How much HP is lost?
Thread Starter
Burning Brakes
Joined: Jul 2005
Posts: 998
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From: Somewhere between the Red and the Rio Republic of Texas
How much HP is lost?
Is there a way to determine how much HP I'm losing between the engine and the wheels if I have an A4 transmission with a 1900 stall? I'm putting down 400 to the wheels and 396 in torque. Just wondering what the engine is actully producing. Thanks in advance for all the responses.
Instructor
Joined: Jan 2010
Posts: 156
Likes: 0
From: Long Sault Ontario
I've seen the following info posted a number of times:
General rule of thumb is:
15% drive train loss for manual 6 speed tranny's
20% drive train loss for auto's
There is this formula as well: remember you have to have your RWHP from the dyno in order to estimate your Crank HP
Auto/A4 is:
RWHP divided by .82 for Estimated Crank HP
Manual is:
RWHP dvivded by .86 to get the estimated CRANK HP
Short of using estimates, you need to yank the engine and find someone with a Dyno that can do actual flywheel HP.
General rule of thumb is:
15% drive train loss for manual 6 speed tranny's
20% drive train loss for auto's
There is this formula as well: remember you have to have your RWHP from the dyno in order to estimate your Crank HP
Auto/A4 is:
RWHP divided by .82 for Estimated Crank HP
Manual is:
RWHP dvivded by .86 to get the estimated CRANK HP
Short of using estimates, you need to yank the engine and find someone with a Dyno that can do actual flywheel HP.
Pro
Joined: Aug 2010
Posts: 545
Likes: 4
From: Calgary Alberta
Fixed amount is more realistic. Somewhere from 70-80 HP for a manual, figure higher for an automatic. One interesting note I read a while back was regarding the Pontiac Solstice GXP edition. The turbo charged automatic version had a quicker quarter mile time because the additional/constant load of the torque converter kept the turbo spooled up!
http://forums.corvetteforum.com/c5-t...figures-2.html
Now better put some popcorn on as this topic usually gets them going!
http://forums.corvetteforum.com/c5-t...figures-2.html
Now better put some popcorn on as this topic usually gets them going!
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Last edited by ZeeOSix; Apr 1, 2011 at 09:08 PM.
Instructor
Joined: Jun 2008
Posts: 233
Likes: 1
From: Austin Texas
Years ago my lab partner and I did some experiments to find out the drag coefficient of a car. We used an electric motor to spin the drivetrain while in neutral to isolate and remove it's losses from the Cd calculation using P=VI. Unfortunately it'll only get you close though. There's some tire deformation and contact patch friction that eats power too. How close are you trying to estimate?
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Melting Slicks
Joined: Dec 2006
Posts: 2,186
Likes: 2
From: Woodinville WA
Is there a way to determine how much HP I'm losing between the engine and the wheels if I have an A4 transmission with a 1900 stall? I'm putting down 400 to the wheels and 396 in torque. Just wondering what the engine is actully producing. Thanks in advance for all the responses.
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
This topic has been beat to death over the years. It's really more complicated than saying it's a "fixed loss" or it's a "percentage loss". In reality it's a combination of both with many factors involved.
A while ago I tried to model it best I could from a pure engineering aspect based on a stock C5 Z06 . Came up with 43% loss due to inertial spin-up rate and fixed drag friction losses, and 57% loss due to HP frictional load through the drive train. This was based on a stock rated 405 FWHP Z06 (with stock wheels/tires) doing a dyno pull from 2000 to 6500 RPM in 20 seconds.
The inertial spin-up losses will change if the size and weight of the tires change, or if you spin up the drive train at a faster rate over the same RPM range.
A rear wheel brake dyno would take the drive train inertial spin up losses out of the mix ... same as an engine brake dyno does. On the other hand, an inertial chassis dyno does somewhat simulate the car accelerating down the road in terms of drive line inertial spin up losses.
Here's a petty good in depth article about drive train losses:
http://www.modified.com/tech/modp-10...oss/index.html
A while ago I tried to model it best I could from a pure engineering aspect based on a stock C5 Z06 . Came up with 43% loss due to inertial spin-up rate and fixed drag friction losses, and 57% loss due to HP frictional load through the drive train. This was based on a stock rated 405 FWHP Z06 (with stock wheels/tires) doing a dyno pull from 2000 to 6500 RPM in 20 seconds.
The inertial spin-up losses will change if the size and weight of the tires change, or if you spin up the drive train at a faster rate over the same RPM range.
A rear wheel brake dyno would take the drive train inertial spin up losses out of the mix ... same as an engine brake dyno does. On the other hand, an inertial chassis dyno does somewhat simulate the car accelerating down the road in terms of drive line inertial spin up losses.
Here's a petty good in depth article about drive train losses:
http://www.modified.com/tech/modp-10...oss/index.html
Last edited by ZeeOSix; Apr 2, 2011 at 02:06 PM.
