Shift Points for Maximum Acceleration

[z281974]

Excellent data and explanation blue2000s. Its torque at the wheels and only torque at the wheels that accelerates the car. Everything else is just an "old wives tale" repeated over and over, but still not true. If you're getting more torque at the wheels in first gear even beyond engine torque peak, then you stay in first gear until wheel torque is higher in the next gear or you hit redline. Every car (and motorcylce) is different and must be analyzed with this type of chart to determine shift points. I'm a state licensed professional engineer, so I speak with some knowledge of physics and mechanical engineering principles.

Tom

[Rondog]

I've GOT to invite you guys my next cocktail party!!!!

Cheers!!!!

[blue2000s]

Originally Posted by Rondog

I've GOT to invite you guys my next cocktail party!!!!

Cheers!!!!

Every time I've seen engineers at a cocktail party, they can only entertain each other.

[denverpete]

Originally Posted by blue2000s

Every time I've seen engineers at a cocktail party, they can only entertain each other.

Hmmm, this coming from an Engineer? If by entertaining each other they have discussions like this thread - then YEAH, small surprise there.

Personally, I've got better things to do at a party than bore people with detailed discussions of engineering and physics. For example, you can always bore them with Politics and Religion....

[blue2000s]

Originally Posted by denverpete

Hmmm, this coming from an Engineer? If by entertaining each other they have discussions like this thread - then YEAH, small surprise there.

Personally, I've got better things to do at a party than bore people with detailed discussions of engineering and physics. For example, you can always bore them with Politics and Religion....

We talk about what interests us which ends out boring everyone else including spouses and friends. When I see my lady's eyes gloss over (she's an actress with no interest in engineering whatsoever so it happens pretty quickly) I know it's time let her break away.

Usually I can find a couple of other car guys who like to talk about Porsches and Rx-7s.

Now we're totally off topic.

[Brad Roberts]

Great thread!!

I shift when it is safe. LOL

Try this: turn 8 at Willow Springs entering the corner at 120mph almost at redline in 4th gear. In theory I should up shift. No thanks. If I lift for the shift I'm spinning the car at 125mph

I have used this for years in drag racing: shift 500-800 RPM over peak torque to do exactly what has been described above. Hit the sweet spot that keeps the car accelerating.


B

[MNBoxster]

Hi,

I think there's still quite a bit of confusion here.


Horsepower = Torque * RPM / 5252



The number 5252 works only with Torque in ft-lbs. Torque measured in other units such as Newton Meters or kg-m require a different number. Visualize a one pound weight, one foot from the fulcrum on a weightless bar. Rotate that weight for one full revolution against a one pound resistance, it moved a total of 6.2832 feet (π * a two foot circle), and, incidentally, it has done 6.2832 foot pounds of work.

Now, 33,000 foot-pounds of Work/min. equals one horsepower. Divide the 6.2832 foot pounds of Work/revolution of that weight into 33,000 foot pounds, = one foot-pound of Torque at 5252 rpm or 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute), and so on.

• Maximum acceleration at any speed occurs at the HP peak.
  Maximum acceleration in any gear occurs at the torque peak
  Horsepower = Torque * RPM / 5252
  Torque = Horsepower * 5252 / RPM
  Torque = Horsepower at 5252 RPM

What is not being discussed is the Torque Curve, that is, how long an engine can operate at peak Torque throughout the RPM range.

Example: 2 Cars, each producing 300 ft. lbs. of Torque. Car #1 reaches Peak Torque at 4200 RPM and it's curve falls off at 4700 RPM. Car #2 Reaches Peak Torque at 4200 RPM but it's curve doesn't fall off until 5300 RPM. Car #2 will be faster.

Without a look at the curve, the raw numbers can be very deceiving...

Happy Motoring!... Jim'99

[blue2000s]

Originally Posted by z281974

Excellent data and explanation blue2000s. Its torque at the wheels and only torque at the wheels that accelerates the car. Everything else is just an "old wives tale" repeated over and over, but still not true. If you're getting more torque at the wheels in first gear even beyond engine torque peak, then you stay in first gear until wheel torque is higher in the next gear or you hit redline. Every car (and motorcylce) is different and must be analyzed with this type of chart to determine shift points. I'm a state licensed professional engineer, so I speak with some knowledge of physics and mechanical engineering principles.

Tom

Thanks Tom, I'm a mechanical engineer as well. Just trying to spread a little knowledge.