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VTR 250 straight through exhaust

Discussion in 'Modifications and Projects' at netrider.net.au started by chunkylover54, Mar 23, 2008.

  1. anyone ever done a muffler without baffles on vtr 250?

    we were thinking make it longer and fatter to reduce noise, with 1 1/2" pipe inside. also longer pipe will deepen the note.

    has this been done?

    cheers


     
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  2. That's what a staintune is, straight through but with sound absorbing stainless steel packing.

    Keep it quiet...

    Cheers

    Trevor G
     
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  3. And Megacycle, etc, yeah.

    They're not hard to make - I designed and fabbed several different 'glasspack' muffler configurations for a CBR600F4i-powered open wheeler.

    Straight-through 'glasspack' mufflers sound pretty good on the little V-twin; a relatively 'meaty' sound given the displacement. Just add 'nuts and bolts bouncing around in a cement mixer' Ducati clutch-rattle and you're set. :)
     
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  4. anyone know what size perf pipe staintune has for vtr 250?

    we are calculating from the size of the header pipes to use an 1 3/4 perf with a 5" x 600mm body. plus a few other special little tricks.

    Someone told me staintune is baffled for back pressure. BOLOGNE!
     
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  5. Not sure! I sold my VTR (w/ megacycle muffler) to a friend. It'd be logical to keep the pipe the same diameter as the "1" part of the 2-into-1 Y joint.


    The "engines need backpressure!" thing is a bit inaccurate, terminologywise.

    Engines need proper 'scavenging' effects. Tuned-length scavenging (which only happens at certain engine speeds, and hurts power on the others. Harmonic wavelengths!), and kinetic scavenging (by keeping gas velocities high).

    'course, if you use small diameter pipes in order to increase gas velocities, to improve scavenging at low RPM... top-end performance is hampered by the flow losses.

    Big fat pipes will flow huge amounts of gas at the top end with little restriction, but the bottom end of the torque curve will inevitably suffer because there's no gas velocity at low rpm.



    Staintune does have removable baffles to help reduce noise when on the street. I don't know if the muffler has permanent baffles in addition to this. Would suspect it to be unlikely, but without one in front of me I couldn't say.

    I'm preeeeeetty sure my megacycle was completely straight-through and unrestricted. My uncalibrated butt dyno thought the lower end suffered a little bit perhaps, but the butt dyno is easy to confuse, and it sounded and looked great so who cares. ;)
     
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  6. my 2 into 1 is 2"...

    The "engines need backpressure!" thing is a bit inaccurate, terminologywise.

    Engines need proper 'scavenging' effects. Tuned-length scavenging (which only happens at certain engine speeds, and hurts power on the others. Harmonic wavelengths!), and kinetic scavenging (by keeping gas velocities high).

    'course, if you use small diameter pipes in order to increase gas velocities, to improve scavenging at low RPM... top-end performance is hampered by the flow losses.
    [/quote] low RPM=nothing to scavenge IMO


    Big fat pipes will flow huge amounts of gas at the top end with little restriction, but the bottom end of the torque curve will inevitably suffer because there's no gas velocity at low rpm.



    Staintune does have removable baffles to help reduce noise when on the street. I don't know if the muffler has permanent baffles in addition to this. Would suspect it to be unlikely, but without one in front of me I couldn't say.

    I'm preeeeeetty sure my megacycle was completely straight-through and unrestricted. My uncalibrated butt dyno thought the lower end suffered a little bit perhaps, but the butt dyno is easy to confuse, and it sounded and looked great so who cares. ;)[/quote]
     
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  7. Sounds like you're talking 2-strokes there Spots. 4-strokes have exhaust valves which pretty much deal with any sort of exhaust back pressure during the balance of the engine cycle.
    That being if the exhaust pipe & 'can fitted is not restrictive at all, whole different ball game if the exhaust gases have to do cartwheels before they enter the atomosphere.

    Tuning the engine should only really have to be done if the inlet 'system' is altered, ie: removal if inlet tract restrictors, diff cams, diff valve sizes, open up the airbox, diff carb jets, FI mapping etc.
     
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  8. *waggles a hand* It's correct that 2-strokes need far greater attention paid to scavenging effects, but 4-strokes are still affected. And why settle for a-bit-more-than-atmospheric-pressure backpressure when good scavenging design can get you below atmospheric pressure?

    A badly designed exhaust will see the exhaust valves shutting with hot combusted gasses still inside the cylinder, reducing the amount of fresh charge the cylinder's willing to accept when the inlet valve opens.

    (the same harmonic and kinetic effects play a part on the intake system design, too)
     
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  9. well, just to keep you all in the loop...

    We've gone for 1 3/4 inch from the collector to 1 3/4" straight through perf, 4" body packed with stainless steel wool.

    The question now is how long do we make it. Dude building it says 600mm to a)extend the length of the pipe to increase gas velocity, b)to make it a little deeper sounding and to try to get rid of any buzz that might occur...

    opinions welcome...
     
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  10. for anyone who cared

    so here's the finished product, comments and constructive criticism welcome :)
    aV1HkICS.


    we cut off the original collector too, as it was crap, and made a proper collector, with the 1 and 3/4 pipe coming straight out of it.

    Packed with steel wool, I'm glad we did cos it is pretty loud...
     
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  11. WOWsers! very nice.... good work!

    Care to youtube?

    Care to make one for me? :) $$?
     
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  12. Re: for anyone who cared

    Looks OK.

    Install an outlet baffle about 15cm long and about 22 mm ID to knock it back a bit.

    Cheers

    Trevor G
     
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