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Thread: Half 9 - Diffs

  1. #1
    Hugolech Guest

    Default Half 9 - Diffs

    Just saw this on the kyosho web

    http://www.kyosho.co.jp/web/products...9_ready-e.html



    I wonder if this could fit in the Half 8. No more problems with diffs.

  2. #2
    H8er Guest

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    Actually, it's still the Half 8 . And no, the Nitro has a different tranny. It wouldn't work.

  3. #3
    bluegrooveracer Guest

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    are you sure those diffs won't work ? have you seen a compatibility chart?

  4. #4
    FHM101 Guest

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    Based on gear ratios, I'd say the nitro diffs might be a problem. I have no doubt they might fit in the bulks, but the electric ratio is 11 something to 1, the ST is 12 something to 1, and the nitro is 8 something to 1. By the time you geared down low enough to get the thing moving, if you could do it in the first place, you are going to be getting your motor (especially brushless) awful hot. I'd say it's really going to depend on what's in the center of the nitro, and if it can be made to fit the electric.

    I guess beefier diffs would be nice, but I don't have any problems with the stock buggy or truck diffs in my race cars, so it's really not a big deal for me one way or the other.

  5. #5
    mece Guest

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    Umm, I'm not really following here. does the ST and the buggy have different gear ratios in the diffs?? I doubt that since the st diffs are a straight drop-in to the buggy. the different gear ratio must come from spur/pinion so the diffs would have nothing to do with it. The only part that is really a question is the center diff. I believe that it will require a lot of modding to fit the electric versions. Either way the new diffs look strong and nice, and I really hope they are a straight drop-in (which I believe). If they are, I'm getting some!

  6. #6
    FHM101 Guest

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    Quote Originally Posted by mece
    Umm, I'm not really following here. does the ST and the buggy have different gear ratios in the diffs?? I doubt that since the st diffs are a straight drop-in to the buggy. the different gear ratio must come from spur/pinion so the diffs would have nothing to do with it. The only part that is really a question is the center diff. I believe that it will require a lot of modding to fit the electric versions. Either way the new diffs look strong and nice, and I really hope they are a straight drop-in (which I believe). If they are, I'm getting some!
    Sorry, I was wrong about the differences in gear ratio. All 3 are different, but my numbers were not correct.

    I just got his off the Kyosho America web site.

    Gear ratios: MI 10.8:1, MIST 12.6:1, 09 8.3:1

    Given that the MI and MIST both share the same slipper, center diff, and pinion gears, the difference has to be in the diffs.

    I put ST diffs in my MI last week and without changing anything else, my little buggy has tons more acceleration with the ST diffs than it did with the MI diffs. I'm sure the truck diffs are geared differently to overcome the difference in tire diameter (MI=64mm, MIST=74mm) and weight while the 09 is geared to work with either a different center diff output ratio, or uses the same center ratio and relies on the considerable low end torque difference found between a nitro engine and an electric motor. With a ratio difference of only 1.8:1 between the MI and MIST diffs, my MI accelerates like it's been fired from a slingshot where it used to have a very manageable hole shot with the MI diffs. When you consider that the MI and 09 diffs have a difference of 2.5:1 and the MIST and 09 differ by 4.3:1, the electric cars with 09 diffs are either going to cog like mad, poke off the line, or fry the ESC unless the pinion tooth count is drastically reduced, or the 09 has a higher ratio center diff which can be used in the electrics.

  7. #7
    mece Guest

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    Sorry FHM101, Something is wrong in that argument If all you did was change the diffs then, if they were a different ratio they would also have to be different pitch and therefore you would also have to change the diff pinions. Either way, My MIST and and MI diffs have the same ratio. How do I know this? well I already knew it since they are the same size, but I counted them anyway, and yes. they both have 38 teeth on them and they both connect to 14 tooth diff pinions or whatever you call them.

