Bhp and hp difference

[Tvec22]

I couldn't find a thread on this so... Whats the difference between Bhp and Hp? Is there a difference? Thank you in advance.

 

[Punknoodle]

There is no difference, it is merely different terminology, although usually BHP is referring to engine power, and HP is power at the wheels.

The Brake in Brake Horse Power (BHP) refers to the measuring equipment used to measure power at the engine.

EDIT: I thought I'd quickly explain why power at the engine is different than power at the wheels - when the power is sent through the drivetrain (you know, like clutch, driveshaft, diff etc etc) and the wheels, power is lost due to the effort required just to turn these components, and so generally power at the wheels can be up to around 40% less than power at the engine. 4WDs generally have more losses as they have more drivetrain, if you know what I mean.

 

[AOS-]

So 1 HP = 1 BHP?

 

[Punknoodle]

So 1 HP = 1 BHP?

If referring to power at the same point, yes.

 

[niky]

When people are referring to HP, they're usually talking about BHP. Power at the wheels is usually signified as WHP.

 

[Jim Prower]

Well, it gets a LOT more complex than that...

BHP is the standard UK measure of horsepower. In the U.S., you have SAE Net and SAE Certified, which are slightly different tests and give slightly different results from BHP. Then you have PS - Japan and Germany use this rough Metric equivalent for HP, and most of Europe uses the same measure with a different name. The Australians, Chinese, and much of the Pacific Rim use Kilowatts, the actual Metric Power rating, which makes it hard to compare directly many of those cars to the Horsepower or PS used in much of the world...and if you talk pre '70s American cars, you get into the SAE Gross test, which resulted in inflated ratings of more than 40HP in some cases. All of these are measured at the crank.

Then we have WHP, or "true" HP, which is typically found by a rolling road. This is actually what's being transmitted to your tires in a gear that results in a ratio very close to 1:1, typically fourth. This is usually about 15%-25% less than the rating at the crank.

Finally, there's "Fiscal" horsepower, or CV, which isn't really a measure of power at all, but is a rating applied for taxing purposes in France and Italy.

 

[niky]

Unfortunately, many marketing departments confuse PS with HP... Since they're so similar, they simply translate them 1:1 between regions in marketing literature... big fib, really.

 

[Eric.]

PS and HP are so close that it hardly matters though. The Veyron is rated 1001PS/987BHP I think.

 

[Tornado]

PS and HP are so close that it hardly matters though. The Veyron is rated 1001PS/987BHP I think.

And even then, neither number is accurate anyways, as its all relative to how truthful the manufacturer is.

 

[Sniffs]

the difference for both BHP and PS is like 1.5 % from horsepower. so it's barely noticable except around 3-400

note that there is a BIG difference with the three ways that HP was measured in the states, though

SAE Gross horsepower (muscle era and earlier, i believe) was measured with no drag on the engine from things like the alternator, etc.
SAE Net was with all that stuff on

i just looked it up. there's a rating style for every country, situation, standard, and engine type. so you might as well forget it.

 

[niky]

PS and HP are so close that it hardly matters though. The Veyron is rated 1001PS/987BHP I think.

Close isn't close enough if we're talking advertising. Marketing people know that people pay attention to peak numbers, even if you and I know that they count for very little compared to actual performance... and a 3-5 hp difference can sometimes help sell a car.

Even worse when they double dip it. Mistakenly translate from one to the other on a 1:1 basis, then retranslate. Which somehow gave our local 1.8 Corolla 140 hp, with the exact same engine and mapping as the 126 hp engine in all other "global" Corollas back in the 00's.

 

[Mike0105]

If I remember correctly, 10PS = 9.9bhp. I know that 138bhp is advertised as 140ps from VW and KIA 2.0 diesels.

It is worth noting that advertised bhp is not always what you get. Fiat are often conservative in this. The 150 bhp T-jets have been known to be closer to 170 bhp on rolling roads.

