Drivetrain Loss as % not Constant ?
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 773
Likes: 7
From: wichita ks
Drivetrain Loss as % not Constant ?
I've been Driving Vettes since 1984 and Performance Cars since the 70's.
Have never been able to wrap my head around the % idea .
Getting older but maybe not wiser.
A transmission coupled to a differential and a couple of hubs holding the wheels and tires on.
If a 100 hp engine is able to turn the entire setup to 200mph,
How is it possible that a 1500hp engine can have a loss off 200+ hp?
Back in the late 90's I wanted to put Lingenfelter Twin Turbos on my 1998 Pace Car.
Around that time the Founder made a statement that the C5 manual configuration had loss of approx. 50 hp regardless of which upgrade was being added to the car ..500-650 hp packages .
Flamesuit on.
Have never been able to wrap my head around the % idea .
Getting older but maybe not wiser.
A transmission coupled to a differential and a couple of hubs holding the wheels and tires on.
If a 100 hp engine is able to turn the entire setup to 200mph,
How is it possible that a 1500hp engine can have a loss off 200+ hp?
Back in the late 90's I wanted to put Lingenfelter Twin Turbos on my 1998 Pace Car.
Around that time the Founder made a statement that the C5 manual configuration had loss of approx. 50 hp regardless of which upgrade was being added to the car ..500-650 hp packages .
Flamesuit on.
Racer
Joined: Mar 2011
Posts: 449
Likes: 8
From: Hayes Virginia
The new C7 has about a 11% loss with the M7 transmission and 12-13% loss with the A6 or A8.
I am sure someone else with more knowledge on the subject will chime in soon. I hope this helps answer your question..
Racer
Joined: Nov 2014
Posts: 418
Likes: 34
From: Kissimmee Florida
St. Jude Donor '16
I think what the op is saying is why isn't the hp loss a constant number instead of a percent.
Like if it takes 50hp on a 500hp car to turn the gears transmission etc.Then why would the 1500hp not be 1450hp at the wheels on the same car.
I believe that the percent is closer to the real number.As HP or torque increases then gears contact harder,More slip in torque converters,more pressure on bearing etc.
Causing more loss to the wheels.
Which results in a greater HP loss but almost the same percentage as the car with less hp.
Is it exact no.But it's a good guess.
Like if it takes 50hp on a 500hp car to turn the gears transmission etc.Then why would the 1500hp not be 1450hp at the wheels on the same car.
I believe that the percent is closer to the real number.As HP or torque increases then gears contact harder,More slip in torque converters,more pressure on bearing etc.
Causing more loss to the wheels.
Which results in a greater HP loss but almost the same percentage as the car with less hp.
Is it exact no.But it's a good guess.
Last edited by Warship2k15; Dec 30, 2014 at 05:29 AM.
Pro
Joined: May 2007
Posts: 511
Likes: 12
From: Parkville Maryland
This is an interesting read.
http://www.superstreetonline.com/how...in-power-loss/
I am curious now too... havent read the entire article yet but it made me think.
If you apply a set amount of force to a part, golf club to golf ball for example, and it goes a certain distance, you transferred x amount of force to that object.
Now you double the force but you dont double the distance, where did the extra energy go and how much force was actually transferred to that object?
http://www.superstreetonline.com/how...in-power-loss/
I am curious now too... havent read the entire article yet but it made me think.
If you apply a set amount of force to a part, golf club to golf ball for example, and it goes a certain distance, you transferred x amount of force to that object.
Now you double the force but you dont double the distance, where did the extra energy go and how much force was actually transferred to that object?
Melting Slicks
Joined: Jun 2012
Posts: 2,226
Likes: 1,029
From: Thomas Texas
This is best article I've read on the subject. I never understood the % loss quoted since the drive train could be exactly the same on a 300hp car and a 700hp car yet the % loss would be different.
I have said for a while, compare apples to apples or chassis dyno numbers to chassis dyn number and don't try gross them up to flywheel hp because it will rarely be right.
Here is the conclusion:
"So rather than attempting to convert your vehicle's dyno-measured wheel horsepower to a SAE net horsepower figure using a percentage or a fixed horsepower value, you're far better off accepting the fact that these two types of horsepower measurements aren't easily correlated and forego any attempt at doing so."
I have said for a while, compare apples to apples or chassis dyno numbers to chassis dyn number and don't try gross them up to flywheel hp because it will rarely be right.
Here is the conclusion:
"So rather than attempting to convert your vehicle's dyno-measured wheel horsepower to a SAE net horsepower figure using a percentage or a fixed horsepower value, you're far better off accepting the fact that these two types of horsepower measurements aren't easily correlated and forego any attempt at doing so."
Pro
Joined: Oct 2008
Posts: 606
Likes: 7
From: Nashville, TN
This is an interesting read.
http://www.superstreetonline.com/how...in-power-loss/
I am curious now too... havent read the entire article yet but it made me think.
If you apply a set amount of force to a part, golf club to golf ball for example, and it goes a certain distance, you transferred x amount of force to that object.
