Shift Points for Maximum Acceleration

[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.

[Brad Roberts]

Waiting with baited breath to find out who wins this argument.

Nobody!

In the end: we will shift where we want to shift. I love engineers, and theory, but I live in a real world. What is on paper doesnt always work.

Some of us call it "seat of the pants". I call it "calibrated ass"

Old school: "Bubba" shift the truck just after the valves float!!


B

[blue2000s]

Originally Posted by Brad Roberts

I live in a real world. What is on paper doesnt always work.

In my experience, that's what the people say when they don't understand the theory. Engineering is all about the application of science to the "real world" and using it to make real products. This is relatively simple stuff that is 100% applicable to real life.

[just_me]

... because the torque multiplication effect of the gearbox works in your favor, since you get the torqgue multiplied by a ahigher number of revolutions equal to the ratio of the two gears).

Grant

Originally Posted by insite

redline is usually best. forget torque; you want to shift just after peak POWER, thus allowing revs to fall at or near the peak POWER range.

torque is nothing without motion (work). you can apply torque and never actually move the car (zero work). power describes the rate at which work can be performed (i.e. how quickly can you move a mass of n pounds a distance of x feet). when your car is at peak power, it is performing work at its fastest capable rate.

this is why jim986's real life experience shows him that best acceleration runs occur when you ignore the torque peak and use the power that the almighty RPM helps us generate.

[99Boxster]

Sorry guys but WTF are you talking about? Are you saying the harder I press the accellerator the faster my car goes?

[blue2000s]

Originally Posted by just_me

... because the torque multiplication effect of the gearbox works in your favor, since you get the torqgue multiplied by a ahigher number of revolutions equal to the ratio of the two gears).

Grant

I'm running out of ways to explain this folks. Acceleration comes from force, which is directly related to the torque at the wheels and the wheel radius. I'm trying to make it as understandable as possible. Like I said above, you CAN use power, but that's not the way it's traditionally done.

[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.

[insite]

Originally Posted by blue2000s

It doesn't sound like you're quite getting it either. Power and toque are directly related, you can't neglect one or the other. The statement you've made is not accurate in that the calculations of acceleration use torque becuase it's units are more directly converted to the units of acceleration. Make no mistake, it's TORQUE that's commonly used in the calculations for acceleration.

not true, you can apply torque without generating power. try applying 90 ft-lb of torque to a bolt that's torqued to 100. it won't move, but you are still applying a torque to it. you are doing no WORK, and are therefore producing no power.

[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.

[insite]

Originally Posted by blue2000s

I'm running out of ways to explain this folks. Acceleration comes from force, which is directly related to the torque at the wheels and the wheel radius. I'm trying to make it as understandable as possible. Like I said above, you CAN use power, but that's not the way it's traditionally done.

blue, this is not true. force means nothing without MOTION. force that causes motion is WORK. work performed quickly is POWER.

Example: you have 2 identical cars w/ different torque curves. both cars are currently making 300 ft-lb of torque.

Car A: Torque = 300 ft-lb, RPM = 8000, HP = 457
Car B: Torque = 300 ft-lb, RPM = 4000, HP = 228

now, as you stated earlier, because these cars are making equal torque, they are accelerating at equal rates. BUT, assuming 1:1 final drive: car A is doing this from 91 mph while car B is doing this from 45 mph. even though they are gaining speed at the same rates, car A is travelling MUCH faster because it is performing WORK at twice the rate (double the POWER).

it is a common misconception that shifting just above peak torque will yield fastest acceleration times. gearing allows us to take advantage of power, though, and the object is to do the WORK (i.e. move 3000 lb of car 1/4 mile) as quickly as possible. work / time = power.

[blue2000s]

Originally Posted by insite

not true, you can apply torque without generating power. try applying 90 ft-lb of torque to a bolt that's torqued to 100. it won't move, but you are still applying a torque to it. you are doing no WORK, and are therefore producing no power.

I don't think I said anything to the contrary. You're surely correct. My point is that the acceleration comes from torque. I don't think you'd disagree.

[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 insite

blue, this is not true. force means nothing without MOTION. force that causes motion is WORK. work performed quickly is POWER.

Example: you have 2 identical cars w/ different torque curves. both cars are currently making 300 ft-lb of torque.

Car A: Torque = 300 ft-lb, RPM = 8000, HP = 457
Car B: Torque = 300 ft-lb, RPM = 4000, HP = 228

now, as you stated earlier, because these cars are making equal torque, they are accelerating at equal rates. BUT, assuming 1:1 final drive: car A is doing this from 91 mph while car B is doing this from 45 mph. even though they are gaining speed at the same rates, car A is travelling MUCH faster because it is performing WORK at twice the rate (double the POWER).

it is a common misconception that shifting just above peak torque will yield fastest acceleration times. gearing allows us to take advantage of power, though, and the object is to do the WORK (i.e. move 3000 lb of car 1/4 mile) as quickly as possible. work / time = power.

I wouldn't argue against that at all. but the acceleration of the vehicle still comes from torque doesn't it? That's all I've been saying.

What you are saying is that there is an advantage to acceleration in extended speed, this is certainly true, but this is still due to the conversion of that speed to torque at the wheels through gearing. It all comes back to torque. READ THE BOOK!

[986Jim]

You guys can do all the math and internet jibba jabba you want, but the fact of the matter is you always shift at the highest RPM you possibly can, no matter what your torque curve looks like.

The engine accelerates faster at it's highest RPM regardless of HP. Your car will accelerate faster if you shift at redline even if your power is down lower. Talk about physics and engineering all you want.

When the lights drop the BS stops, and if you don't shift at redline your in second place. PERIOD.

Here is the dyno plot from my Dad's Maxima that he drag races. It has a VQ35DE in it (350Z motor) and makes a maximum of 259whp and 239ft/lbs of torque normally aspirated at the wheels (this isn't the max dyno plot just one of them I snapped. The car has cams and torque convert and headers etc few trick and stuff.

Look at the HP and torque curve. That says you should shift at 6200rpm. When he does that the car runs 13.3 @ 100mph or worse. When he shifts at 7200rpm as indicated on the dyno, the car is faster, best now 12.8 @ 106mph. Almost a half a second and in terms of racing thats a long time.

Acctually this dyno before I tuned the car (emanage ultimate) made 236whp and 219ft/lbs of torque. We picked up 21hp peak with my tuning. Between 6000-7000 power was dropping below 180whp and with timing and air fuel tuning I bumped it to what you see there. I made 60whp extra between 6000-7000rpm over stock with my tuning tricks on his car. It should run a 12.4-12.5 now I would think with 60whp extra in the top rpm range.