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Why Bhp(kw)
- Thread starter joebgd
- Start date
Oldschool
XS650 Member
BHP (Braking) is a measure of horsepower at the wheels. HP is the horsepower totally available at the engine. Braking would be expected to be less. In farm country where I live, we often express it as (hitch) horsepower as it's important to understand the size of of the implements that we can pull.
Think of it this way. HP is what your paycheck starts out at. BHP is what you get to cash it for.
Brake hp is whatever is available at the rear wheel, propeller shaft, pto shaft. So is actual, useful power output, often measured with an electrical or water brake.
At "the other end" is Indicated hp. Which basically is average cylinder pressure times engine capacity times rpm (corrected for 2 or 4 stroke engine) Or put differently, power at piston, before all frictional and transmission losses. On large marine diesel engines, indicated hp is checked on a regular basis, via pressure sensors connected to the combustion Chambers.
At "the other end" is Indicated hp. Which basically is average cylinder pressure times engine capacity times rpm (corrected for 2 or 4 stroke engine) Or put differently, power at piston, before all frictional and transmission losses. On large marine diesel engines, indicated hp is checked on a regular basis, via pressure sensors connected to the combustion Chambers.
mike in idaho
XS650 Addict
A kilowatt equals 1.34102 horsepower, a metric measure of power.
I had drummed into me at trade school. 1 HP = 746 W and another one I remember is "Watts a Joule per second".
Or 1 W= 1 Nm/s.
( Not torque as in Newtonmeter, rather force times distance divided by time, in linear movement. Or force times speed)
It is actually the SI unit for power. (SI=International Standard unit)
Imperial units are by no means "standard", except in the US
Last edited:
Max Midnight
XS650 Addict
Horse power was first used by James Watt to define the equivalent work a steam engine could do compared to a horse. Watt defined 1 horsepower as 'the amount of work required from a horse to pull a 150lb weight up a shaft that was 220 feet deep'.
Later, John Smeaton estimated that a horse could produce 22,916-foot-pounds per minute, and John Desaguliers increased that to 27,500-foot-pounds per minute.
Foot-pounds is used to describe torque i.e. twisting power. As work performed by a force is the product of force and displacement of the body, 33,000 foot-pounds represented the work performed by the horse.
Indicated horse power, usually abbreviated to HP is determined by the pressure in the cylinder(s) and will be greater than BHP as it excludes friction and other losses.
A more useful measure of how much work an engine can produce is when the losses due to friction etc. are removed.
The term 'brake' in Brake Horse Power (BHP) describes how a turning shaft from the engine has a brake applied to it and the torque exerted on the brake and is measured on a dynomometer. The measurement can be taken at the flywheel or at the driven wheel(s).
BHP = torque x r.p.m.
So, the HP of an engine is the theoretical maximum power excluding the losses described above and BHP is the actual power it produces.
As per the conventions, 1 BHP is equal to:
Later, John Smeaton estimated that a horse could produce 22,916-foot-pounds per minute, and John Desaguliers increased that to 27,500-foot-pounds per minute.
Foot-pounds is used to describe torque i.e. twisting power. As work performed by a force is the product of force and displacement of the body, 33,000 foot-pounds represented the work performed by the horse.
Indicated horse power, usually abbreviated to HP is determined by the pressure in the cylinder(s) and will be greater than BHP as it excludes friction and other losses.
A more useful measure of how much work an engine can produce is when the losses due to friction etc. are removed.
The term 'brake' in Brake Horse Power (BHP) describes how a turning shaft from the engine has a brake applied to it and the torque exerted on the brake and is measured on a dynomometer. The measurement can be taken at the flywheel or at the driven wheel(s).
BHP = torque x r.p.m.
So, the HP of an engine is the theoretical maximum power excluding the losses described above and BHP is the actual power it produces.
As per the conventions, 1 BHP is equal to:
- 745.5 watts
- 1.01389 ps
- 33,000 ft lbf/min
- 42.2 BTU/min
