Power train loss HP vs Torque
04-30-2016, 12:25 PM
#1
Safety Car
Thread Starter
Power train loss HP vs Torque
You always hear power train loss for horsepower, whether it's 12% for manuals or 15% for autos between flywheel and rear wheels. Without getting into a percentage debate, is power train loss for torque at the rear wheels the same?
For example:
500 flywheel HP for manual = 440 hp at rear wheels (12% loss )
500 flywheel ft. lbs. torque for manual. What is the power train loss for torque at the wheels?
For example:
500 flywheel HP for manual = 440 hp at rear wheels (12% loss )
500 flywheel ft. lbs. torque for manual. What is the power train loss for torque at the wheels?
Last edited by Mike's LS3; 04-30-2016 at 01:00 PM.
04-30-2016, 08:38 PM
#5
Le Mans Master
Driveline loss should be a constant/set amount right (ie: 12% manuals)? So if you double the power of the engine....the Driveline doesn't turn twice as hard..... it still only takes the "said amount" to move the car forward. So I don't understand why it stated that Driveline loss is (12%) of any HP??
Example: if Driveline loss at 500hp is 60hp......then a 1000hp doesn't loss 120hp.....it is moving the same components....
Example: if Driveline loss at 500hp is 60hp......then a 1000hp doesn't loss 120hp.....it is moving the same components....
Last edited by C U IN REARVEIW; 04-30-2016 at 08:44 PM.
04-30-2016, 09:41 PM
#6
Safety Car
Thread Starter
Driveline loss should be a constant/set amount right (ie: 12% manuals)? So if you double the power of the engine....the Driveline doesn't turn twice as hard..... it still only takes the "said amount" to move the car forward. So I don't understand why it stated that Driveline loss is (12%) of any HP??
Example: if Driveline loss at 500hp is 60hp......then a 1000hp doesn't loss 120hp.....it is moving the same components....
Example: if Driveline loss at 500hp is 60hp......then a 1000hp doesn't loss 120hp.....it is moving the same components....
Last edited by Mike's LS3; 04-30-2016 at 09:44 PM.
05-01-2016, 10:04 AM
#7
Race Director
My experience with dyno runs and tuning shows the tq loss to be just about parallel with the hp loss.
Within a 1% anyway.
Now this is not taking into account big power modes at least not past the usual bolt ons.
So at 500 flywheel hp your rwtq would be around 440.
Within a 1% anyway.
Now this is not taking into account big power modes at least not past the usual bolt ons.
So at 500 flywheel hp your rwtq would be around 440.
05-01-2016, 03:21 PM
#8
Safety Car
Thread Starter
That's about what I figured, but you never hear about torque loss through the drive train, only horsepower loss.
Thanks Boomer!
05-01-2016, 08:42 PM
#10
Safety Car
Thread Starter
Let me simplify the answer:
1. Take a stock manual LS3 rated at the flywheel with 436 hp and 428 ft.lb torque.
2. Put the car on the dyno.
3. Dyno readings for a stock 6 speed manual LS3 will read about 12% less for both horsepower and torque at the wheels.
1. Take a stock manual LS3 rated at the flywheel with 436 hp and 428 ft.lb torque.
2. Put the car on the dyno.
3. Dyno readings for a stock 6 speed manual LS3 will read about 12% less for both horsepower and torque at the wheels.
Last edited by Mike's LS3; 05-01-2016 at 08:53 PM.
05-01-2016, 09:17 PM
#11
Melting Slicks
Parasitic losses...
The fallowing is actual flywheel numbers for same engine max torque 695.3 max power 659.6
Chassis dyno numbers for same engine torque 604.6 power 573.6
Above car N/A A6 transmission about 13% torque loss and about 13% loss of horse power.
I have a supercharged motor made 1,110 torque to the crank and 940 to the tires but is not a corvette and different cars seem to have different losses true the drive train.
Chassis dyno numbers for same engine torque 604.6 power 573.6
Above car N/A A6 transmission about 13% torque loss and about 13% loss of horse power.
I have a supercharged motor made 1,110 torque to the crank and 940 to the tires but is not a corvette and different cars seem to have different losses true the drive train.
05-01-2016, 10:23 PM
#12
Drivetrain loss is not a set number ie. it only takes 60 HP to overcome drivetrain loss. That is incorrect.
Drivetrain loss is because mass takes energy to accelerate, and to increase the acceleration rate of any given mass, the larger the amount of energy is required to accelerate that mass.
