    Mountainman Active Member

    wonder where that back pressure video went ?

    yes - especially with the two stroke

    sorry - but - I am not sure where - here on site I saw
    a very cool video explaining importance of back pressure 2-stroke

    ride that thing
  6. jlebh1

    jlebh1 Member

    so how bad would it be to run a 2 stroke without the muffler just strait pipe bent to the style of the frame cause I want to do that to my HT on a stingray type bike
  7. SimpleSimon

    SimpleSimon Active Member

    Not too bad if you can afford to replace the engine every 30 days or so, depending on how much you ride it. Back pressure in the exhaust system is an absolute necessity to running the engine - in its absence you'll burn it up pretty quickly.
  8. macarollo

    macarollo Guest

    On my HT engine one day my baffle flew out... I rode the rest of the day with an open pipe. It was sooooo insanely loud. People everywhere were staring at me. I think on these machines it is best for them to be quiet. Don't want to get a noise pollution ticket.
  9. BSA

    BSA Guest

    Get a Grubee long chrome pipe.
    Youll see them on several websites.

  10. Gungatim

    Gungatim Member

    If you want the look of straight pipe, but still want to have backpressure, take a washer, and grind down the OD to fit inside the pipe. Then just weld it in, either at the end or some place where there's a joint. The washer's ID will restrict the flow some, and create backpressure. If it is not enough, take a piece of smaller diameter pipe with a cap on the end (or just crimp it), weld to the washer, then drill small holes in the pipe to allow some flow of exhaust. Insert the pipe end of the assembly into the pipe and weld the washer end in the pipe as described earlier.

    I did this with a tecumseh 2-stroke and it worked slick, nice sound too!
  11. Mountainman

    Mountainman Active Member

    science ????

    well I think that most will tell us

    there is way more science to it than that

    although up top the mountain -- been known to do things such as this

    ride the motor bike thing
  12. jlebh1

    jlebh1 Member

    what about the exaust that barry makes im pretty sure it has no baffle I might ask him...
  13. Gungatim

    Gungatim Member

    I'm no expert by any means, and I am sure your are correct that there is a science to it, but I have run several 2cycle motors with no exhaust at all with no ill affects. I had solex moped that the exhaust got torn off after it was stolen and recoverd, I rode it for 2 years that way and it never had a problem, also, my scooter project (2 cycle tecumseh) ran with just a 6" piece of straight pipe with no backpressure just fine all summer. Granted, these are not the HT motors, but if you look at the stock exhaust, it wouldn't be too hard to get an equivalent in/out air flow ration with a piece of pipe and washer.

    Any exhaust experts out there care to comment on how to calculate backpressure? I know there's alot of info on calculating tuned expansion chambers, but all I can find (from the 2 stroke tuners handbook) says"outlet pipes should have a diameter .58-.62 times that of the lead in pipe, and the length 12 times the diameter"...if you go too far in restricting the flow, there will be a slight decrease in power and the engine will run hotter.

    I say play around with a few designs and let us know what you find.
  14. biken stins

    biken stins Member

    There was a baffle you could put in pipe and adjust it. Basic washer with a stud mounted. Stud went through a hole drilled in bottom of pipe. Adjustment was just turn a nut then locking it with another. Better acceleration-lower top end when open and opposite when closed. seems like with a control to work it with out stoping might be a way to go. a choke wire control to baffle ?. Anyone try a flame thrower on them yet ?
    Plug in exhaust, wired to switch,wired to white wire ?
  15. jlebh1

    jlebh1 Member

    is this on barrys chopper exhaust?
  16. Gungatim

    Gungatim Member

    That is an interesting concept for an adjustable opening to vary the backpressure. If I get some spare time, I may play around with an exhaust made from pipe, with a T-fitting that I can put a pressure guage on, and a ball valve at the end. Then I could adjust the flow and measure the pressure in the pipe. Be nice to know exactly what amount of backpressure is healthy. Of course, a tuned expansion chamber is best for performance, but not so easy to build.
  17. jlebh1

    jlebh1 Member

    does anyone know if the pipe that barry sells on ebay has a baffle? because if not I can make something very similar at work
  18. Irish John

    Irish John Guest

    I've run my Honda with just the long pipe of the poo poo exhaust and the silencer disconnected. It sounds like a racing bike and it really is a great sound. Very quick throttle response as well. I'd love to ride it occasionally like this but would the lack of back pressure stuff the engine and, if so, how would it cause damage?
    My neighbour thought it was a racing car when he heard the motor.
    Is it the valves that need the backpressure?
  19. jlebh1

    jlebh1 Member

    with a 4 stroke it doesnt matter just look at all the choppers and harleys that just run pipe without a baffle we are talking about 2 stroke engines here
  20. fetor56

    fetor56 Guest

    4-strokes ONLY.

    I doubt if it would stuff the engine.What it would do is cause the gasses to escape quicker...the engine would run leaner & hence hotter.If u want to rejet the carby that problem would be solved.