BHP

[kenny]

How is BHP measured, I can understand how it's measured at the wheels on a rolling road but how is it measured at the flywheel, is it some sort of calculation?

[stan]

if your taking a power reading from a rolling road, this is a calculated figure using braking force required (torque) for a given engine speed.

this is measured wheel power. to get this to flywheel power, its either calculated as a percentage, say 17% losses, or the machine can do a run down test to measure losses. this method isnt accurate however due to the inherent difference in losses between when gears are loaded and unloaded.

an engine dyno is the only accurate way to obtain flywheel power figures.

[kenny]

When you talk of braking forces do you mean the roadbrakes or enging braking, ie taking your foot off the loud pedal. If it's roadbrakes will poor performing brakes enhance the measured bhp?

[MAXIBOY]

no the braking is applied by the rolling road against the tyres.

[kenny]

I guess the true measure of engine power is at the flywheel then, but a cars absolute power is at the wheels. Williams are quoted as 150, is that wheel or flywheel?

[MAXIBOY]

at the flywheel. a cars true usefulness is measured at the wheels in a combination of power torque and having large amounts across a wide range rather than a very peaky power torque graph

[kenny]

Thanks maxiboy, picking up car tomorrow that has +24bhp, didn't think to ask where it was measured but it's deff 24 up on original if at the flywheel. If it's at road then it's a lot lot higher :) . The guy did say who done the remapping etc but can't remember what he said so will have to wait to get paperwork

[stan]

I guess the true measure of engine power is at the flywheel then, but a cars absolute power is at the wheels. Williams are quoted as 150, is that wheel or flywheel?

wheel power and engine power are only different due to the losses incurred by the transmission.
Discrepency with obtaining EITHER figure from a rolling road comes from the ammount of variation experienced through using a tyre basically.

An engines performance is directly related to what you see at the wheels anyway...torque is multiplied by the gearbox, so its a combination of alot of factors....but yes as maxiboy says you want the engine to be making useable torque and power.