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Old 12-13-2002, 10:46 PM
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Let me see if I understand your question correctly;
  • You want to know if you design an engine to produce unbelievable amounts of torque at low rpm would this be an advantage over engines that need to rev at a higher rpm to develop their equivalent torque?

This question is best answered by examining how gearing affects torque multiplication. A rear axle of lets say 2:1 would multiply the torque available at the rear tires X2.

Now if we had an axle of 4:1 the torque would be multiplied X4, a significant increase. Lets say this engine developed a peak of 100 pd ft of torque at 2000 rpm. The rear tires would see 400 ft pds being exerted through the lever (the tire, it has a diameter!) to the ground, lets say the lever is 1 ft long (Most 15 inch tires approach this) So exactly 400 ft pds are being exerted at the rear tire at peak load at 2000 rpm. Sounds like a real torquey motor hey? Rpm would also go down by 4 since we are trading rpm for torque.

Lets look at the same motor with the 2:1 gearing, we have 100 ft pds going through X2 equals 200 ft pds at the 1 ft lever. This the basic reason why you cannot increase hp by reducing gearing, it's straight multiplication and low gearing is a direct multiplication of the torque function. Of course rpm would go down by only half.

Designing a motor with a low operating rpm and narrow power range will be hard to gear because of the need to keep the engine turning at peak torque over a narrow range. Essentially you need a lot of gear changes to keep the engine working. Look at semi trucks, this is how they extract work from narrow power range diesels.

Work is time X effort / distance covered, Horsepower represents this work in a rotational fashion by using rpm to denote distance covered. Think of it as an endless fishing reel pulling in the big one. The faster you can reel in and the bigger the fish and the more line you can reel in one second the more work/horsepower you are producing. Fish weight (load) is a direct multiplier just like the gearing calculation. The basic math mistake you are making is rpm or distance covered is a divisor into the time/effort numerator, not multiplied.

Whew. <img src="graemlins/sweat.gif" border="0" alt="[sweat]" />

[ December 14, 2002: Message edited by: 4 Jaw Chuck ]</p>
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