FWHP vs RWHP
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Joined: Jan 2002
Posts: 5,308
From: Oshawa - Home of the 5th-gen
A very general figure for drivetrain loss is 15%. It can truly range anywhere from 10% upto 25%, but it will normally be less for a manual transmission car
. SO, let's say hypothetically your LT1 is making ~400 HP (at the flywheel) and the drivetrain loss is ~15%. The rear-wheel HP would then be:
400 FWHP X .85 = 340 RWHP
(remember that .85 is 1 minus the % loss written as a decimal, so 1 - .15 ).
However, the loss may only be ~12%, in which case the RWHP would be 400 X .88 = 352 HP
.
. SO, let's say hypothetically your LT1 is making ~400 HP (at the flywheel) and the drivetrain loss is ~15%. The rear-wheel HP would then be:400 FWHP X .85 = 340 RWHP
(remember that .85 is 1 minus the % loss written as a decimal, so 1 - .15 ).
However, the loss may only be ~12%, in which case the RWHP would be 400 X .88 = 352 HP
.
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Joined: May 2002
Posts: 1,475
Originally posted by Capn Pete
A very general figure for drivetrain loss is 15%. It can truly range anywhere from 10% upto 25%, but it will normally be less for a manual transmission car. SO, let's say hypothetically your LT1 is making ~400 HP (at the flywheel) and the drivetrain loss is ~15%. The rear-wheel HP would then be:
400 FWHP X .85 = 340 RWHP
(remember that .85 is 1 minus the % loss written as a decimal, so 1 - .15 ).
However, the loss may only be ~12%, in which case the RWHP would be 400 X .88 = 352 HP.
A very general figure for drivetrain loss is 15%. It can truly range anywhere from 10% upto 25%, but it will normally be less for a manual transmission car
. SO, let's say hypothetically your LT1 is making ~400 HP (at the flywheel) and the drivetrain loss is ~15%. The rear-wheel HP would then be:400 FWHP X .85 = 340 RWHP
(remember that .85 is 1 minus the % loss written as a decimal, so 1 - .15 ).
However, the loss may only be ~12%, in which case the RWHP would be 400 X .88 = 352 HP
.
Thnx
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Joined: Mar 2000
Posts: 2,037
From: 51°N 114°W, 3500' elevation
Flywheel HP and Rear Wheel HP.
A percentage is a poor way of measuring it but everyone does it.
If you have a 400hp engine and it loses 15% through the driveline then only 340hp get to the rear wheels.
Now take the same car and drop in a 600hp engine. Losing 15% through the driveline means instead of losing 60hp, you lose 90hp. How did you lose an additional 30hp through the driveline when all that was changed was the engine?
Flywheel hp means nothing except bragging rights. You don't race just an engine but the whole car. What gets to the rear wheels is all that matters. A lower hp engine that can get more power to the rear wheels will be faster.
A percentage is a poor way of measuring it but everyone does it.
If you have a 400hp engine and it loses 15% through the driveline then only 340hp get to the rear wheels.
Now take the same car and drop in a 600hp engine. Losing 15% through the driveline means instead of losing 60hp, you lose 90hp. How did you lose an additional 30hp through the driveline when all that was changed was the engine?
Flywheel hp means nothing except bragging rights. You don't race just an engine but the whole car. What gets to the rear wheels is all that matters. A lower hp engine that can get more power to the rear wheels will be faster.
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Joined: May 2002
Posts: 1,475
Originally posted by Camaro_Guru16NY
FWD sucks rear wheel all the way.
Cool Formula though.
-John
FWD sucks rear wheel all the way.
Cool Formula though.
-John
Originally posted by PhatT/A
he is reffering to FrontWheel HORSE POWER...NOT FrontWheel DRIVE
he is reffering to FrontWheel HORSE POWER...NOT FrontWheel DRIVE
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Joined: Jan 2002
Posts: 5,308
From: Oshawa - Home of the 5th-gen
Originally posted by Stephen 87 IROC
Flywheel HP and Rear Wheel HP.
A percentage is a poor way of measuring it but everyone does it.
If you have a 400hp engine and it loses 15% through the driveline then only 340hp get to the rear wheels.
Now take the same car and drop in a 600hp engine. Losing 15% through the driveline means instead of losing 60hp, you lose 90hp. How did you lose an additional 30hp through the driveline when all that was changed was the engine?
Flywheel HP and Rear Wheel HP.
A percentage is a poor way of measuring it but everyone does it.
If you have a 400hp engine and it loses 15% through the driveline then only 340hp get to the rear wheels.
Now take the same car and drop in a 600hp engine. Losing 15% through the driveline means instead of losing 60hp, you lose 90hp. How did you lose an additional 30hp through the driveline when all that was changed was the engine?
. For a stock car, I think it's safe to say that there is roughly a 15% loss, but really, that loss can be translated into an actual amount of horsepower required, which should be constant no matter what (or almost constant) so theoretically, a 600 HP engine in place of the 400 HP engine that lost 60 HP through the drivetrain should still only lose ~60 HP, and therefore make roughly 540 HP at the wheels
. 540 RWHP / 600 FWHP = only a 10% loss .
