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torque or hp????

Discussion in 'Lawn Mowing' started by newblade, Aug 9, 2004.

  1. newblade

    newblade LawnSite Member
    Messages: 162

    I am wondering if a 21 hp diesel motor would cut as well as a....say 25hp gas engine due to more torque??? Anyone know this answer? Also what is the difference in 3:73 and 4:11 rear end?
  2. tiedeman

    tiedeman LawnSite Fanatic
    from earth
    Messages: 8,745

    I know that torque is better for like brush cutting.
  3. txlawnking

    txlawnking LawnSite Bronze Member
    Messages: 1,905

    New blade, to answer your questions in order.. 1 torque is the ability to do work, horsepower is the ability to accelerate ( sorta, I am grossly over simplifying this to put it in layman's terms ).... 2 The difference beween 3.73 and 4.11 is the number of turns the drive shaft makes in relation to the axles... In other words 3.73 turns of the drive shaft to 1 turn of the axle shafts. The 4.11 will pull better, but not get as good of fuel economy all other things being equal, generally..
  4. when the growing gets heavy its the torque that counts
  5. dishboy

    dishboy LawnSite Fanatic
    from zone 6
    Messages: 5,883

    If you have torque and horsepower you have something to brag about.
  6. rockhouse

    rockhouse LawnSite Member
    Messages: 42

    Along with that torque you need blade speed.
    A diesel will develope it's torque at a lower rpm. In order to get the blade speed up you have to use a smaller pully on the spindle. To use the smaller pully you need more hp. It's all interconnected. If it wasn't, all cars woud have 25 speed transmissions.
  7. DALMlawn&landscaping

    DALMlawn&landscaping LawnSite Member
    from TX
    Messages: 186

    when i read this it made me instantly bust out the December 2000 issue of petersons 4-wheel and offroad magazine and turn to page 100 (yeah, i sit in my "office" a lot and i have plenty of time to read). it explains torque and horsepower for trucks, but gives up interesting formulas.

    Work = Force x Distance

    Horsepower = lb.ft. per minute/ 33,000
    Horsepower = Torque x rpm/ 5,250

    Torque = Horsepower x 5,250/ rpm

    New Gear Ratio = New Tire Dia./ Old Tire Dia. x old gear ratio

    i'm sure these can be converted to lawnmowers, the gear one i'm not sure what you would use for other then the guys that drive lifted trucks with out making some mods, you'll see what gears you should be running.
  8. Forest

    Forest LawnSite Member
    Messages: 108

    Speaking from experience i can tell you this. Torque is the measure of twisting force, and in this case it would be the crankshaft. Horsepower however is a measure for how long it takes to create torque. Horespower will be smaller or greater depending on the torque. DALM you are correct in you're findings as they come from a reputable source, however, the equation you provided is used to determine the gear ratio needed to retain stock Speedo accuracy when making extreme changes to you're tire sizes on you're truck. For example, switching from a size 275/75/R16 to a 35"12.5"R15. As for desiels, they DO develop torque at a much lower RPM. Anyone with a Desiel truck will notice this looking at the RPM gague. I think most will redline anywhere from 3500 to 4000 RPM as where you're gasoline truck will redline at about 6000-6500 RPM. Secondly, gear ratios are for example, 3.73 gears would mean that you tires will rotate 3.73 times for every 1 rotation of the driveshaft. The HIGHER the gear ratio equals the slower top speed and the worst gas mileage, but it will get there much quicker. That is why drag cars have gear ratios that are astronomical. They need to get to 300 MPH in 3.5 seconds...See what I'm saying??...SO, you decide what's best for you're situation with the info we provide.. GOOD LUCK TO YOU. -Forest
  9. sgt_rjp

    sgt_rjp LawnSite Member
    Messages: 20

    I think that it's actually 3.73:1. That's the gear ratio which states size not rotation. It's inversely related to rotation. So, it takes 3.73 rotations of the drive shaft to rotate the wheels once. The second statement is right. If the first statement was right, 4.11 would give you a higher top speed.
  10. txlawnking

    txlawnking LawnSite Bronze Member
    Messages: 1,905

    Oh forest, BTW top fuel dragsters, the ones you speak of that go 300 mph in a 1/4 mile, Use in the neighborhood of 2.90 gears,Have no transmission other than a reverser to back up after the burnout, and are direct drive after the cluch fully locks up.

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