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Re: Shift points for the highest torque?
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Posted by MarkB on October 05, 2003 at 04:21:06 from (64.79.80.28):
In Reply to: Shift points for the highest torque? posted by Cliff on October 04, 2003 at 23:30:45:
An engine produces maximum "pulling power" at whatever rpm it produces maximum horsepower. They are the one and the same. This is rarely the same rpm that produces maximum torque. Since power is a function of torque times rpm, an engine that produces maximum torque at a low engine rpm will have a relatively flat power band. That is, the horsepower will be almost constant across a wide range on engine rpms. As the rpms increase, the torque decreases so the horsepower remains almost constant. This describes most truck engines. Such engines are relatively insensitive to shift points, since the horsepower doesn't drop significantly when you upshift. Still, you'll probably get best acceleration when you wind the engine up to the redline before shifting. On the other hand, engines that produce maximum torque at a high rpm have a very narrow power band. They produce enormous power, but only when they're really wound up. This describes most high performance automotive engines. They must be kept at high rpms, because they don't produce much power at low speed. Hence you need to redline them before shifting. In the case of your tractor, you're correct that it probably produces maximum horsepower when the PTO rpm is around rated speed (540 or 1000 rpm). It's designed this way. Note that maximum torque will be produced at a much lower rpm. In an aside, it's interesting to note that piston steam engines produce maximum torque at zero rpm. That's why they don't need transmissions.
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