So take the drive train loss of a 638hp car and compare the drive train loss of a 500hp car. Look up zr1 vs z06 dyno numbers and you will find a much larger drivetrain loss on the zr1 despite having lighter rotors on the rear brakes reducing the "drivetrain" mass a bit.
This is why % drivetrain loss is a "rule of thumb" concept which can apply VERY loosely.
Drivetrain loss is because mass takes energy to accelerate, and to increase the acceleration rate of any given mass, the larger the amount of energy is required to accelerate that mass.
So take the drive train loss of a 638hp car and compare the drive train loss of a 500hp car. Look up zr1 vs z06 dyno numbers and you will find a much larger drivetrain loss on the zr1 despite having lighter rotors on the rear brakes reducing the "drivetrain" mass a bit.
This is why % drivetrain loss is a "rule of thumb" concept which can apply VERY loosely.
05-01-2016, 10:24 PM
#13
Driveline loss should be a constant/set amount right (ie: 12% manuals)? So if you double the power of the engine....the Driveline doesn't turn twice as hard..... it still only takes the "said amount" to move the car forward. So I don't understand why it stated that Driveline loss is (12%) of any HP??
Example: if Driveline loss at 500hp is 60hp......then a 1000hp doesn't loss 120hp.....it is moving the same components....
Example: if Driveline loss at 500hp is 60hp......then a 1000hp doesn't loss 120hp.....it is moving the same components....
So by that logic if I would hook a 59hp motor up to your hypothetical drive train then that 59hp motor wouldn't turn the drive train? Doubtful. IMO the faster you try to turn something the more resistance it gives you and takes more hp to turn. I don't buy the flat hp loss from drive train argument.
05-01-2016, 10:37 PM
#14
I'll just toss in F=ma or rather a = F/m.
F -> Force
m -> mass
a ->acceleration
To look at this in the simplest terms, a is acceleration which is linked to hp. If you want to increase your accleration/hp value, then more force is needed, they go hand in hand. So the force needed to accelerate the mass of the drivetrain goes up hand in hand with the acceleration increase you are going for.
So you want the car to go faster in a quicker (shorten the time to cover the same distance ie 1/4 mile) then the requirements to accelerate EVERYTHING, including spinning a driveshaft/wheels etc go up hand in hand.
F -> Force
m -> mass
a ->acceleration
To look at this in the simplest terms, a is acceleration which is linked to hp. If you want to increase your accleration/hp value, then more force is needed, they go hand in hand. So the force needed to accelerate the mass of the drivetrain goes up hand in hand with the acceleration increase you are going for.
So you want the car to go faster in a quicker (shorten the time to cover the same distance ie 1/4 mile) then the requirements to accelerate EVERYTHING, including spinning a driveshaft/wheels etc go up hand in hand.
05-02-2016, 09:11 AM
#15
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St. Jude Donor '15
Slade is right. It takes more energy to spin something up faster
05-02-2016, 10:57 AM
#16
Melting Slicks
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St. Jude Donor '10-'11-'12-'13-'14
Remember that torque is nothing more than horsepower at a given rpm (or vice versa, if you prefer). In fact a dyno measures torque and rpm, and uses a formula to show corresponding horsepower.
So in a sense torque and horsepower are the same thing, and therefore would show the same driveline loss.
So in a sense torque and horsepower are the same thing, and therefore would show the same driveline loss.
05-02-2016, 05:31 PM
#17
Safety Car
Thread Starter
Remember that torque is nothing more than horsepower at a given rpm (or vice versa, if you prefer). In fact a dyno measures torque and rpm, and uses a formula to show corresponding horsepower.
So in a sense torque and horsepower are the same thing, and therefore would show the same driveline loss.
So in a sense torque and horsepower are the same thing, and therefore would show the same driveline loss.
I did not want to get into a drivetrain loss % debate, but rather how the dyno measures both horsepower and torque.
Thanks to all who replied and sorry to those who were confused.
Last edited by Mike's LS3; 05-02-2016 at 05:34 PM.
05-02-2016, 08:34 PM
#18
Racer
OP, the calculation:
hp = torque * rpm / 5252
The Dyno measures torque and wheel/engine speed, horsepower is calculated from that.
So any drivetrain loss was measured as reduced wheel torque and caries through into the computed horsepower.
hp = torque * rpm / 5252
The Dyno measures torque and wheel/engine speed, horsepower is calculated from that.
So any drivetrain loss was measured as reduced wheel torque and caries through into the computed horsepower.
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