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This is not a
"user" feature however and is only for internal use by
myself. The same feature can also measure the losses
that a car / bike transmission & tyres cause. It does
this the same way, in that after a run the vehicles clutch
is disengaged, and then the drum is logged as it slows back
down to a standstill. This allows us to create a
"negative" BHP curve showing the road speed v the
transmission and tyre losses. This curves data can be
inverted and added to the measured power curve to give a
"flywheel or engine power curve!
It can never be
truly accurate though because there are actually MORE losses
than this under load because one component of the losses
depends on the actual torque being transferred. Gear teeth
under high load "slide" against each other giving increased
friction (although only minor due to the oil film) and the
same applies to thrust bearings etc inside gearboxes and
diffs. This method cannot know how much this happens as it
measures the power required to turn tyres, gears, chains,
etc whilst not under load conditions.
So SOME software
adds a percentage! as well... Which is simply wrong! It is a
kind of "fudge factor" that hopefully arrives at a figure
that is approximately correct! Sometimes this
fudge factor is increased and decreased according to the
torque / speed etc.
Some (really dodgy
dyno systems) just "guess" at a percentage!!! (You
know who you are!) which is so far from being correct its
simply criminal!
Remember that it
is NEVER a percentage.
With an average
transmission, (gearbox/differential, tyre roller interface)
you are looking at roughly the following variables:
a) Tyre /
roller interface - for any particular tyre / drum the
following is true... To begin with there is quite a
high value from 0 to say 1 mph. This stays as speed
increases but the power needed slowly increases with the
road speed, (not engine RPM!). So this loss is greater
in taller gears and at higher speeds. Again it almost
completely unrelated to the unrelated to the power being
applied. So is not a percentage of power! UNLESS
they spin...
b) Rear (or
front) diff / axle (car) losses - This is
both load (torque) related as well as Road speed related.
Both components need to be considered here. Oil drag,
and grease in CV joints and wheel bearings and prop shafts,
as well as internal windage losses and external windage
losses on prop shafts etc, all increase as road speed rises.
They are NOT engine RPM related or Power related. These all
increase with road speed only, and are independent of the
gear the vehicle is in. These are the largest cause of
the total losses in differential, prop shaft, drive shaft,
or wheel bearings.
However some other
losses also occur in diffs and axles that are load
(torque) related... Gear teeth, side loads caused by
helical cut gears on thrust bearings etc do experience
greater losses as the torque going through them increases.
This effect is pretty minor compared to the above, but does
occur. There is obviously an oil film present, or the
components would destroy themselves, but the increase is
measurable.
Every car is
different so its impossible to say how much is determined by
speed and how much by load... And of course the gear
you are testing in matters too! In top, there would be
far less torque, but far more speed! So you get more of one
type of loss and less of the other! But since the
majority of the losses are the first type you will get more
power in third than in top gear actually reaching the
rollers.**
** Theoretically,
but since 4th gear is 1 to 1 ratio, or "straight through" in
most cars there is less gearbox losses in 4th!
So in this case you will now read best power at the wheels
in 4th gear!
c)
Gearboxes - losses in gearboxes are similar to those in
an axle or a differential. Most of the losses are
simply, bearing, and oil drag. These are engine RPM
dependant, not power or torque dependant. Some of the
losses ARE dependent on the power and increase as the power
transmitted goes up. Marginally. So again a simple
percentage cannot be used, and measuring the losses by
letting the dynamometer "push" the vehicle with the clutch
disengaged also does not allow for these load dependent
values either...
So NO "engine
figures" can be accurate! Only go by the real recorded
"at the wheel", corrected figures!
This is not a
"user" feature however and is only for internal use by
myself. The same feature can also measure the losses
that a car / bike transmission & tyres cause. It does
this the same way, in that after a run the vehicles clutch
is disengaged, and then the drum is logged as it slows back
down to a standstill. This allows us to create a
"negative" BHP curve showing the road speed v the
transmission and tyre losses. This curves data can be
inverted and added to the measured power curve to give a
"flywheel or engine power curve!
It can never be
truly accurate though because there are actually MORE losses
than this under load because one component of the losses
depends on the actual torque being transferred. Gear teeth
under high load "slide" against each other giving increased
friction (although only minor due to the oil film) and the
same applies to thrust bearings etc inside gearboxes and
diffs. This method cannot know how much this happens as it
measures the power required to turn tyres, gears, chains,
etc whilst not under load conditions.
So SOME software
adds a percentage! as well... Which is simply wrong! It is a
kind of "fudge factor" that hopefully arrives at a figure
that is approximately correct! Sometimes this
fudge factor is increased and decreased according to the
torque / speed etc.
Some (really dodgy
dyno systems) just "guess" at a percentage!!! (You
know who you are!) which is so far from being correct its
simply criminal!
Remember that it
is NEVER a percentage.
With an average
transmission, (gearbox/differential, tyre roller interface)
you are looking at roughly the following variables:
a) Tyre /
roller interface - for any particular tyre / drum the
following is true... To begin with there is quite a
high value from 0 to say 1 mph. This stays as speed
increases but the power needed slowly increases with the
road speed, (not engine RPM!). So this loss is greater
in taller gears and at higher speeds. Again it almost
completely unrelated to the unrelated to the power being
applied. So is not a percentage of power! UNLESS
they spin...
b) Rear (or
front) diff / axle (car) losses - This is
both load (torque) related as well as Road speed related.
