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  4. DT 125 R '88... New project

DT 125 R '88... New project

Scheduled Pinned Locked Moved DTR
89 Posts 11 Posters 26.0k Views 1 Watching
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  • J jgr72

    Hmm... that's true also... So if I want to use boost bottle, I need to enlarge it about 35% to be in the same as previously 125cc!

    CalumC Offline
    CalumC Offline
    Calum
    wrote on last edited by
    #80

    @jgr72 I think it's a little more complicated than that. As said it's all to do with Harmonics and the resonance frequency of the engine at a particular motion in the engines cycle.

    I don't know the specifics in intimate details but the idea is this.

    At some point in the engines RPM cycle, there is a dip in the air pressure and consequently the engine will perform less than optimally. They characterised this phenomena with a certain frequency. They then created a body with a natural frequency that matches the signature of this phenomena. When the engine hits this frequency, and is down on oxygen, the bottle resonates, forcing reserved air into the inlet tract. This makes up for the loss charge during this period and as a result performance is restored.

    Now to my mind, there are so many factors that have to be considered that it's either pure genius or pure myth...it's hard to say whether the performance with or without is noticeable, it's probably so slight but the Japs just over engineer it all.

    Always Originate, Never Pirate!

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    • CalumC Calum

      @jgr72 So I'm running a Dellorto VHSA 32mm on stock inlet manifold with no issues.

      Irongamer727I Offline
      Irongamer727I Offline
      Irongamer727
      wrote on last edited by
      #81

      @calum was it really worth changing to a 32mm carb? I mean it's only a 4 mm difference from stock? Thought those 28mm mikuni carbs were well up for the job. I'm still running the 28mm with the 170 kit.

      CalumC 1 Reply Last reply
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      • Irongamer727I Irongamer727

        @calum was it really worth changing to a 32mm carb? I mean it's only a 4 mm difference from stock? Thought those 28mm mikuni carbs were well up for the job. I'm still running the 28mm with the 170 kit.

        CalumC Offline
        CalumC Offline
        Calum
        wrote on last edited by
        #82

        @irongamer727 It's not just the fueling, it's the amount of air you can get in as well. My brother ran a 38mm Keihin carb on his, although to be fair that was probablyt way too big. 32-34 is about right I'd say. The Aprilia RS125 ran 34 as standard and they were making 26-33bhp.

        Always Originate, Never Pirate!

        declanD 1 Reply Last reply
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        • CalumC Calum

          @irongamer727 It's not just the fueling, it's the amount of air you can get in as well. My brother ran a 38mm Keihin carb on his, although to be fair that was probablyt way too big. 32-34 is about right I'd say. The Aprilia RS125 ran 34 as standard and they were making 26-33bhp.

          declanD Offline
          declanD Offline
          declan
          wrote on last edited by
          #83

          @calum are there any of the aprilia engines that don’t have right hand drive?

          CalumC 1 Reply Last reply
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          • declanD declan

            @calum are there any of the aprilia engines that don’t have right hand drive?

            CalumC Offline
            CalumC Offline
            Calum
            wrote on last edited by
            #84

            @declan Aprilia didn't make their engines. Just swap the swingarm when you do the engine. Simples.

            Always Originate, Never Pirate!

            declanD 1 Reply Last reply
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            • CalumC Calum

              @declan Aprilia didn't make their engines. Just swap the swingarm when you do the engine. Simples.

              declanD Offline
              declanD Offline
              declan
              wrote on last edited by
              #85

              @calum well uno out of the Rotax engines but what if it’s an sm

              CalumC 1 Reply Last reply
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              • declanD declan

                @calum well uno out of the Rotax engines but what if it’s an sm

                CalumC Offline
                CalumC Offline
                Calum
                wrote on last edited by
                #86

                @declan Just get an mx mate, much better bikes.

                Always Originate, Never Pirate!

                declanD 1 Reply Last reply
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                • CalumC Calum

                  @declan Just get an mx mate, much better bikes.

                  declanD Offline
                  declanD Offline
                  declan
                  wrote on last edited by
                  #87

                  @calum ahh okay

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                  • J Offline
                    J Offline
                    jgr72
                    wrote on last edited by
                    #88

                    Bike is getting ready for next summer:

                    alt text

                    That exhaust chamber :smiling_face_with_heart-eyes:

                    alt text

                    Gianelli silencer:

                    alt text

                    But need to twist something:

                    alt text
                    alt text

                    I guess it's easier to warm and twist + cat a little bit of that exhaust chamber tail pipe... Gianelli's aluminium would melt away too easily...

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                    • CalumC Offline
                      CalumC Offline
                      Calum
                      wrote on last edited by
                      #89

                      Looking lovely, I'd be reluctant to bend the pipe, just make up a larger bracket and move it closer.

                      Always Originate, Never Pirate!

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