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What really torques me...


Have you ever looked at a torque curve? Its quite amazing what it tells us about the engine performance. If you have never seen one, here are the basics of the design. Torque is listed in increments up the RH side of the graph. RPM is listed in increments across the bottom of the graph. The torque curve, the orange graphed line, defines the intersect of torque at given RPM points.

  • The engine associated with this example curve idles at 600 RPM, as illustrated by the initial point at the far LH side of the curve.

  • This engine creates a maximum of 1650 ft. lbs. of torque, as illustrated by the highest portion of the curve.

  • Peak torque is achieved at 950 RPM, which is the point at where maximum torque, in this case 1650 ft. lbs., is achieved.

  • The green area is the sweet spot, which is where the manufacturer wants this engine to do most of its work, where it is efficient.

  • Maximum torque can be used all the way to 1430 RPM (approximately). At this point the torque begins to drop off. This is realized as a loss of pulling power.

This is all good, but most people speak about horsepower, how do we know what that value is? The equation is simple: HP = Torque X RPM / 5252 (this value is a constant)


HP = 1650 X 1430 (max RPM) / 5252, or HP = 450


So, with another engine, where the torque was also 1650 ft. lbs., higher horsepower is achieved by extending peak torque to a higher RPM. If 1650 was extended to an RPM of 1550, then the math would tell us that engine is around 485 HP. This curve would permit the driver to operate the engine at a higher RPM, because they would not be losing torque. Keep in mind, the operation would be further from the recommended operating range, meaning some efficiency is lost. In this case, that loss is fuel economy. The higher RPM that the engine operates at, beyond the Sweet Spot, the more fuel that is burned to maintain torque. Which may not be objectionable, depending upon what the expectation is.

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