Now you double the force but you dont double the distance, where did the extra energy go and how much force was actually transferred to that object?
http://www.superstreetonline.com/how...in-power-loss/
I am curious now too... havent read the entire article yet but it made me think.
If you apply a set amount of force to a part, golf club to golf ball for example, and it goes a certain distance, you transferred x amount of force to that object.
Now you double the force but you dont double the distance, where did the extra energy go and how much force was actually transferred to that object?
Le Mans Master
Joined: Nov 1999
Posts: 7,695
Likes: 51
From: Imperial Beach CA
Using a percentage would work if you were not using lubrication. When using lubrication the calculation is more complex in that coefficient of friction now has to be considered. The use of a basic explanation, does the percentage change if the 1000hp engine is only operating at 500hp, therefore nonlinear.
Pro
Joined: Mar 2013
Posts: 742
Likes: 154
Much of the drivetrain loss comes from friction.
Friction is most simply approximated as the coefficient of friction multiplied by the normal force. On gears, the normal force is proportional to torque, so it follows that the friction will also be proportional to torque. Therefore, drivetrain frictional losses are typically approximated by a factor proportional to torque - in this case, a % loss.
The friction component can be broken down in more details, but typically the most significant factors are proportional to load, hence the % loss estimate.
It isn't perfect, but it does make some sense. Just don't try to use a dyno number as fact, equate it to a flywheel number, and then conclude that the drivetrain loss is that specific conversion factor. Dynos all read slightly differently, especially as conditions change, so it's really best to always use the same dyno and to compare gains from a baseline number rather than simply look at the final output.
-T
Friction is most simply approximated as the coefficient of friction multiplied by the normal force. On gears, the normal force is proportional to torque, so it follows that the friction will also be proportional to torque. Therefore, drivetrain frictional losses are typically approximated by a factor proportional to torque - in this case, a % loss.
The friction component can be broken down in more details, but typically the most significant factors are proportional to load, hence the % loss estimate.
It isn't perfect, but it does make some sense. Just don't try to use a dyno number as fact, equate it to a flywheel number, and then conclude that the drivetrain loss is that specific conversion factor. Dynos all read slightly differently, especially as conditions change, so it's really best to always use the same dyno and to compare gains from a baseline number rather than simply look at the final output.
-T
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Melting Slicks
Joined: Jan 2010
Posts: 2,205
Likes: 67
From: Cumming GA
Much of the drivetrain loss comes from friction.
Friction is most simply approximated as the coefficient of friction multiplied by the normal force. On gears, the normal force is proportional to torque, so it follows that the friction will also be proportional to torque. Therefore, drivetrain frictional losses are typically approximated by a factor proportional to torque - in this case, a % loss.
The friction component can be broken down in more details, but typically the most significant factors are proportional to load, hence the % loss estimate.
It isn't perfect, but it does make some sense. Just don't try to use a dyno number as fact, equate it to a flywheel number, and then conclude that the drivetrain loss is that specific conversion factor. Dynos all read slightly differently, especially as conditions change, so it's really best to always use the same dyno and to compare gains from a baseline number rather than simply look at the final output.
-T
Friction is most simply approximated as the coefficient of friction multiplied by the normal force. On gears, the normal force is proportional to torque, so it follows that the friction will also be proportional to torque. Therefore, drivetrain frictional losses are typically approximated by a factor proportional to torque - in this case, a % loss.
The friction component can be broken down in more details, but typically the most significant factors are proportional to load, hence the % loss estimate.
It isn't perfect, but it does make some sense. Just don't try to use a dyno number as fact, equate it to a flywheel number, and then conclude that the drivetrain loss is that specific conversion factor. Dynos all read slightly differently, especially as conditions change, so it's really best to always use the same dyno and to compare gains from a baseline number rather than simply look at the final output.
-T
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Depending on the extensive fabrication on a race car--builders can reduce " drivetrain loss" to make it less ending up with more RWHP
As the new Corvettes have developed the sane rules apply---The C7 manual has now the least drivetrain loss than ever before (under 10%) and the new A6-A8 automatics are now about 10-12%---The manuals only show minor RWHP gains but the new automatics RWHP gains have gone from an average of -20-22% to a low - 12% !!! that is huge---Making an automatic almost equal to RWHP to a manual ---
LESS Friction is a major reason for the increases---as well as the new Clutch to Clutch TQ converter--
As the new Corvettes have developed the sane rules apply---The C7 manual has now the least drivetrain loss than ever before (under 10%) and the new A6-A8 automatics are now about 10-12%---The manuals only show minor RWHP gains but the new automatics RWHP gains have gone from an average of -20-22% to a low - 12% !!! that is huge---Making an automatic almost equal to RWHP to a manual ---
LESS Friction is a major reason for the increases---as well as the new Clutch to Clutch TQ converter--
Le Mans Master
Joined: Aug 2000
Posts: 5,529
Likes: 1,943
From: Austin Texas
the 300 HP car takes 7 seconds to accelerate the speed differential that the 700 HP car only takes 3 seconds to accelerate.
While the driveline might be made of the same components, the stress levels in the gears, bearings, and cases are far, far different (2.33 = 7/3 n the given example).