Exhaust Jag pipe on 66cc

Discussion in '2-Stroke Engines' started by wagel, Oct 6, 2016.

  1. zippinaround

    zippinaround Active Member

    no i rolled out my wheel and also verified by someone in a car beside me not 42mph but kph about 26mph
     

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  2. jaguar

    jaguar Well-Known Member

    sorry I missed seeing that. yeah around 25mph is the normal un-modified max for these engines.
    For more speed you can shorten the pipe header by also shortening the diffuser cone by the same amount.
     
  3. wagel

    wagel New Member

    I tried to calculate based on info given in 2 stroke tuners handbook.

    I would be pretty happy with 45mph but unfortunately I was also talking about km/h. So do you still think its pipe whats limiting or something else? Based on my gearing it should be doing around 6500rpm at the moment. 45mph would be already 9700 :D.
    Also. Whats your thoughts about my transfer situation. Would it be better to have one transfer with normal duration and other one way too much or both equally way too much.
     
  4. zippinaround

    zippinaround Active Member

    Honestly I like mine the way it is nice torque and average top speed , but with a stock exhaust it barely goes anywhere with 0 torque but may experiment you saying if I shorten the header by 1" to shorten diffuser by 1" too?
     
  5. jaguar

    jaguar Well-Known Member

    yes shorten them both by the same distance. Doing so for the diffuser may require a new diffuser with steep cone angle.
    Put all the data in my expansion chamber calculator to see how much you need to shorten to get up to the RPM you want. (don't target more than 9000 and don't do anything before balancing the crank)

    25mph is the top speed for a standard engine and sprockets on a 26" bike.

    my bike was modified to the max and its top speed was around 45mph.

    the pipes top speed and the engines porting top speed have to match.
     
  6. wagel

    wagel New Member

    So. With my pipe the distance from piston to expansion chamber is approx 435mm so I'll try to take out 35-40mm and see how much difference that makes. I tried putting all the data in your calculator with header, diffuser, belly and baffle dimensions from your design but I get some odd numbers. I set target rmp 7500. I get that E6 is .39 and F19 1.43 and if I try to set the header length so that E6 = F19 then header length is 115mm. Am I doing something wrong and what could it be?
     
  7. jaguar

    jaguar Well-Known Member

    making those two numbers equal is to one of two extremes and is only an option of design, not necessary.
    most important is that all the distances add up so that the baffle is the right distance from the piston so the pipe powerband is in the RPM range you want.
     
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