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Thread: Effects of changing sprockets

  1. #21
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    Can you use the dyno chart from twobros website? I know this is all bench racing and all of the results are based on "ideal" conditions I'm just curious as to what the calculations would say is all.

    http://www.twobros.com/Cust_Service/..._FULL_dyno.pdf

    Just realized that doesn't show torque.... let me find a better chart.
    Last edited by Millhouse; 12-21-2011 at 04:42 PM.

  2. #22

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    Since power and torque are directly related through RPMs, I could theoretically get the torque info from a power chart, but the precision of the torque at lower RPMs would be pretty crappy. A high resolution SAE-corrected torque chart with a thin torque line would give me what I need (but not a photo of one, because the chart could be rotated slightly and warped by the camera lens, making it difficult to get accurate measurements). An original dyno run file is even better, because I can load it into DynoJet's viewer and export raw data in 100 RPM increments, rather than taking measurements from a picture.

  3. #23
    Senior Member linkgt's Avatar
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    Quote Originally Posted by UselessPickles View Post
    Since power and torque are directly related through RPMs, I could theoretically get the torque info from a power chart, but the precision of the torque at lower RPMs would be pretty crappy. A high resolution SAE-corrected torque chart with a thin torque line would give me what I need (but not a photo of one, because the chart could be rotated slightly and warped by the camera lens, making it difficult to get accurate measurements). An original dyno run file is even better, because I can load it into DynoJet's viewer and export raw data in 100 RPM increments, rather than taking measurements from a picture.

    If someone can give pickles the info that would be great. I'm curious to see top speed with +1 and exhaust mod+Power commander. I know that when I went +1 front, top speed was reduced for reasons people have mentioned here (Hp needed to overcome drag, etc)

  4. #24

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    Quote Originally Posted by linkgt View Post
    I'm curious to see top speed with +1 and exhaust mod+Power commander.
    Probably not much higher than stock exhaust with +1 up front. Power of drag increases based on the cube of speed. The TwoBros dyno chart shows a 7.7% gain in peak HP. Best case scenario (if the shape of the HP curve near the peak happens to have shifted up in RPMs a certain amount), that could result in a 2.5% gain in top speed (cube root of 1.077 = 1.025), which would be an extra 3mph. Best case scenario is unlikely, so I predict a 1.5-2mph gain.

    Quote Originally Posted by linkgt View Post
    I know that when I went +1 front, top speed was reduced for reasons people have mentioned here (Hp needed to overcome drag, etc)
    Top speed should increase (but barely; look at my comparisons). You probably saw a decrease in top speed because you were looking at your speedometer, which was about 6% optimistic at stock gearing, but nearly correct with +1 up front, which would give the appearance of about a 4mph loss in top speed. If you are comparing actual GPS speed before/after, then it was probably just a difference in wind or slope of the road that caused the decrease.

  5. #25
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    What'd you do the simulation with?

  6. #26

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    Quote Originally Posted by MiltonDorkenhoff View Post
    What'd you do the simulation with?
    Custom software that I'm writing. It has no user interface yet, so I can only feed data in and get data out right now. I've been using OpenOffice Calc (like MS Excel) to make charts of the data.

  7. #27
    Senior Member linkgt's Avatar
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    Quote Originally Posted by UselessPickles View Post
    Probably not much higher than stock exhaust with +1 up front. Power of drag increases based on the cube of speed. The TwoBros dyno chart shows a 7.7% gain in peak HP. Best case scenario (if the shape of the HP curve near the peak happens to have shifted up in RPMs a certain amount), that could result in a 2.5% gain in top speed (cube root of 1.077 = 1.025), which would be an extra 3mph. Best case scenario is unlikely, so I predict a 1.5-2mph gain.



    Top speed should increase (but barely; look at my comparisons). You probably saw a decrease in top speed because you were looking at your speedometer, which was about 6% optimistic at stock gearing, but nearly correct with +1 up front, which would give the appearance of about a 4mph loss in top speed. If you are comparing actual GPS speed before/after, then it was probably just a difference in wind or slope of the road that caused the decrease.
    You could be right. Last time I tried to test top speed was late October and that day was a lot more windy than usual and also felt more drag as well. My buddy however seemed unaffected and got more ahead of me than he usually would, but now I'm guessing it's because of the hurt in acceleration of the +1 up front(causing the bike to take longer to get to top speed) instead of top speed actually decreasing.

  8. #28

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    I added -1/+1 sprockets to the performance comparison: http://www.600cc.org/forum/f89/effec...86/#post314731

  9. #29

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    First of all, THANK YOU! pickles for doing these calculations...extremely informative (and I enjoy this stuff being an aeronautical engineer myslef).

    After reading all of these posts and looking over the info, here is what I summarize.

    Regardless of the gearing combination we are talking fraction of a second differences across the board and in all cases less that 5 MPH differences in speed. For a bike like the FZ6R and the typical experience of teh riders on them...my question is, is it really worth it for these fractional gains/losses??

    My half cent would simply be, put a +1 on the front and be happy that your speedo and odometer are correct...anything beyond that just seems frivilous on this bike.
    Yellow 2009 FZ6R with: TBR Carbon Fiber Full Exhaust, Juice Box Pro, Driven +1 Front Sprocket, Sound Off Vista Cruise Control, Garmin VentureHC GPS, Yamaha Raised Bubble Windscreen, PIAA headlight, Fieldsheer Expander soft bags, Nelson Rigg Tank (or Tail) bag, Scala Rider Q2 headset (a must have!), tank protector, and frame sliders. (and a "Tail of the Dragon" Deals Gap Sticker, a personal favorite mod!!!)

  10. #30
    yellowfz
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    What does -1+0 calculate out at if you do hard takeoff second gear rather than first (giving away secret)? This has always given me good results. Try it even with stock setup it works real well (Warning for experienced riders only).

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