Torque curve gearing comparison

Have you ever seen a torque curve? They are fascinating (OK, well maybe not to everyone). But it is pretty powerful to be able to see how power is distributed over the RPM that an engine puts out. As RPM increases, the torque rises up to the sweet spot, then drops off at some point beyond that. Anytime you move outside of the sweet spot fuel consumption jumps. And at some point torque itself drops off.

This calculator is available on zfactorconnect.com. It’s a powerful comparison of different gearing scenarios. If you keep all three scenarios on the left equal, but change only the ratio, you can see the differences between 2014 truck ratios and 2017+ ratios. When you are trying to express to your customer that their previous truck gearing is not a recommendation for today's downsped engines, this printout will give the customer something to contemplate.

Every engine has a different torque curve. Family 1 engines on the Cummins side are designed to influence driving habits by taking power away once the engine rpm exceeds the sweet spot. By lowering torque the driver is forced to downshift and the RPM once again aligns near or inside the sweet spot. That’s why when you talk about fuel economy Cummins wants to put you into a Family 1 engine, today referred to as Efficiency engines.

Sweet spot is a term tied to fuel economy. Operating bands are gearing targets based actual application, not everyone has fuel economy as their primary objective. Some applications warrant a Balance between economy and performance, and some applications gear strictly for performance (vocational heavy as an example).

And now…

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