Power loss - relative or absolute

[denisb]

Is power loss relative (a percentage of total power) or absolute (x BHP, irrespective of power)?

The best example I can think is the loss caused by piston ring friction. Surely this is a function of the rpm, stroke, bore, number and thickness of the rings rather than the power being made at any one rpm?

Another example which contradicts this is transmission gears. As the friction will increase with loading (torque) then it is presumably a function of torque, if not BHP.

Any ideas?

[GreenV8S]

I guess it's some of each as you suggested.

[deeen]

I think these things are never that simple - the friction in the cylinder will increase with torque because the sideways loading on the piston increases, and the losses in the gearbox will vary with gear (direct / indirect) and temprature. For example. I think.

[chuntington101]

there are soooo many factors that it is hard to say this or that.

but poer loss is normaly said as a percentage be it in industry or on a car.

thanks Chris

[350matt]

Typically the friction curve tends to increase at an expondential? rate with rpm so friction may be 10% at 2000Rpm but 40% at 18,000Rpm

Matt