Shift Points for Maximum Acceleration

[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!

[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.

[blue2000s]

Originally Posted by 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.

I really hate to argue with this statement because it's been covered already, but it's not correct. You could have an engine who's torque curve drops off dramatically after peak due to breathing issues or two gear ratios that are very close to each other and it would be beneficial to shift before redline.

Just looking at a horsepower/torque curve DOES NOT tell you when to shift. IT DOES NOT TELL YOU WHEN TO SHIFT! You have to look at gear ratios and speeds in gears, just as I've done for you guys.

Typically, however, you happen to be right, but without understanding why this is true, you won't always be right.