Shift Points for Maximum Acceleration

[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 MNBoxster

[list]Maximum acceleration at any speed occurs at the HP peak.
Maximum acceleration in any gear occurs at the torque peak

Wow. Don't confuse torque with power, they're directly related but totally different and can't be used like this.

If you go back to the fundamentals, force=mass*acceleration, torque is a twisting force. It can be directly calculated to force by the wheel/tire radius, therefore it is the property that defines acceleration.

[MNBoxster]

Originally Posted by blue2000s

Wow. Don't confuse torque with power, they're directly related but totally different and can't be used like this.

If you go back to the fundamentals, force=mass*acceleration, torque is a twisting force. It can be directly calculated to force by the wheel/tire radius, therefore it is the property that defines acceleration.

Hi,

Yes, you are correct in pure physics, but in Autodom, and especially in the context of this thread, the term acceleration is, strictly speaking, misused and does imply a time component and work being done. You can generate 300 ft.-lbs. of Torque at 4000 RPM the instant the Clutch is released (from a dead stop), but the Car isn't yet doing any work.

There is really only Torque. Torque is the only thing that a driver feels, and Horsepower is just sort of an esoteric measurement in that context but adding in a time component.

300 foot-pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would double at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where Horsepower and Torque always come out the same.

In contrast to a Torque curve, Horsepower rises rapidly with RPM, especially when Torque values are also climbing. Horsepower will continue to climb, however, until well past the Torque peak, and will continue to rise as engine speed climbs, until the Torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver feels.

It is better to make torque at high rpm than at low rpm, because you can take advantage of gearing.

An extreme example of this, imagine a waterwheel. A pretty massive wheel (let's say 4 Tons), rotating lazily on a shaft. You determine that the wheel typically generated about 2600 foot-pounds of Torque, and it rotated at about 12 RPM. If you hooked that wheel to the drive wheels of a car, that car would go from zero to twelve RPM in a flash. But, 12 RPM at the drive wheels is around 1 MPH for the average car. In order to go faster, you'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot-pounds of Torque at the output, which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60. Applying the conversion formula 12 RPM * 2600/5252 = 6 HP. While it's clearly true that the water wheel can exert a lot of Force, its Power (ability to do work over time) is severely limited.

Happy Motoring!... Jim'99

[blue2000s]

Originally Posted by MNBoxster

Hi,

Yes, you are correct in pure physics, but in Autodom, and especially in the context of this thread, the term acceleration is, strictly speaking, misused and does imply a time component and work being done. You can generate 300 ft.-lbs. of Torque at 4000 RPM the instant the Clutch is released (from a dead stop), but the Car isn't yet doing any work.

There is really only Torque. Torque is the only thing that a driver feels, and Horsepower is just sort of an esoteric measurement in that context but adding in a time component.

300 foot-pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would double at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where Horsepower and Torque always come out the same.

In contrast to a Torque curve, Horsepower rises rapidly with RPM, especially when Torque values are also climbing. Horsepower will continue to climb, however, until well past the Torque peak, and will continue to rise as engine speed climbs, until the Torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver feels.

It is better to make torque at high rpm than at low rpm, because you can take advantage of gearing.

An extreme example of this, imagine a waterwheel. A pretty massive wheel (let's say 4 Tons), rotating lazily on a shaft. You determine that the wheel typically generated about 2600 foot-pounds of Torque, and it rotated at about 12 RPM. If you hooked that wheel to the drive wheels of a car, that car would go from zero to twelve RPM in a flash. But, 12 RPM at the drive wheels is around 1 MPH for the average car. In order to go faster, you'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot-pounds of Torque at the output, which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60. Applying the conversion formula 12 RPM * 2600/5252 = 6 HP. While it's clearly true that the water wheel can exert a lot of Force, its Power (ability to do work over time) is severely limited.

Happy Motoring!... Jim'99

Acceleration ALWAYS includes the element of time. It's m/s^2 after all.

You are still talking about torque, but trying to glean some extra information from the power curve, which I'd warn is not always accurate. I'm really not sure what else to tell you but take a look at the text that I cited above. It's only concerned with "autodom". The equations used to calculate acceleration (very accurately, I might add) don't have power in them.

[blue2000s]

Originally Posted by MNBoxster

Hi,

Yes, you are correct in pure physics, but in Autodom, and especially in the context of this thread, the term acceleration is, strictly speaking, misused and does imply a time component and work being done. You can generate 300 ft.-lbs. of Torque at 4000 RPM the instant the Clutch is released (from a dead stop), but the Car isn't yet doing any work.

There is really only Torque. Torque is the only thing that a driver feels, and Horsepower is just sort of an esoteric measurement in that context but adding in a time component.

300 foot-pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would double at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where Horsepower and Torque always come out the same.

In contrast to a Torque curve, Horsepower rises rapidly with RPM, especially when Torque values are also climbing. Horsepower will continue to climb, however, until well past the Torque peak, and will continue to rise as engine speed climbs, until the Torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver feels.

It is better to make torque at high rpm than at low rpm, because you can take advantage of gearing.

An extreme example of this, imagine a waterwheel. A pretty massive wheel (let's say 4 Tons), rotating lazily on a shaft. You determine that the wheel typically generated about 2600 foot-pounds of Torque, and it rotated at about 12 RPM. If you hooked that wheel to the drive wheels of a car, that car would go from zero to twelve RPM in a flash. But, 12 RPM at the drive wheels is around 1 MPH for the average car. In order to go faster, you'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot-pounds of Torque at the output, which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60. Applying the conversion formula 12 RPM * 2600/5252 = 6 HP. While it's clearly true that the water wheel can exert a lot of Force, its Power (ability to do work over time) is severely limited.

Happy Motoring!... Jim'99

http://vettenet.org/torquehp.html

It's a good idea to cite your references for information.

[insite]

Originally Posted by blue2000s

Wow. Don't confuse torque with power, they're directly related but totally different and can't be used like this.

If you go back to the fundamentals, force=mass*acceleration, torque is a twisting force. It can be directly calculated to force by the wheel/tire radius, therefore it is the property that defines acceleration.

blue - you're missing some things. unfortunately in our goofy measuring units, it's simple to do. MNBoxster is spot on. a ft-lb is a unit of work. a lb-ft is a unit of force.

[blue2000s]

Originally Posted by insite

blue - you're missing some things. unfortunately in our goofy measuring units, it's simple to do. MNBoxster is spot on. a ft-lb is a unit of work. a lb-ft is a unit of force.

What am I missing?

[blue2000s]

Originally Posted by MNBoxster

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...

Agreed, but power doesn't give you this story. The torque curve does.