FWD Transmission losses
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The following makes for interesting reading. Posted By Alan @ AVA following a rolling road day which saw a number of Members from the MLR & there EVO's being run.
Note that the 40bhp refered to relates to transmited losses for a 4WD vehicle.
Hi
Thanks to all who came to the rolling road day,interesting chatting to you & seeing your cars & the various modifications,
generaly very impressive results from most tested.
I read the comments on flywheel estimates with interest.
To clarify our position
At the roller speed at which we are testing these cars the losses would be approx 40bhp.
To justify this consider the theory of the 24% loss.
A car tested produces 200bhp at the wheels,add a 24% to this &
we get an estimated flywheel figure of 248BHP.
The car is then modified & produces 400bhp at the wheels at the same roller speed & engine speed.We then add the 24% to this &
a figure of 496bhp is arrived at.
This means that as the BHP rises so does the loss figure.
As the rpm has remained the same this means that the loss is
also measured as a loss of torque.
That means that as the torque rises so do the losses.
However if it is accepted that a rise in torque would increase the
the actual loss then it must also be the case that an increase in the measured at the wheels torque would also result in an increase in the losses.
ie if you test in third gear you might get say 1000lbf of torque
in fourth you might expect 800lbf of torque
in fifth you might expect 600lbf of torque
whereas you might expect 1200lbf of torque in second
That would mean that the losses in second with a 24% loss applied will be higher than in fifth with 24% applied.
In fact what happens in real tests is that the power figures DROP in each higher gear,the opposite of the % theory.
Also if these losses exist then where is the power going?
It would have to be heat or noise,I can't say I have ever noticed any rise in transmission noise or had it reported to me.
Heat ? Using our earlier theoretical model with a 96BHP loss
that would mean approx the heat of 70 1 bar electric fires in your
transmission & tyres.
Also if this loss is an under power loss then the inertia test which uses run down times(rate of slowing down of the rolling road)
to work out a flywheel figure could not work as clearly both of our theoretical cars must have the same run down time.
Why?
Confusion I believe arises from the terminoligy used,
ie the losses called "transmission loss" would be better named as "transmited loss" which does not infer that the loss is in the transmission.
"Transmited loss" is made up of a number of factors largest of which is the power required to drive the rolling road & rises
in a non linear fashion with the roller speed.
ie higher speed(gear) higher loss at the wheels.
The % alluded to is in there as well but is probably very small
(1 to 3%)as a guess.
This theory unlike the % theory covers most of the anomilies that arise during testing.
It also explains why BHP at the wheels seems to vary from rolling road to rolling road as different gears used or different roller diameters give different hard to figure results.
To qualify this opinion I offer 24 years of rolling road operating,
testing over twenty thousand cars of all makes.
The 40BHP mentioned is an approximate loss is based on the power consumption of two sets of 20" rollers at the speed of testing approx 80mph.
Also to those who question the test method,as this is how you measure BHP not HP & being the method of succesfully testing of the twenty thousand cars mentioned I don't see the problem.
Inertia testing as you mentioned is faster however does not allow for stabilising of readings,boost,temp,gas annalysis etc
& does not IN MY OPINION offer you the consumer the best deal.
It has only become the "norm" with the fast computers & in recent years.We can do inertia testing but in most instances choose not to.
Loaded testing simulates the worst case scenario for the car ie 170mph,4 heavy mates,up a hill,into the wind.& therfore predicts the outcome that as a tuner you are responsible for,of whether the car will survive that encounter,tuning to less stringent criterea may appear to give better results but only in the the short term or for those who don't subject their car to all it is capable of.
It is also very repeatable which is more important than finite accuracy.
Sorry to bore you with this but it seems to need putting straight.
Regards Alan
Note that the 40bhp refered to relates to transmited losses for a 4WD vehicle.
Originally Posted by Alan AVA
Hi
Thanks to all who came to the rolling road day,interesting chatting to you & seeing your cars & the various modifications,
generaly very impressive results from most tested.
I read the comments on flywheel estimates with interest.
To clarify our position
At the roller speed at which we are testing these cars the losses would be approx 40bhp.
To justify this consider the theory of the 24% loss.
A car tested produces 200bhp at the wheels,add a 24% to this &
we get an estimated flywheel figure of 248BHP.
The car is then modified & produces 400bhp at the wheels at the same roller speed & engine speed.We then add the 24% to this &
a figure of 496bhp is arrived at.
This means that as the BHP rises so does the loss figure.
As the rpm has remained the same this means that the loss is
also measured as a loss of torque.
That means that as the torque rises so do the losses.
However if it is accepted that a rise in torque would increase the
the actual loss then it must also be the case that an increase in the measured at the wheels torque would also result in an increase in the losses.
ie if you test in third gear you might get say 1000lbf of torque
in fourth you might expect 800lbf of torque
in fifth you might expect 600lbf of torque
whereas you might expect 1200lbf of torque in second
That would mean that the losses in second with a 24% loss applied will be higher than in fifth with 24% applied.
In fact what happens in real tests is that the power figures DROP in each higher gear,the opposite of the % theory.
Also if these losses exist then where is the power going?
It would have to be heat or noise,I can't say I have ever noticed any rise in transmission noise or had it reported to me.
Heat ? Using our earlier theoretical model with a 96BHP loss
that would mean approx the heat of 70 1 bar electric fires in your
transmission & tyres.
Also if this loss is an under power loss then the inertia test which uses run down times(rate of slowing down of the rolling road)
to work out a flywheel figure could not work as clearly both of our theoretical cars must have the same run down time.
Why?
Confusion I believe arises from the terminoligy used,
ie the losses called "transmission loss" would be better named as "transmited loss" which does not infer that the loss is in the transmission.
"Transmited loss" is made up of a number of factors largest of which is the power required to drive the rolling road & rises
in a non linear fashion with the roller speed.
ie higher speed(gear) higher loss at the wheels.
The % alluded to is in there as well but is probably very small
(1 to 3%)as a guess.
This theory unlike the % theory covers most of the anomilies that arise during testing.
It also explains why BHP at the wheels seems to vary from rolling road to rolling road as different gears used or different roller diameters give different hard to figure results.
To qualify this opinion I offer 24 years of rolling road operating,
testing over twenty thousand cars of all makes.
The 40BHP mentioned is an approximate loss is based on the power consumption of two sets of 20" rollers at the speed of testing approx 80mph.
Also to those who question the test method,as this is how you measure BHP not HP & being the method of succesfully testing of the twenty thousand cars mentioned I don't see the problem.
Inertia testing as you mentioned is faster however does not allow for stabilising of readings,boost,temp,gas annalysis etc
& does not IN MY OPINION offer you the consumer the best deal.
It has only become the "norm" with the fast computers & in recent years.We can do inertia testing but in most instances choose not to.
Loaded testing simulates the worst case scenario for the car ie 170mph,4 heavy mates,up a hill,into the wind.& therfore predicts the outcome that as a tuner you are responsible for,of whether the car will survive that encounter,tuning to less stringent criterea may appear to give better results but only in the the short term or for those who don't subject their car to all it is capable of.
It is also very repeatable which is more important than finite accuracy.
Sorry to bore you with this but it seems to need putting straight.
Regards Alan
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