Shift Points for Maximum 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.

[MNBoxster]

Originally Posted by blue2000s

http://vettenet.org/torquehp.html

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

Hi,

Interesting, but this wasn't my source. This must have been posted on numerous sites, because I have seen it before...

Happy Motoring!... Jim'99

[Brad Roberts]

My point is:

Keep talking it about and applying science. I'm going to go and actually do it.

It's cool. I know where you are coming from I also fully understand the theory. I spend a lot of time applying the theory to AutoX and road racing where I need torque. I dont really give a sh_t about it on the street where 90% of these people drive their Boxsters.

Case in point (I have done this in the past multiple times)

We both line up side by side in the same cars on the same tires. You apply torque theory to the drag race about to occur between us. I beat you from experience, not theory. Everything works on paper.

My engines make the most power in the computer simulation software I use!!


B

[denverpete]

Originally Posted by MNBoxster

Hi,

Interesting, but this wasn't my source. This must have been posted on numerous sites, because I have seen it before...

Happy Motoring!... Jim'99

Pretty verbatim to your post though.....

[Brad Roberts]

Copy and paste?


B

[MNBoxster]

Originally Posted by denverpete

Pretty verbatim to your post though.....

Hi,

I most likely found this some time ago, thought it contained several good points and I copied it as a Word document to the pretty large database on Car Stuff that I maintain.

Much of my reply was Cut & Paste from this, and other sources, it's much more efficient than transcribing it for this Forum. This is why I didn't quote a source, because I don't remember where I got it, the source is lost to me. I am certain it wasn't from a Corvette site, because I never visit them.

But, that doesn't make it any less true. None of the respondents to this and other technical threads invented any of this stuff, we're merely passing on the information we have available.

I am an author by trade (have done a lot of Ghost Writing and technical editing for several publishers, including Motorbooks Int'l.) and pay particular attention to quoting sources and giving footnote credits and have often done so here. I must regularly review my work to insure that no plagerism has occured and I am experienced in doing so. But, I don't give a foornote credit to the guy who invented the word The. And, I'm sure that you realize that pretty verbatim is not verbatim. I don't see a foul if that's what blue2000s is trying to imply...

Happy Motoring!... Jim'99

[blue2000s]

Originally Posted by MNBoxster

And, I'm sure that you realize that pretty verbatim is not verbatim. I don't see a foul if that's what blue2000s is trying to imply...

Happy Motoring!... Jim'99

I'm actually not tyring to impy that at all. Although I'm sure you know that plagerization isn't just copying someone else word for word.

My point is that I can't have a conversation with an internet article and if that's the dimension of this converse, it's dissapointing and pretty much pointless.