Optimal Shift Points

wolf370z

Let's take a look at this stock dyno chart for a 370z.



So you're saying that where you have the most power is where torque starts falling off and horsepower keeps increasing? I realize that torque isn't the only part of the force that's pushing you down the track. That's my real question... what else contributes to the pulling force (i suppose pushing force if you were in a rear engine vehicle).

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Good drivers just drive.

WarmAndSCSI

Let's just ignore wind resistance as a factor for the purposes of this discussion.

Acceleration is directly proportionate to power and weight, so it's definitely the only figure you should be concerning yourself with unless you're qualitatively trying to describe a power curve - then torque is useful. Torque is only a factor when you're talking about engine dynamics, engine internals, and drivetrain strength, etc. It is the instantaneous amount of force your engine is able to slam into the crankshaft - with the crankshaft throw acting as a lever - and subsequently to the wheels. Power is what the road sees.

For the purposes of the dyno graph, you're going to maximize the area under the power curve if you shift right at 7500 rpm (or slightly later) and end up dropping down to 5800-5900 rpm where there is more power available than at 5500 rpm, for example. With our power curve, you sacrifice a little bit of power output at the end of your gear for a lot more power and the beginning of the next gear.

Hopefully that helps.

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wolf370z

So technically you shift according to horsepower since it is the theoretical display of power you're putting to the ground? So that explains why from a 60 roll a 350fwhp honda that makes like 255 ft lbs of torque would embarass a similar weight car with 300fwhp and 300 ft lbs of torque?

However in the 1/4 mile the 300fwhp and 300 ft lbs torque would be faster because it would have more torque to push it off the line? So either way they'd both still be shifting at or near redline (whichever keeps them in their power band which is based off peak horsepower?)

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Good drivers just drive.

WarmAndSCSI

Exactly.

But a 300 lb-ft car may make that torque right at 5252 rpm, so who knows. Generally speaking, low-end torque (i.e. torque between idle and the start of your power band) will get you a better 60' time up to the limit of your tires and suspension, but nothing more unless you're pulling stumps lol

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