Shift Points for Maximum Acceleration

[986Jim]

Except for the fact that this doesn't acctually work in real life.

Try this at the track with Any car, no matter what it is. If you shift where your torque is at the maximum instead of redline you will always run a slower 1/4 mile time. This is a pretty old myth and one that I fell into myself when I first started drag racing.

I have drag raced about 8 different cars in the last 15 years pretty hard core, right into the 10's in a few of them. They have all been to the dyno, and I have tried shifting them all at peak torque like this graph illustrates. If you shift at peak torque you simply go slower every time.

Your always better to shift at your highest RPM point. As the RPM falls back down, it doesn't matter that it's over the Torque peak when you shift, it's that you land in a higher RPM point when you did the shift into the next gear. The higher you land in the RPM band after your shift the faster the engine will accelerate. If you shift at 5500rpm and fall to 3500rpm you car will be slower than shifting at 6500rpm and landing at 4500rpm because the engine will rev easier and faster to 6500rpm again from 4500rpm faster than 3500rpm to 5500rpm regardless of what your torque numbers are on a graph.

The best illustration of this is with a motorcycle. My CBR did 11.4 @ 126mph. It revs to 15,000rpm but peak HP is 13,000rpm, peak torque was 9000rpm or so. It was significantly slower if I shifted at anything less than absolute redline. The difference was a few 1/10ths and would knock me back to high 11's each time I messed with the shift points. Even in first gear, short shifting the bike made it slower. I did it however because I had to worry about poppin the wheel up hittin second without the clutch at 50mph.

Cool graph, but doens't pan out in real life. Don't take my word for it however, if you want proof hit up some hardcore drag racing forums and ask them this there. Their response will be much the same as what I just told you.

[blue2000s]

Originally Posted by 986Jim

Except for the fact that this doesn't acctually work in real life.

Try this at the track with Any car, no matter what it is. If you shift where your torque is at the maximum instead of redline you will always run a slower 1/4 mile time. This is a pretty old myth and one that I fell into myself when I first started drag racing.

I have drag raced about 8 different cars in the last 15 years pretty hard core, right into the 10's in a few of them. They have all been to the dyno, and I have tried shifting them all at peak torque like this graph illustrates. If you shift at peak torque you simply go slower every time.

Your always better to shift at your highest RPM point. As the RPM falls back down, it doesn't matter that it's over the Torque peak when you shift, it's that you land in a higher RPM point when you did the shift into the next gear. The higher you land in the RPM band after your shift the faster the engine will accelerate. If you shift at 5500rpm and fall to 3500rpm you car will be slower than shifting at 6500rpm and landing at 4500rpm because the engine will rev easier and faster to 6500rpm again from 4500rpm faster than 3500rpm to 5500rpm regardless of what your torque numbers are on a graph.

The best illustration of this is with a motorcycle. My CBR did 11.4 @ 126mph. It revs to 15,000rpm but peak HP is 13,000rpm, peak torque was 9000rpm or so. It was significantly slower if I shifted at anything less than absolute redline. The difference was a few 1/10ths and would knock me back to high 11's each time I messed with the shift points. Even in first gear, short shifting the bike made it slower. I did it however because I had to worry about poppin the wheel up hittin second without the clutch at 50mph.

Cool graph, but doens't pan out in real life. Don't take my word for it however, if you want proof hit up some hardcore drag racing forums and ask them this there. Their response will be much the same as what I just told you.

I don't think that you completely understand what the graph is saying. For any given vehicle speed, the torque to the wheels is shown. You can see from the graph that the best place to shift pretty much IS redline. This information is accurate if it's read correctly.

[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.

[BuffaloBoxster]

Gnerally speaking any advantage you think you'd gain from short-shifting is negated by the fact that the gear you're going into is further down the powerband.

[blue2000s]

Originally Posted by BuffaloBoxster

Gnerally speaking any advantage you think you'd gain from short-shifting is negated by the fact that the gear you're going into is further down the powerband.

Actually you can shift into a gear that's higher in the power band but still not have a benefit in acceleration because the torque at the wheels is lower than if you'd stayed in the higher gear.

[blue2000s]

There's alot of confusion here.

Depending on the power band, there CAN be a benefit to short-shifting but it's not common in production passenger vehicles and clearly not the case with the Boxster. This is deliberately done by the designers.

I encourage anyone who's really interested in understanding this stuff to look up "Fundamentals of Vehicle Dynamics" by Thomas D. Gillespie.

[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

[blue2000s]

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.

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.

[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.

[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.

[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.

[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

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!