Quote:
Originally Posted by Wositsch
The 125d has maximum power at 4400rpm, then power starts to drop as the revs get higher, thats just the way diesel works. It's the same story with the M50d engine, It has maximum power from 4000 - 4400rpm.
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Correct, but you have to factor in the reduction of the driveline. The Ooomp you'll have at the wheels is basically the engine torque multiplied with the transmission reduction. Accept for the time being, that actual torque on the wheels == acceleration.
For example: engine delivers 200Nm but the transmission line has a reduction of 3 it will bring 600Nms to the ax of the driving wheels. When you shift one gear up, the engine still delivers 200Nm, but the reduction will only be 2,2 (since you need a higher speed range in higher gear, automatically impacting the reduction) bringing only 440Nms to the ax of the wheels. So basically, in this example, engine torque can go down to 146Nm in the first gear before you consider having the shift up to maximize wheel torque. So when you could have 200Nm engine torque of this engine at this speed, you still best conclude to fall down further to 146Nm on engine torque in low gear since the wheel torque is still better!
So don't read a torque/power engine diagram as an indication where you have to shift, always factor in the gear/driveline reductions. But again, no car manufacturer is publishing this, although even LADA already calculated this (really).