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Gearing ~ torque/power

  1. Apr 29, 2007 #1
    anybody know the mechanics of gearing, like on a bicycle, motorcycle, or car?

    what is the relationship between gear ratio and torque/hp? i mean we all know that starting the car in higher gears isnt as easy as first, same goes for a bicycle.....anybody know the details?
  2. jcsd
  3. Apr 29, 2007 #2


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    Gearing multiplies the torque and divides the rate of rotation. If the gearing is a 3 to 1 reduction, then the torque applied at the pedals (bicycle) or from the engine (vehicle) is multiplied by 3, and the rate of rotation is divided by 3 (the driven wheel(s) turns at 1/3rd the rate).

    As mentioned torque is multipled, but power remains the same, because the increase in torque is offset by the decrease in rate of rotation.
  4. Apr 30, 2007 #3

    a fellow classmate told me about a car his friend had (this guy is in his 40s btw, which will make sense as u read further)....he told me his friend had a Pontiac GTO, with a 400ci+ engine (he doesnt remember exactly, but it was huge), and a special transmission that had the following result:

    Engine: V8, more than 400ci, he said mayb 440 or something, but not sure 100%

    Trans type: 4 speed manual

    Speeds @ gears (redline)

    1st - 65mph
    2nd - 95mph
    3rd - 120mph
    4th - he got to 140, but decided not to go further, but said that the pedel had a lot of room left

    so basically we can do crazy stuff like this?!??!?! i mean would that be a custom trans? i mean that isnt stock, but u guys think its custom built or an trans swap from something crazier/aftermarket trans?
  5. Apr 30, 2007 #4


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    That sounds reasonable to me. The shift points for my Roadrunner are 65, 85, & 115. That's shifting at 6,500rpm, which is 1,000 higher than the factory redline.
    I'm not a GM guy, and I'm not going to bother looking anything up, but the 2 main large engines for that car were the 396 tri-power and the 455. He must have had the latter. The gearbox was probably a Muncie M-22 'rock crusher' feeding a Posi-Trac 10-bolt with about 3:1 gears.
    'How Stuff Works' has a section on musclecars that can probably help, as well as checking different GTO owners groups.
  6. Apr 30, 2007 #5
    allright thanks, yea i was just wonderin how reasonable it was u kno

    damn roadrunner...niiiice

    looks like u kno your parts haha, i thought this was custom...

    so your roadrunner is a 3spd manual? or a 3spd auto with a shift kit?
    Last edited: Apr 30, 2007
  7. Apr 30, 2007 #6


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    No. Full race 440 (.030 overbored to 446), A833 4-speed with a long-throw Hurst shifter (4th gear is 0.73:1 overdrive), with a 3.23 geared Dana 60 rear. About 650hp.
    Last edited: May 1, 2007
  8. May 1, 2007 #7
    damn....im gonna need some time to absorb that lol jk

    that is one sick ride...how much it cost? like drivetrain and chassis, not the accessories lol
  9. May 1, 2007 #8


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    I bought her in '75 for $2,500. New, it listed at $8,500. (For comparison, a fully-loaded 'Vette went for $8,000.)
    The engine rebuild was $1,500. As it sits right now, rotting away in my back yard, it'll cost somewhere between $30-50,000 to get it going again.
  10. May 1, 2007 #9
    oh man that sucks..so she dont even run???!?! turn over?!?? lol that sucks....

    yea haha i want a muscle car....i was originally gonna swap something into a 80s camaro, but its unibody so idk if it can take it u kno

    so whats the 0-60 time on yours? 6sec?
  11. May 1, 2007 #10


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    It ran when I parked it, but that was over 20 years ago. The engine will have to be stripped down and cleaned. Most of the expense will be body work and upholstery; there's not much left of either. :grumpy:
    0-60 varied with the surface conditions. On a good dry road, from the time it stopped spinning and started moving, about 3.5 seconds. I usually had to let it spin for at least a second or so first in order to get a decent launch. Quarter mile was 12 seconds @ 115mph, but it got headers after the last time that I tried that. It seriously needs a different cam, though, which should pull it down to 10 or 11 seconds.
    As mentioned in another thread, I've designed an entirely new motor for it (which I'll never be able to afford) that would put out a good 2,000 hp.
    As for a camaro, the first thing that you should always do with overpowering any car like that (including mine) is to weld connecting tubes between the front and rear sub-frames.
  12. May 1, 2007 #11
    if you are running 1000rpm, and you gear it down 10:1 so that it runs 100rpm on other side, the torque will increase 10 times.

    1000rpm with 100oz-in = 100rpm with 1000oz-in with a 100% 10:1 gear down transfer

    Horsepower = Torque x Speed

    Hope this helps
  13. May 1, 2007 #12

    why would u leave it like that? i assume u are married..but still lol...why just let it rot away? i mean u could put it n your garage and run it once a month....

    damn 3.5? thats crazy....

    yea i doubt i can afford such stuff, maybe i'll just get a camaro with a 350 and fine tune it, maybe add the corvette intake, that should add some punch to it....

    so if i get an old muscle car, and assuming the body is in good shape, i could just drop a new drivetrain in with a crazy trans like that and it should run decent? (yea i'm over simplyfying it haha)

    btw u could make some good $$$ on ebay...
  14. May 2, 2007 #13
    Sorry, buy I'm a big Pontiac guy and couldn't help but chime in. There was a 389 tri-power(396 is chevy). A 440 is possible with a Pontiac 428 block bored .060 over. They are actually very strong motors. They don't tend to throw the rods as easily as a 455 because of its shorter stroke and they have the same bore as a 455 so you can actually put just as big of a cam without the low end hesitation. I do think that could be possible without too much modification, considering Pontiac cast iron rods are only rated for 5500 rpm(I've taken mine to 6000+ no rod failure yet).
  15. May 2, 2007 #14


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    Yeah... I caught that 396 error myself, but didn't get around to fixing it. A guy I know has a 389 Goat and a 396 Chevelle. I got the two mixed up. :redface:
  16. May 4, 2007 #15

    btw, what transmission does your roadrunner have? and what engine?
  17. May 4, 2007 #16


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    That's covered in post #6. Sorry I didn't respond to the question about why I left it as is, but it's too complicated to get into just now. :frown:
  18. May 5, 2007 #17
    o ok....no prob...i was just curious....
  19. May 5, 2007 #18
    yea i was just wondering if u had an estimate about the torque output

    0.73:1.....thats crazy, i thought that M-22 was crazy as it is but damn...
  20. May 5, 2007 #19
    actually, wouldn't you want a short throw shifter?
  21. May 5, 2007 #20


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    A short-throw is probably a bit more practical for most people, since it goes from one gear to the next with less movement. I find it preferable to have something that's easy to reach without disrupting my posture. Anyhow, my shifting is faster than my leg and the clutch can react, so I'm not losing time that way. It takes me about 50 milliseconds to change gears, and a lot longer than that to get the pedal down and back up.
    Besides which, the long pistol-grip Hurst is rarer than the short one, so it adds to the value of the car.
    I can't give you a torque figure. Despite it being a big-block, though, I don't think of it as a 'torquey' motor. It doesn't really start making power until over 4,000 rpm. Torque is probably maxed out at about 5,000 while hp is better around 5,500-6,000. If I had to estimate, probably around 500 ft/lbs max.
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