Re: Could someone educate me?

Posted by KEB on March 23, 2006 at 19:46:27 from (207.94.26.1):

In Reply to: Could someone educate me? posted by chadd on March 23, 2006 at 11:58:50:

Alright guys, here's the deal...

For the sake of this discussion we'll ignore losses in gearing & bearings.

Horsepower is horsepower, period. Torque is a measure of the rotational force available at the measurement point. How much power (the rate of doing work) is available is a function of the torque and the rotational speed (i.e., HP = torque x RPM x constant).

If you were to take a ricer engine making 100 HP at 6000 RPM, and put a reduction gear on the end of it to reduce the speed to 1600 RPM, it would make exactly the same torque as a 100 HP tractor engine turning at 1600 RPM. If you were to then drop this ricer assembly into a tractor frame so that it had equivalent weight (& therefore traction), it could in fact pull the same load as the same tractor with a 100 HP tractor engine.

How long it would last under those conditions is a whole 'nuther issue, which we won't go into here.

Remember, when you change speeds via gearing (and ignoring losses) the torque is multiplied by the inverse of the speed ratio. For example, a 100 HP engine at 6000 RPM is producing 87.5 ft-lbs of torque. If we gear this down to 1600 RPM, we now have 328 ft-lbs of torque and our original 100 HP available at the output shaft. Works the same way in reverse, if we were to take our 100 HP tractor engine, and run our reduction gear in reverse to produce a shaft speed of 6,000 RPM, we would now have 87.5 ft-lbs of torque and 100 HP available at the output shaft.

The big difference between tractor and car engines (besides the fact that a tractor engine will last many time longer than a car engine) is that tractor engines are made to produce maximum power at a constant or very narrow RPM range, whereas car engines are made to produce power over a wide RPM range. Additionally, there is an advantage to having a heavy tractor engine, and there is an advantage to having a light car engine. I'm sure there are other design considerations as well, but these two come to mind quickly.

The difference in pulling power between a tractor and a rice burner is a function of gearing, weight, and traction. If you took a rice burner, geared it down to where its top speed was 4 miles per hour, and could get unlimited traction with those silly little tires, it would in fact pull what a tractor with equivalent horsepower can pull at 4 mph, also assuming unlimited traction.

The reality of the situation is that a tractor is designed for pulling, and a car is designed for speed, and there really isn't an apples to apples comparison between them.

Now if we could just convince the younger generation to get rid of the ricers & go back to good old american iron, we might get somewhere.

Keith

Replies:

• Re: Could someone educate me? KEB 20:09:45 03/23/06 (1)
  • Re: Could someone educate me? RN 20:54:53 03/23/06 (0)

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