Both components need to be considered here. Oil drag,
and grease in CV joints and wheel bearings and prop shafts,
as well as internal windage losses and external windage
losses on prop shafts etc, all increase as road speed rises.
They are NOT engine RPM related or Power related. These all
increase with road speed only, and are independent of the
gear the vehicle is in. These are the largest cause of
the total losses in differential, prop shaft, drive shaft,
or wheel bearings.
However some other
losses also occur in diffs and axles that are load
(torque) related... Gear teeth, side loads caused by
helical cut gears on thrust bearings etc do experience
greater losses as the torque going through them increases.
This effect is pretty minor compared to the above, but does
occur. There is obviously an oil film present, or the
components would destroy themselves, but the increase is
measurable.
Every car is
different so its impossible to say how much is determined by
speed and how much by load... And of course the gear
you are testing in matters too! In top, there would be
far less torque, but far more speed! So you get more of one
type of loss and less of the other! But since the
majority of the losses are the first type you will get more
power in third than in top gear actually reaching the
rollers.**
** Theoretically,
but since 4th gear is 1 to 1 ratio, or "straight through" in
most cars there is less gearbox losses in 4th!
So in this case you will now read best power at the wheels
in 4th gear!
c)
Gearboxes - losses in gearboxes are similar to those in
an axle or a differential. Most of the losses are
simply, bearing, and oil drag. These are engine RPM
dependant, not power or torque dependant. Some of the
losses ARE dependent on the power and increase as the power
transmitted goes up. Marginally. So again a simple
percentage cannot be used, and measuring the losses by
letting the dynamometer "push" the vehicle with the clutch
disengaged also does not allow for these load dependent
values either...
So NO "engine figures" can ever be accurate if measured on a
chassis dynamometer!
Only go by the real recorded "at the wheel", corrected
figures!
Below is a copy of
an email that I just replied to...
Basically its NOT
ever a percentage! Or close to one and it never can
be.
Because if I were to take for e.g. 2 stock old GSXR Suzuki
race rep 750 bikes, both would give me say 100rear wheel HP
in 3rd 4th and maybe 2 less in 5th and 6th.
The two less are simply aerodynamic losses on the wheel and
tyre due to the 170mph wheel speeds...
Now, add 50bhp of nitrous to the 2nd bike.
Dyno it and it makes almost 50 BHP extra! There are NO EXTRA
losses other than one or two hp, in thrust bearings and gear
faces etc.
Now, add another 2nd 50 BHP of nitrous to the 2nd bike in
the form of another stage - now it makes 100 BHP more.
If it were a percentage then the second kit would show a
smaller power increase! But it doesn't of course.
I have done this sort of thing so many times and always with
the same result.
Once the motor has overcome the frictional losses that are
simply speed related, nothing else seems to change much.
Now the manufacturer claimed 112 BHP at the motor, so
100bhp represents 12hp losses. Or about 12 "percent" if you
prefer!
But the second bike with the extra power has only 5 or 6
percent losses now! if you were expressing it as
a percentage!
Now take the "touring" version of the same bike engine with
its smaller carbs, low compression, smaller valves, softer
cams etc.
Manufacturers engine claims are now 70bhp. But on the dyno
we see only 58 or so...
So its losing almost the same 12bhp.. But now its a
whopping 17.4 percent transmission losses! But its the
SAME transmission...
So if it really WAS a percentage fitting the same nitrous
systems to this bike would give LESS power!
But guess what! 100 extra total would be seen again... No
17.xx percent loss....
Which of course is correct because it uses the same
transmission and wheel and tyre..
If you measure the power required to "push" the
transmission/wheel as far as the clutch at the same road
speeds in the same gear it will say the same thing (12bhp).
The losses on both bikes will be identical 12hp (at max -
speed not power dependant) required to overcome the rolling
resistance of the parts, tyre, chain, oil etc.
This loss isn't a constant but increases and changes with
speed and gear ratio.
There is also a small element of this that increases with
torque, but at least on bikes transmissions this is pretty
small...
Hope your head doesn't explode!
Burgerman
Another reply!!!
To:
burgerman@ntlworld.com
Sent: Saturday, May 22, 2004 10:02 PM
Subject: Re: email from the Dyno Information pages
Thanks for the reply. I am talking car. 267bhp measured at
the wheels. Roller guy reckoned 30% loss on fly wheel BHP
any thoughts
Cheers Chris
One third of your power (approx) is 89bhp!
If you REALLY lost 89 BHP as "waste" power it would show up
as heat!
Into the oil and castings...
To convert this to watts multiply by 760...
Result = 67540 watts apparently went as heat!!! That
would run a small town...
Your transmission would have melted, the oil boiled away in
a massive cloud very quickly...
Burgerman.
www.optimabattery.co.uk
www.burgerman.info
www.fatnfast.com/robot
www.nitrous.info
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