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Posts: 71,115
From: Hell was full so they sent me to NJ
A percentage isn't all that bad a way to APPROXIMATE it.
It is very easy to demonstrate that drivetrain loss consists of both a "fixed" (inertia related) and a "variable" (friction related) component. If you keep the drivetrain the same, the inertia losses of bringing the rotating components up to speed is a constant, ASSUMING the rate at which the revs increase it held constant. It can be demonstrated that this component of loss is typically less than 20HP. That part won't change when you up the flywheel HP.
But the "variable" component is a true percentage (at least in the manual tranny case), and it changes with engine HP because it is mainly friction... in bearings and on gear surfaces. Increase the torque from the engine, and you increase the forces acting on the bearings and gears. Increase the loads and you increase friction losses proportionally.... a direct percentage.
I have the actual drivetrain loss for my setup, arrived at by comparing engine dyno numbers with chassis dyno numbers.
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
And... performance is not all that dependant on "rear wheel" HP. While the TH400 showed a huge loss of rwHP (35 less rwHP at 500fwHP, 70 less rwHP at 765fwHP), the ability of the torque convertor to provide the huge initial torque multiplication, and the ability of the high stall to keep the revs up in the "sweet spot" of the torque curve were enough to offset the rwHP loss. Performance did not appear to suffer appreciably.
It is very easy to demonstrate that drivetrain loss consists of both a "fixed" (inertia related) and a "variable" (friction related) component. If you keep the drivetrain the same, the inertia losses of bringing the rotating components up to speed is a constant, ASSUMING the rate at which the revs increase it held constant. It can be demonstrated that this component of loss is typically less than 20HP. That part won't change when you up the flywheel HP.
But the "variable" component is a true percentage (at least in the manual tranny case), and it changes with engine HP because it is mainly friction... in bearings and on gear surfaces. Increase the torque from the engine, and you increase the forces acting on the bearings and gears. Increase the loads and you increase friction losses proportionally.... a direct percentage.
I have the actual drivetrain loss for my setup, arrived at by comparing engine dyno numbers with chassis dyno numbers.
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
And... performance is not all that dependant on "rear wheel" HP. While the TH400 showed a huge loss of rwHP (35 less rwHP at 500fwHP, 70 less rwHP at 765fwHP), the ability of the torque convertor to provide the huge initial torque multiplication, and the ability of the high stall to keep the revs up in the "sweet spot" of the torque curve were enough to offset the rwHP loss. Performance did not appear to suffer appreciably.
Last edited by Injuneer; Feb 4, 2004 at 12:42 AM.
Thread Starter
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Joined: May 2002
Posts: 1,475
Originally posted by Injuneer
A percentage isn't all that bad a way to APPROXIMATE it.
It is very easy to demonstrate that drivetrain loss consists of both a "fixed" (inertia related) and a "variable" (friction related) component. If you keep the drivetrain the same, the inertia losses of bringing the rotating components up to speed is a constant, ASSUMING the rate at which the revs increase it held constant. It can be demonstrated that this component of loss is typically less than 20HP. That part won't change when you up the flywheel HP.
But the "variable" component is a true percentage (at least in the manual tranny case), and it changes with engine HP because it is mainly friction... in bearings and on gear surfaces. Increase the torque from the engine, and you increase the forces acting on the bearings and gears. Increase the loads and you increase friction losses proportionally.... a direct percentage.
I have the actual drivetrain loss for my setup, arrived at by comparing engine dyno numbers with chassis dyno numbers.
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
And... performance is not all that dependant on "rear wheel" HP. While the TH400 showed a huge loss of rwHP (35 less rwHP at 500fwHP, 70 less rwHP at 765fwHP), the ability of the torque convertor to provide the huge initial torque multiplication, and the ability of the high stall to keep the revs up in the "sweet spot" of the torque curve were enough to offset the rwHP loss. Performance did not appear to suffer appreciably.
A percentage isn't all that bad a way to APPROXIMATE it.
It is very easy to demonstrate that drivetrain loss consists of both a "fixed" (inertia related) and a "variable" (friction related) component. If you keep the drivetrain the same, the inertia losses of bringing the rotating components up to speed is a constant, ASSUMING the rate at which the revs increase it held constant. It can be demonstrated that this component of loss is typically less than 20HP. That part won't change when you up the flywheel HP.
But the "variable" component is a true percentage (at least in the manual tranny case), and it changes with engine HP because it is mainly friction... in bearings and on gear surfaces. Increase the torque from the engine, and you increase the forces acting on the bearings and gears. Increase the loads and you increase friction losses proportionally.... a direct percentage.
I have the actual drivetrain loss for my setup, arrived at by comparing engine dyno numbers with chassis dyno numbers.
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
And... performance is not all that dependant on "rear wheel" HP. While the TH400 showed a huge loss of rwHP (35 less rwHP at 500fwHP, 70 less rwHP at 765fwHP), the ability of the torque convertor to provide the huge initial torque multiplication, and the ability of the high stall to keep the revs up in the "sweet spot" of the torque curve were enough to offset the rwHP loss. Performance did not appear to suffer appreciably.