    I'm not sure about the Nitro MI diffs, but I hope and am pretty sure that they have the same pitch, ratio and size as the other two.
    Last edited by mece; 09-28-2006 at 09:08 PM. Reason: typo

  8. #8
    beep4me Guest

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    I've talked to two people at kyosho on the phone and they both said that the 09 metal diff's are a direct drop in and the same ratio

  9. #9
    Join Date
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    ...theres not really any reason why they shouldnt work...I will check with Kyosho at the Tokyo RC Show in October...

  10. #10
    FHM101 Guest

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    Quote Originally Posted by mece
    Sorry FHM101, Something is wrong in that argument If all you did was change the diffs then, if they were a different ratio they would also have to be different pitch and therefore you would also have to change the diff pinions. Either way, My MIST and and MI diffs have the same ratio. How do I know this? well I already knew it since they are the same size, but I counted them anyway, and yes. they both have 38 teeth on them and they both connect to 14 tooth diff pinions or whatever you call them.

    I'm not sure about the Nitro MI diffs, but I hope and am pretty sure that they have the same pitch, ratio and size as the other two.
    Pitch has nothing to do with the number of teeth unless you are trying to cram a bunch more teeth into the same space. Consider the Losi electric off road truck. All the stock spurs and pinions are 48 pitch gears, but you have a choice of drive pinions that range from 14T up to 25T depending on what kind of motor wind you are running. You also have a choice of several tooth counts for the spur gear. All these different sized spurs and pinions gears are 48 pitch.

    Given the MI and MIST share the same center diff, both have the same center drive ratio. If they have different final drive ratios then the difference has to be in the diffs. I don't doubt the ring and pinion sets on the MI and MIST have the same tooth count, but what about the internal gears? If both cars have the same center ratio and the same ring/pinion tooth count, the difference has to be in the internal gears, otherwise they would have the same final drive ratio and the truck with it's larger tires would be slow as christmas.

    It's the same in 8th truggy/buggy drivelines. When the early examples of truggies were being built, the driveline was simply borrowed from whatever donor buggy was being used. The problem was the larger tires were burning up clutches and the trucks had no holeshot. The simple fix was a larger center diff gear and a lower tooth count on the clutch bell to increase the overall final drive ratio. These huge center diff gears created problems with engine mount location, forcing it further away from the centerline and upsetting the weight balance and shifting the polar moment to the engine side of the centerline. It also forced a taller center diff assembly which altered the CG in a negative way. The second generation truggies like the ST-R and MBX5T solved both of these problems by changing the internal ratio of the front and rear diffs which allowed the use of the smaller buggy ring and pinion sets, center gears and clutch bells. By lowering the center diff assembly and moving the engine back inboard, it made a dramatic change in handling so the newest truggies handle almost exactly like their buggy ancestors. In fact, with the exception of different shock oil weights and mounting locations for the new shocks, most folks running the MBX5T are just duplicating their MBX5 buggy setup on their trucks with great results.

    Please don't get me wrong here, I don't know any more than anyone else outside Kyosho about the differences which give the MI and 09 a different final drive ratio. Since the MI and MIST have different final ratios and share a center diff and ring/pinion tooth count, the only place left for the difference to come from is the internal ratio of the F/R diff. As I said in an earlier post it could well be that the difference between the MI and the 09 final drive ratio is found in the center diff/clutchbell. If that's the case, the F/R diffs for the 09 and the MI could have the same internal and external ratios but the two cars would still have a different final drive ratio.

    I don't think the MI diff problems have been lost on the engineers at Kyosho, and it would have been a very wise move to design a stronger, more solid diff for the 09 which would be a drop in for the MI while making the ratio change in the center since it most likely had to be designed from scratch anyway for nitro power. My speculation was based on the final drive ratio differences between the MI and MIST and where that difference comes from.

    In any case, the 09 will be out soon and I'm sure plenty of MI owners will be giving the 09 diffs a try so we will know soon enough.

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