On a street car with typical OEM manual and auto is it generally the 15% and 18% respectively?

Does 500rear wheel hp mean nearly 600 engine hp?

Is there a scale?

 

No the scale remains the same but that supposed set scale seem a to vary from what I've seen

 

It is a good question. I always had a X amount of HP theory but that got debunked. It does highlight the value of driveline efficiency as HP increases.

 

An acquaintance with a BBC made 709.9hp at 5800rpm on an engine dyno and so thought to ask how much that will be rear thru a TH400

 

As hp increase parasitic loss increases as well yes

 

He isnt asking that. He is asking does percentage change. Not does the amount change.

 

It makes sense to me that the losses would increase as power increases, just for the simple fact that as you make more power your driveline needs to be stronger and therefore heavier. You wouldn't expect the 4l60e and 7.5" rear end from a 90's camaro to survive behind a bored, stroked, and blown LS, so you throw in a 4l80e and a dana 9 inch rear to take the power. Heavier components equals greater driveline losses.

 

it isn't a linear scale.

some things take a fixed amount of power to drive, like the water pump. some vary by the load placed on them, like the alternator or power steering. some do absorb more power as input power rises, like a transmission or differential, for various reasons, like internal friction, heat, pumping losses, etc, and again, this is not necessarily linear. things like flywheels, driveshafts, and axles take rotational energy to move, and the amount will depend on the inertia of momentum of the rotating part and the rate of rotational acceleration. even the engine itself has internal losses.

so, it's not a simple answer. the percentage is an easier way to guess at it, as is some people stating "this trans or driveline absorbs x amount of power."

 

Also takes more and more power just to accelerate the mass more quicker.

 

Basically I think the consensus is that you'll never know the exact loss on any particular setup until you you get it on the dyno and see what it makes at the wheel

 

not sure what you mean by that, but that is ultimately true.

newtons equation is pretty linear. F=ma. angular acceleration takes a similar form. power is pretty linear, too. power = force x (distance/time).

but, that doesn't really relate to power/weight and quarter mile time, the reason being (i would imagine) that the total forces on the car aren't constant during a run. force to the wheels changes during a run due to gearing, torque curve, parasitic loss (which can increase with speed and rpm as well as horsepower, depending on the component contributing to the loss), and acting against the car as well you have areodynamic drag, rolling resistance of the tires, etc.

looking at graphs of mph and ET's vs power/weight from data sets taken from a lot of different cars, you never see a line. it's always a curve that falls off the faster the cars go.

 

Basically what meant was you will consume more tq to increase angular acceleration of the same mass. Speaking specifically of driveline here. And including the rear wheels. Since hp is ultimate tq dependent, you consume more power to accelerate driveline rotation faster.

Probably said the same thing you just said.