Is it that bad even with the stock autos? Makes me glad I have a 6 speed
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Joined: May 2001
Posts: 97
From: Reno, NV
Originally posted by Injuneer
A percentage isn't all that bad a way to APPROXIMATE it.
It is very easy to demonstrate that drivetrain loss consists of both a "fixed" (inertia related) and a "variable" (friction related) component. If you keep the drivetrain the same, the inertia losses of bringing the rotating components up to speed is a constant, ASSUMING the rate at which the revs increase it held constant. It can be demonstrated that this component of loss is typically less than 20HP. That part won't change when you up the flywheel HP.
But the "variable" component is a true percentage (at least in the manual tranny case), and it changes with engine HP because it is mainly friction... in bearings and on gear surfaces. Increase the torque from the engine, and you increase the forces acting on the bearings and gears. Increase the loads and you increase friction losses proportionally.... a direct percentage.
I have the actual drivetrain loss for my setup, arrived at by comparing engine dyno numbers with chassis dyno numbers.
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
And... performance is not all that dependant on "rear wheel" HP. While the TH400 showed a huge loss of rwHP (35 less rwHP at 500fwHP, 70 less rwHP at 765fwHP), the ability of the torque convertor to provide the huge initial torque multiplication, and the ability of the high stall to keep the revs up in the "sweet spot" of the torque curve were enough to offset the rwHP loss. Performance did not appear to suffer appreciably.
A percentage isn't all that bad a way to APPROXIMATE it.
It is very easy to demonstrate that drivetrain loss consists of both a "fixed" (inertia related) and a "variable" (friction related) component. If you keep the drivetrain the same, the inertia losses of bringing the rotating components up to speed is a constant, ASSUMING the rate at which the revs increase it held constant. It can be demonstrated that this component of loss is typically less than 20HP. That part won't change when you up the flywheel HP.
But the "variable" component is a true percentage (at least in the manual tranny case), and it changes with engine HP because it is mainly friction... in bearings and on gear surfaces. Increase the torque from the engine, and you increase the forces acting on the bearings and gears. Increase the loads and you increase friction losses proportionally.... a direct percentage.
I have the actual drivetrain loss for my setup, arrived at by comparing engine dyno numbers with chassis dyno numbers.
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
And... performance is not all that dependant on "rear wheel" HP. While the TH400 showed a huge loss of rwHP (35 less rwHP at 500fwHP, 70 less rwHP at 765fwHP), the ability of the torque convertor to provide the huge initial torque multiplication, and the ability of the high stall to keep the revs up in the "sweet spot" of the torque curve were enough to offset the rwHP loss. Performance did not appear to suffer appreciably.
This should be spread around to everybody that thinks it is a % or a number that does not change.
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Joined: Jan 2002
Posts: 5,308
From: Oshawa - Home of the 5th-gen
Originally posted by Injuneer
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
For a Street Twin (steel FW), T56, 3" chrome moly DS and Strange 12-bolt with 3.73 gears, the drivetrain loss was:
500fwHP = 12.6% loss
635fwHP = 12.3% loss
765fwHP = 12.1% loss
Swapping in the TH400, loose, high stall non-locking convertor caused a major increase in drivetrain loss:
500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%
The % loss decreased with HP increase for the 6-speed, but with the auto, the % loss increased along with HP?!
That (almost) doesn't make sense!?
While this does show that % loss can change with increasing power, it also shows that the difference is not all that much
.
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Joined: Mar 2000
Posts: 2,037
From: 51°N 114°W, 3500' elevation
Numbers I dug up a while ago.
HP loss through the tranny. The numbers are approximate since it depends on internal clearances and modifications. Lightweight aluminum clutch hubs and loose frictions will decrease the amount of loss. Using synthetic oil will reduce it even more. Even things like lowering the pump pressure can gain a few extra hp to the rear wheels.
Powerglide = 18 hp
TH350 = 36 hp
TH400 = 44 hp
HP loss through the tranny. The numbers are approximate since it depends on internal clearances and modifications. Lightweight aluminum clutch hubs and loose frictions will decrease the amount of loss. Using synthetic oil will reduce it even more. Even things like lowering the pump pressure can gain a few extra hp to the rear wheels.
Powerglide = 18 hp
TH350 = 36 hp
TH400 = 44 hp
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Joined: Aug 2000
Posts: 744
From: Columbia, SC
Originally posted by Capn Pete
That seems weird? The % loss decreased with HP increase for the 6-speed, but with the auto, the % loss increased along with HP?! That (almost) doesn't make sense!?
While this does show that % loss can change with increasing power, it also shows that the difference is not all that much.
That seems weird?
The % loss decreased with HP increase for the 6-speed, but with the auto, the % loss increased along with HP?! That (almost) doesn't make sense!?While this does show that % loss can change with increasing power, it also shows that the difference is not all that much
.