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Originally Posted by 2000SoCalBoxsterS
O.K. I plugged in my variables. Shift ratios same as on your sheet. I have 18" wheels with 265/35 tires on the rear. My owners manual only shows my torque in NM at rpms. They look like this:
Enter Engine Speed, RPM Enter the engine torque, ft-lb
1500 240
2000 258
2500 265
3000 280
3500 285
4000 300
4500 302
5000 302
5500 300
6000 290
6500 265
7000 240
But the Drive Torque Chart output doesn't look right? The Wheel Torque Lb-ft scale is in thousands? Showing me that for example at 25 mph I am at 3500 Ft-Lbs? How am I supposed to read this? Use this info?
The stats on my Boxster from Porsche say I have 250 HP / 225 Ft-Lbs at 6250 rpm
Seems to me based on the graphs in my manual that 4,000 to 5,000 is the peak power band.
What am I missing here? I'm not being critical I just don't understand and I want to learn this stuff.
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It doesn't look like the torque you've got in the columns is correct. You need to have the torque in ft-lb. So it should be 225 at around 6000 rpm and less everywhere else.
Wheel torque in the 2000-3000s in 1st gear is correct. It takes alot of torque to get the car moving quickly.
Then all the plot is telling you is which gear is putting down the most torque for any given vehicle speed (at wide open throttle). If there is a cross-over point from say the 3rd and 4th gear ratios, that's where you'd shift for max acceleration. If they never cross, then you want to shift at redline because you will be making more torque than you would in the higher gear.
Try different torque curves or gear ratios and see what happens to the plot. For example, if a torque curve peaks early and drops off quickly, like a diesel engine would, but your ratios are still tall, you'll see there's alot of crossing of the lines. This would indicate that you want to shift before redline in those gears for the best acceleration.