Drivetrain loss.. How much do you really lose?

[river]

Hi,

Good point!

I assume there is a minimal and constant drain of power required to move the drivetrain. The faster you move the drive train the more drag (for want of a better word) you will encounter. As mentioned, the faster the drivetrain goes, the more power will be required to keep it moving.

I just don't get that doubling the power of the engine will also double the losses in the drivetrain. But, then again, I may be wrong. I would think the losses would move up a bit as the power of the engine increases, but I am not sure it would be the same amount of loss, as a percentage, of the lower powered engine.

This is got me horribly confused. I now feel the need to check this out and investigate further.

seeyuzz
river

[myne]

Well, I guess it's possible that they're only counting losses under maximum acceleration, in which case, the % might hold true.
Afterall, in drag racing it takes something like 2x the power to do a 9sec pass instead of a 10sec pass. So obviously it's less efficient to accelerate quickly. A 400kw engine would easily out accelerate a 200kw engine so perhaps by virtue of the fact that the components are being forced to accelerate faster, they require more energy to overcome their rotational inertia.

[MWP]

It would be nice to know the real figures of drivetrain losses... but really, does it matter?

When it comes to performance of a car, wheel power is all that really matters.
So why bother trying to work out engine power... is it just so you can tell people a larger HP figure to make the car sound more impressive?

[river]

Hi,

Found this.... http://www.superstang.com/horsepower.htm

seeyuzz
river

[Nim]

I've allways pondered this. I've come to the conclusion that there is X amount of power needed to spin the gearbox and drivetrain, and then there are some extra losses as the various parts heat up more from the extra force, rather than just moving with more power. I'd assume it's mostly 'drivetrain needs X power to spin it at X speed'.

I'll ask that phisics dude next time I see him (hopefully tomorrow).

If you make more power by raising the redline and point of power delivery, then yeah, your losses are going to go up as a direct percentage (the drivetrain is spinning 20% faster so needs 20% more energy to keep it spinning). However, if you just apply more boost, or increase your displacement, your power loss through the drivetrain should stay relativly the same.

However, these are just my musings, and might be way off.

[love ke70]

in the case of things spinning faster taking more power etc, we could test that by doing a dyno run in 2nd 3rd and fourth and see what the result wont be
it wont tell you the loss in your drivetrain, but it will determine whether spinning the drivetrain faster does take more power...

[off-road]

Those of you with aftermarket programable ecu's that are able to log injector duty cycles
can calculate horsepower at flywheel based on injector size.If this is done while tuning on chasis dyno it should be easy to calculate driveline loss.

[brett_celicacoupe]

i say there is no way of accurately guaging the difference. to many variables! some people just say 1flykW = 1rwhp

remeber that to measure kw/nm they have to load the engine up, but remeber that loading it up will create more than normal friction in drivetrain components.

i guess the only truely accurate way to measure power/torque is to stop 'time' and place a device on the wheel/flywheel to measure force at a point on the wheel/wheel.


also consider the energy required to get the driveline mass rotating, and then stored energy that is released when the system is decelerating......

it all a bit foggy

[brett_celicacoupe]

in the case of things spinning faster taking more power etc, we could test that by doing a dyno run in 2nd 3rd and fourth and see what the result wont be
it wont tell you the loss in your drivetrain, but it will determine whether spinning the drivetrain faster does take more power...

in lower gears the car would produce more torque at the wheels. i dont think it would work

[30psi 4agte]

Those of you with aftermarket programable ecu's that are able to log injector duty cycles
can calculate horsepower at flywheel based on injector size.If this is done while tuning on chasis dyno it should be easy to calculate driveline loss.

Thats abit hard as fuel pressure varies between set ups. I was running 550cc injectors at 55 psi and they were MAXED out and it made 283 rwkw (379.5 hp ).

They say that the 550 are SUPPOSEDLY good for 500 hp @ fly on stock ( 36 psi ) fuel pressure .
so this therory wont work.

I have herd double your rwkw and change to fly hp I.e 250 rwkw = 500 hp @ fly
But even this is abit out.

I have also herd that you loose 1/3 engine hp through drive train.

I think there is a limit to how much you loose and in a 4a with sprinter box id say 80 hp max

[SL666]

in the case of things spinning faster taking more power etc, we could test that by doing a dyno run in 2nd 3rd and fourth and see what the result wont be

pretty sure that makes a difference.. so the rule of thumb is to run the gearbox in as close to 1:1 as possible..

[kemicalx]

pretty sure that makes a difference.. so the rule of thumb is to run the gearbox in as close to 1:1 as possible..

Hmm i thought that only effected the torque reading?

[30psi 4agte]

yeah it does make a diff but most dyno these days are very good and can account for this through wheel speed etc.

[TA-022]

just for shits and gigles i use 15-20% FWD and 30%RWD (4wd r teh suk)

this is purely speculation and only for the purpose of arguing with mates. this loss I put down to being that of parasitic loss with spinning shafts etc.

rwd has more loss of course because of added diff and tail shaft where as fwd exits box to wheels.. yada yada.

30% loss with 100 fly kw = 70rwkw
30% loss with 300 fly kw = 210rwkw

of course if you make more fly your loss is greater .. but stil that constant of 30%.

just my opinion and like mentioned all guess work based on individual speculation unless you bring proper hardcore physics and crap into play. And then you'll spend so much time working stuff out you'll never get a chance to drive ya 300rwkw.

[BrianRA23]

How much power do I really want to loose?

In my Celica if I am planning to have around the 200rwkw then an F series diff makes sense since appparently it can handle the power. Although I have a RN2x hilux I was going to fit.

The G is obviously stronger and arguments are typically about unsprung weight being a reason to go with the F. But being bigger it may take an extra 5% power to spin it.

For 200rwkw, if 5% is right then this could equate to an extra 10 to 15kw getting through.

It would be interesting to know the power loss for a range of gearboxes and diffs as the results might show that a particular series is very efficient - the smaller ones might not be more efficient due to the angle of gears, bearing type / size and noise suppresion etc.

Does anyone know if when a gearbox/diff is reconditioned is their a list of specs for how much it takes to spin it on final inspection before it is deemed OK?

Once I get an F series diff I might try to remove the brakes on each and see how fast my cordless drill can spin it compared to the G series - it may still end up going in.