Re: Shift points for the highest torque?

Posted by Rod F. on October 05, 2003 at 19:54:44 from (142.177.109.2):

In Reply to: Shift points for the highest torque? posted by Cliff on October 04, 2003 at 23:30:45:

Hi Cliff,

The exact shift points would depend on the torque and power curves for a particular engine. As mentioned below, maximum pulling power is at the engine's maximum power. The torque curve also has considerable effect on acceleration and lugging ability. Another consideration is torque rise, which is the percentage increase in torque from torque at rated speed to torque at maximum. This draws the torque curve. As an example, my Ford 7710 has a Ford 268 turbo engine. The engine is rated at 103 hp gross, at 2100 rpm. That equals 257 lb-ft of torque at rated speed. The maximum torque is about 300 lb-ft at about 1400 rpm. (Just a rough guess, as I don't have the exact specs.) This leaves a torque rise of 17 percent, and a relatively flat torque curve, with a steep power curve, and maximum power at 2100 rpm. There is roughly 80 gross hp at maximum torque. This engine is rather balanced for lugging ability and acceleration. Some engines have much higher torque rise, with steeper torque curves, and flatter power curves. An example would be the Cummins 350 Formula in my truck. Max power is 350 at 1800, while max torque is around 1300 lb-ft at say 1400 rpm. This engine has much higher torque rise, so it lugs better, but it can't accelerate nearly as well. I find the cummins has a much better chance of picking up the gear when the engine is kept as high as possible (out at 22, and in at 17). The big advantage of the flatter torque curve is that the old Ford can pick up anywhere above 1200 rpm, which is below the maximum torque, but still very close. It would take a miracle for the cummins to do that. One of the big advantages of the electronic controls and wastegate turbos on new engines is that they can compensate for a lot of the problems I mentioned in both of the above examples. The Ford can be made to lug better, while still accelerating, and the cummins can accelerate better while still maintaining it's ability to lug. Torque and power curves are now less dependant on cam profile, to some extent. Well, since I now confused some and bored the rest to death, I'll sign off.

Rod

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• Re: Re: Shift points for the highest torque? Cliff 20:32:09 10/05/03 (0)

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