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Thread: 2-1 on Sportster Iron

  1. #1
    jerryaurum Guest

    Question 2-1 on Sportster Iron

    Hi from Jakarta, Indonesia.

    I might be one of the firsts who tried Supertrapp 2-1 on Sportster in Indonesia, so there aren't many people to discuss with here.

    My Sportster only runs 800km at the moment, and I've told that it's not recommended to go to dyno and get it properly tuned before 1600km (after 1st service). So I have to wait.

    I installed Supertrapp 2-1 with 16 discs and closed cap 2 weeks ago, it was nice. I think the engine was a bit hot though (whitish spark plug color). I then tried 6 discs with open end cap, the torque wasn't as nice, and it was popping during deceleration. I tried 4 discs with open end cap, the popping was still there, but not too much anymore. The engine felt a bit hotter, and the spark plug was even whiter. I was confused.

    I now try 2 discs with open end cap, and the engine is even hotter (I thought it should be cooler, richer). Haven't checked the spark plug again.

    I know that I have to get it dynoed once I can, to get the engine properly tuned. I've also told that I should get the sound right first, before the dyno. That's why I chose the open end cap.

    1.Is the performance with open end cap actually better than close cap, as I assume?
    2.What to do at the moment? How many discs to put?

    Thanks so much. Regards from hot tropical country!

  2. #2
    Join Date
    Jul 2007
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    Performance differences between an "open" and "closed" end-cap on a streetable machine should be negligible. The Open end cap is benificial if sound volume or a reduction of discs is desired.

    You should have been in the ballpark with 15-16 discs and the closed end-cap and near the same rate of exhaust flow with the open end-cap and 5-6 discs.

    Are you riding the machine enough in between (disc/cap) changes to allow the ECM to make it's system adjustments (A/F ratio) to the "new" flow rate?

  3. #3
    jerryaurum Guest

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    Thanks for the input . I was riding around 30-100km after each change, so I think that should be enough, right?

    Also, I noticed, with 2 discs + open end cap, it feels the sound is louder than 6 discs + open end cap. Is that possible? Less discs = less sound, isn't? I want louder sound with good performance.

    Thanks again!

  4. #4
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    It's possible, with less discs (being more restrictive) you are forcing more exhaust out through the end cap (less resistance and less dispersion through the discs) giving resulting in more sound.

  5. #5
    jerryaurum Guest

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    Thanks bschultz. One more question. As open end cap equals 10-12 discs, why do I feel that 6 discs + open cap has less power thank 16 discs + close cap? Is that normal, or should it be the other way around? Is it only because I haven't get it tuned/dyno properly?

  6. #6
    Join Date
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    You may very well be correct in that your machine does perform better with the closed end cap combination. We can only talk in general terms and norms. There are many variables and potential combinations which work together.
    If you pulled two bikes, same models comparably equipped, off the assembly line and did dyno pulls on both, there would be disparities.
    The disc assembly is a tool that can allow you to find the best performance with your bikes components.

  7. #7
    jerryaurum Guest

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    Tx a lot for the info!

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