i'm gonna try to throw a wrench in here and say the guy and datsuns.com doesn't know what the hell he is talking about.

maximum acceleration happens when average power (not torque) is maximized over the course of the acceleration. if you are shifting based on the torque curve rather than the power curve then you are leaving LOTS of power and ET on the table.

and yes you do have to consider power pre and post shift in each gear (that's why it's average power that's important). but if you have a properly tuned engine, your optimal shift points will always be at redline.

 

I spent a few hours reading a bunch of different articles on the subject and they all came to the same conclusion. Also, that program I provided the link to does not require you to input horsepower data, but rather torque data. It makes sense to me.

I do agree that with a lot of cars, the optimal shift point is going to be at or very near redline. But with some cars that make peak torque much lower, I don't think that will be the case. I am trying to find an example to use. In any event, I find it pretty interesting.

 

how about a car with a nitrous mod? here's a link of a dyno (click 06 mustang and zex or nos for power adder).

http://www.speedshoppro.com/GearCalc...ScoreCard.html

that mod's torque peak is 4000 rpm, 600rpm lower than NA version. I'd be very curious if anyone running nitrous on 05+ stangs would recommend a shift point 600 rpm less than NA.

torque is instanteous "rotational" force. power is force through distance over time. power and torque are intimately (and mathematically) related, but at the end of the day it's about power if you are talking about acceleration.

assuming a completely flat torque curve, which would you rather have? 450 ft-lb torque with a redline of 5000rpm? Or 350 ft-lb at redline of 8,000 rpm? which one would go faster? the lower torque car (assuming equal weights, etc) all day long.

 

http://www.allpar.com/eek/hp-vs-torque.html

Good article

 

crazy *** artical right there but makes sense

 

Hmmm....I wonder which shifting method the author used -> granny, speed, or power?

 

yes. this guy definitely has it right. shift to maximize torque applied through drivetrain WhICH is equivalent to maximizing power because HP= Torque* rpm/5252.

 

Hi paco_pony,

I'll take 8,000RPM and the much higher axle gear ratio to multiply the lower torque and be waiting for you at the finish line. Because of torque multiplication the motor with less torque and 8,000RPM limit will be able to use an axle ratio 40% higher and as a consequence lay down more power. Do the math if you don't believe me.


HTH

 

Umm.. the guy hasnt made apost in over a month...

Whats up with all these older threads being dragged back to life lately?

 

Good point. I'll elaborate on this a bit.

Choosing your shift point based upon the torque/power curve certainly seems intuitive and sensible. Taking the time to work the science and math is usually beneficial, and certainly smart for racing.

However, there are some other things to consider. As Ski mentioned, the manner in which you shift also effects the way you accelerate.

Lets say for the sake of argument that you, or perhaps a computer could automatically adjust the rpm of the engine to match your transmission when you shift. In this case where there is little or no slippage, using a computed shift point is clearly better. The machine is acting in an ideal manner.

But what if you power shift? Maintain maximum engine speed and WOT during the shift? In this case, the momentum of the flywheel and its higher speed compared to the clutch creates dynamic friction. Until the engine and transmission reach the same speed, the dynamic friction effectively creates an additional "gear" through torque multiplication.