QUOTE(SirAndy @ Sep 20 2021, 12:12 PM)
QUOTE(Tdskip @ Sep 20 2021, 12:02 PM)
Curious what you all think of this dyno read out?
Shift at 4500 rpm for max acceleration ...
Shift at 4500 rpm for maximum acceleration?
Nope. Shifting near peak torque engine speed will leave a lot of acceleration “on the table”. (Remember you want maximum torque to the rear wheels; not "upstream" of the tranny … each gear multiplies input torque differently based on ratio.) For maximum acceleration you always at least want to rev to peak power (unless for some bizarre reason that’s above redline or there’s a concern about mechanical weakness). Optimum shift points can’t be accurately determined without first knowing gear spacing. For optimum acceleration, the power and torque to the final drive (any point “downstream” of the transmission) at the shift rpm equal the power and torque available to the final drive at that vehicle speed in the
next higher gear (@ WOT of course). Optimum shift points are determined from the available power / torque at the final drive as a function of vehicle speed for each gear. The points where available power & torque in one gear fall below that available in the next gear is the optimum shift point. Often optimum shift points are over the peak power rpm (assuming redline permits). Because gear spacing is not necessarily the same from shift to shift in a given gear set, optimum shift points can vary from one shift to another.
Maybe not the best example, but a random chart from an old college textbook will show the idea. Note that “propeller shaft rpm” is final drive rpm not erpm, and is proportional to vehicle speed. The peak power and torque values differ from gear to gear due to slightly different throughput efficiencies based on gear ratio. The differences in peak torque are additionally related to the different torque multiplications of gears.
So what about the curves not crossing in the chart? One must assume the curves end at engine redline. Therefore torque and power available for acceleration will immediately drop after each shift. This could be avoided with narrower spacing / more gears. The goal being to maximize “area under the curve(s)”.
If vehicle aerodynamic drag (in hp) is plotted on the same chart as final drive power, top speed is predicted by the point where drag crosses available power.
Click to view attachment