Drivetrain losses (ad nauseam...)

[Vtecoupe]

All such a good read.

Anyone have the post that Mario ( GTR-700 ) did on the WRX Yahoo Groups a couple years back ?

From memory, he engine dynoes his WRX motor and then put it in the car and put it on the rollers. He lost about 60kw through the drivetrain before and after he modified the WRX motor ( 160kw standard and 300kw+ after )

[DoctorEvil]

Yep-tyre to roller interface is the culprit.

Even a 1st year engineer should be able to see that claiming %losses through a manual gearbox is ridiculous.

I can just imagine the meeting where a team of engineers submits a new drivetrain design proposal to management that has a power transmission efficiency of 70%...............

The problem isnt as simple as this, the gearbox efficiency is more likely to be around 95-98% efficient. The diff probably also has an efficiency rating of 95-98% as well. The CV joints and prop shaft probably also have the same efficiency rating.

Combine all these losses together, then add the percentage loss of the tyre-dyno interface, and there you have your 15-20% 'drivetrain' loss that you see when you get a reading on the dyno.

If anyone thinks that this value is a static figure then you are a brain dead dickhead basically.

Enjoy..

[Process West]

All such a good read.

Anyone have the post that Mario ( GTR-700 ) did on the WRX Yahoo Groups a couple years back ?

From memory, he engine dynoes his WRX motor and then put it in the car and put it on the rollers. He lost about 60kw through the drivetrain before and after he modified the WRX motor ( 160kw standard and 300kw+ after )

I remember Marios emails ....I think he had that WRX engine on the engine dyno and then back in the car on 4 different occasions (power levels)....the 60kw loss was consistant whether it was 200kw atw or 350kw atw....

Drive train loss is definately not a percentage...

Kevin

[BigMuz]

Good one P west, you're a freaking genius.

What if we open the throttle enough to make 60 kw- what does the dyno read now? 0? O K....

Ummm you can't lose power through a "theoretical gear ratio interface secoh . The whole torque x Speed = Power bit

That is true within similar ratios, but a 5 tooth to 50 tooth gear makes a lot more heat (and is therefore less efficient) than a 20 to 20 gear ratio.

(Just trying to undig old mate Secoh...:D)

Muz

[The Pupat]

That is true within similar ratios, but a 5 tooth to 50 tooth gear makes a lot more heat (and is therefore less efficient) than a 20 to 20 gear ratio.

(Just trying to undig old mate Secoh...:D)

Muz

There's always one. :p



Engine loss can not be a static value end of story. Anyway that thinks it is is a farkin moron and needs to learn how gearboxes and and more importantly gears work.

[Belly_up]

just thought i'd add this little gem of a quote from a recent Autospeed article, thought it might be relevant, in an incorrect-and-irrelevant kinda way

With the shortened final drive ratio (which is said to reduce measured power), JP’s GTi has recently blasted out an amazing....blah blah blah

(my emphasis added)

[Process West]

Quote"What if we open the throttle enough to make 60 kw- what does the dyno read now? 0? O K...."

Fair comment above....but why did Mario always have a 60kw drive train loss no matter what the engine power was?

Kevin

[BigMuz]

just thought i'd add this little gem of a quote from a recent Autospeed article, thought it might be relevant, in an incorrect-and-irrelevant kinda way


(my emphasis added)

If you go from a 2.5 to a 4.5, I bet the rear wheel power drops- logical that having a tailshaft and pinion turning really fast must take more power away from the wheels. Whether that makes up for the lower energy to turn the rear wheels slower...

Muz

[ccpl]

Ok my understanding of this is...

If i give less than 10% of a shit about this post, and ive used up 47kw of energy reading the gibberish posts that make up this thread. What is the approxiamate coefficient of drivetrain loss comparative to my absolute and utter disregard for this thread? I believe that it is a constant of 100% of "GET A LIFE PEOPLE"

my $1.56c

[Spac]

Some good comments and some utter shit - as always happens when this topic comes up.

1. A mate ran his Celica on the dyno in every gear. Spat out the exact same power figure every time. Obviously the tractive effort figure went up and down like crazy depending on what gear he was in, but the measured rear wheel power remained identical.
Therefore there is no difference in the available POWER at the rear wheels depending on the gearing.
HOWEVER, and anyone who's fitted 5.1s to anything RWD can tell you, they make more noise than 'normal' ratios like 3.9 (or taller). Noise = energy = power loss. There would "have" to be additional heat produced too, so the difference will be more than the insignificant energy in the audible noise.
So there must be some additional "drivetrain loss" from a shorter ratio diff - how much it is open to debate, but it is definitely a product of less effiecent gear design and definitely not a product of the different speed of the wheels (compared to the alternative ratio).

2. Ever driven a car with a crook gearbox or diff bearing? The noise (and therefore the waste energy) goes up with speed and with load, doesn't it!
This alone should be enough for even the least technically minded person to see that drivetrain losses are NOT a constant.

The losses through a car's driveline will NOT be constant across all rev/load/power levels, so it is ridiculous to suggest that the losses will be a fixed amount.
However, it is also nearly as ridiculous to suggest that a blanket 25% figure is going to be totally accurate... Say you measure and prove that you have 25% loss in a certain condition (say, half throttle, nearly full revs and whatever load the dyno is applying to hold the revs static). Now say that you lifted off the throttle and reduced the dyno load - I'll bet that your drivetrain losses have just dropped down to less than 25%... Similarly, if you stood on the go pedal without reducing the dyno load, the drive train losses will go up compared to the steady state situation.

[DoctorEvil]

Ok my understanding of this is...

If i give less than 10% of a shit about this post, and ive used up 47kw of energy reading the gibberish posts that make up this thread. What is the approxiamate coefficient of drivetrain loss comparative to my absolute and utter disregard for this thread? I believe that it is a constant of 100% of "GET A LIFE PEOPLE"

my $1.56c

If you cant add anything constructive to this thread then dont post anything..

[ccpl]

If you cant add anything constructive to this thread then dont post anything..

By posting that, you have breached your own rules.

Now how bout you mind your own business, and take it like the joke that it was!