Why do we refer to BPH nowadays instead of simply HP?

As a kid, we always just talked about cars or motorboats having a certain amount of horsepower. Now, it’s always ‘brake horsepower’.

Come to think of it, mind, I am not sure I have ever heard bph used in reference to outboard motors…

Historical reasons, I think. Horsepower was calculated using a formula for steam engines – rather than measured directly. I think involving piston surface area etc. It isn’t really an accurate measure of power but meant to give an indication of number of horses an engine should be able to replace.

Brake Horsepower was introduced as a better measure and is a measured power (using a brake, I guess) – and is equivalent to about 746W. For any modern engine, I think you can interpret HP as BHP pretty safely.

Disclaimer – this is from vague memory and I can’t access Wikipedia just now.

Brake horsepower is apaprently the engine’s horsepower, before it gets transmitted through the gearbox, wheels and whatnot, which all incur losses. Horsepower is just a shorthand afaik.

I suppose that with boats there’s far less gearing to go through, so the two are probably closer and more closely linked.

Apparently though the original definition of horsepower was based on a flawed calculation and 1hp does not relate to a typical horse at all.

People will often use PS now, rather than (B)HP, cos the numbers are fractionally higher. 180PS sounds more than 177BHP.
Car companies on mainland EU tend to use kW though, which kinda makes sense.

What Euain said basically – BHP is the peak power of the engine measured by the water (or magnetic etc) brake when it is dyno tested, rather than the power that ends up at the wheens or the theorical/historical number of horses that the machine could replace.

There seems to have been a bit of move to quote power in PS or Pferdestärke (horse-strength in German), or kW, (presumably to standardise with base SI units)….. those pesky Europeans 😉

EDIT: Damn my slow fingers….

If PS if German for “Horsepower”, why are the numbers different? Do we have bigger horses?

I picked up a bad habit of saying “bhp at the rear wheel” which means “horsepower without drivetrain losses, with drivetrain losses”.

Only cos the UK found out how much power a horse had, then rounded it up. The Metric Horsepower (PS) is pretty much the same as the number they had found before rounding.

The UK motor industry rounded up horses?

Bunch of cowboys.

Or the British brewery horses were on anabolic steroids.

Northwind – Member

I picked up a bad habit of saying “bhp at the rear wheel” which means “horsepower without drivetrain losses, with drivetrain losses”.
What happens if its front wheel drive? 0bhp? 😆

Historical reasons, I think. Horsepower was calculated using a formula for steam engines – rather than measured directly. I think involving piston surface area etc. It isn’t really an accurate measure of power but meant to give an indication of number of horses an engine should be able to replace.

Brake Horsepower was introduced as a better measure and is a measured power (using a brake, I guess) – and is equivalent to about 746W. For any modern engine, I think you can interpret HP as BHP pretty safely.

This.

HP is a mathematical thing, calculated from the efficiency of the engine, calorific value of the fuel, friction etc.

Brake horse power is measured output of an engine dynamometer (dyno, engine ‘brake’).

I picked up a bad habit of saying “bhp at the rear wheel” which means “horsepower without drivetrain losses, with drivetrain losses”.

No it doesn’t. It means HP measure on a chassis dynamometer (brake). Nothing wrong with that at all. Just be sure to call it RWBHP (rear wheel BHP) or FRBHP (front wheel BHP).

Come to think of it, mind, I am not sure I have ever heard bph used in reference to outboard motors…[/]

BHP is the number of horses pulling the other direction to stop you moving.

It is not used on boats as the horses might drown while testing it.

BHP is the number of horses pulling the other direction to stop you moving.

It is not used on boats as the horses might drown while testing it.
The horses pull a lot less well when they are swimming anyway.
The really bizarre thing of course is that the actual peak output of a good horse has been measured at close to 15hp. 1hp is what an average working horse in Stevenson’s time could produce all day.

Cougar – Moderator

The UK motor industry rounded up horses?

Bunch of cowboys.

Kwality 😆

The really bizarre thing of course is that the actual peak output of a good horse has been measured at close to 15hp. 1hp is what an average working horse in Stevenson’s time could produce all day

True, but that was the beauty of heat engines, in that (provided you could fuel it and it was reliable) you could run it at peak power all day. The horse gets tired, bless. The fuel thing was the issue with early steam engines – <1% thermal efficiency takes a lot of coal to produce anything meaningful.

peak output and sustained output are different things.
even a human can have a peak output exceeding 1HP, but a horse towing beer kegs, or pulling a millstone round, or towing a plough or whatever, can sustain that 1HP all day. I guess the 15HP is a thoroughbred in a sprint flat race?

Now let’s really get the confusion going by talking about torque. Or torquing about talk.

I guess the 15HP is a thoroughbred in a sprint flat race?

I’d guess so, Not too surprising really, you’d do well to make a vehicle weighing 1/2 ton that could hit 40mph on a soft grass surface with power output of 1bhp.

Torque is less confusing imho. Especially where rotational motors are concerned.

Torque is more confusing imo. It’s torque that makes you go, not power.

Each bang in the engine produces a set amount of force. More force = more torque. But more bangs per second = more power. But then there’s a gearbox. So more power at the engine transfers to torque at the wheel depending on what gear ratio you’ve got.

Two cars at the same road speed, one with a diesel engine in a higher gear and one with a petrol engine at higher speed and lower gear, could move forward at the same speed when you floor the pedal.

The only difference is how you operate the gears. The reason torquey engines feel nice is that you don’t have to drop down lots of gears and have the sensation of having to work the engine to get going.

A petrol and diesel engine with the same bhp connected to appropriately geared CVTs would be indistinguisable to drive.

Car companies on mainland EU tend to use kW though, which kinda makes sense

In Spain they only really use hp, except they’re called “horses” (caballos) and not “bhp”. So my motorbike’s got 102 horses, which is nice.

A petrol and diesel engine with the same bhp connected to appropriately geared CVTs would be indistinguisable to drive.

Especially in a queue! 😉

TuckerUK – Member

No it doesn’t. It means HP measure on a chassis dynamometer (brake).

BHP means on an engine dyno surely, not chassis dyno? (if you’re taking hp from the wheel, there’s multipliers you can use to work back to crank hp but it’s a fudge…)

zokes – Member

A petrol and diesel engine with the same bhp connected to appropriately geared CVTs would be indistinguisable to drive.

Especially in a queue!
To overtake? 😆

The downside of CVT is throttle response, in my experience, so it makes overtaking slightly more challenging…

Can I be the first to mention airplanes and conveyor belts please.

It a 1 bho plane was travelling on a 1 hp conveyor belt in the direction of a horse, would it take off?