 

[niky]

Advertised is often a minimum guarantee, given normal conditions. It gets even more complicated when you have turbo units that can adjust for atmospheric conditions... Which means that many turbo cars make more power on the dyno than they supposedly should given quoted power and atmospheric conditions. This is ignoring, of course, cars which are purposely under-rated for various reasons (Skyline GT-R, Dodge SRT4, etcetera).

And then there are the cars which pull back power when they detect abnormal conditions, such as a mismatch in front and rear wheel speeds (on a 2WD dyno) or a hot engine bay resulting from heat soak on the dyno. The old M3 was notorious for this, and certain Mazdas pull power on the dyno (current NC MX5) by retarding the timing.

Then we get into the question of actual drivetrain losses as opposed to assumed...

 

[Zenith]

WHP=Car's output at the wheels.
HP=Engine's output at the flywheel. Rarely important.

Take all ratings from manufacturers with a grain of salt, many lie.

 

[Famine]

the difference for both BHP and PS is like 1.5 % from horsepower

BHP is horsepower. The first response got this pretty much bang on.


BHP (Brake Horsepower) is measured on a bench. The engine's not in the car - the "B" comes from equipment which brakes the crank to measure load. The units of BHP are poundfeet per second (lbft/s) and 1BHP = 550lbft/s.

Horsepower is measured wherever and whenever. Engine horsepower ratings are usually a backwards fudge from wheel horsepower (wheel power is always lower than engine power on the same car, due to effort required to drive powertrain/drivetrain components - gearbox and shafts). The units of horsepower are also poundfeet per second (lbft/s) and 1hp = 550lbft/s.


That pretty much covers what's been asked. However, both BHP and hp are used in the majority of the English-speaking world so, for the rest of the world...

Metric horsepower is usually named "horse power" in the European languages to which the ratings apply - and they are rarely used outside of non-English-speaking countries. There's the German PS (pferdensterke), the French ch (chevaux), the Spanish CV (Caballos de vapor), the Swedish hk (hästkraft) and a whole host of others, including pk, CP, hv, KS, k, LE, KM and I'm sure I've forgotten some. All Metric Horsepowers are rated in kilogrammetres per second (Nm/s) however they are measured and all have 1 unit equal to 75kgm/s.

Australia and New Zealand use the SI unit of Watts to measure vehicle power. There's very little to say about them - they're measured as above and have the unit of watts, which are defined as 1 Joule per second, and usually car engines are rated in kilowatts (kW). In fact almost all non-US cars use kilowatts as a power rating and their regional preferences are applied as a supplemental power rating for clarity - it's actually a law in the EU that kW is the primary measure of power and all others are supplemental only*...


1hp (550lbft/s) = 1BHP = 1.014PS (or equivalent unit) = 746W
1PS (75kgm/s) = 0.986hp = 0.986BHP = 735W
1kW = 1.34hp = 1.34BHP = 1.36PS (or equivalent unit)


The keen-eyed amongst you will note that the horsepower units are measured in units of torque (kgm or lbft) per second. This should then generate the usual arguments of which is better, torque or power, whereby someone will talk about towing a trailer as an example of why torque is king and someone else will talk about F1 cars as an example of why torque is irrelevant - and someone will inevitably say that "power is how fast you hit the wall and torque is how far you move it" - but they are directly related to each other and through gearing (gears step up/down torques, but don't affect power aside from the load of driving the gearbox) you can have lots of both.


*There's a certain historical irony that James Watt endeavoured to create the unit of "horsepower" through experimentation with actual horses, as his - and others' - steam engines were replacing horses in industry and a comparison was required for marketing information - and then 200 years later the European Union decides that the unit is anathema to them and replace it with a unit named after James Watt!

 

[Sniffs]

lets just say every country has its own spec when it comes to work measurement.

 

[Famine]

They do, but they all fall into one of Imperial horsepower (1 = 550lbft/s), metric horsepower (1 = 75kgm/s) or SI power (1 = 1kW).

 

[Moot]

You may like to know 1 horsepower is the same as 178 calories/second.
Now you know how many Mars bars you need to put in your tank.

 

[Rotary Junkie]

You may like to know 1 horsepower is the same as 178 calories/second.
Now you know how many Mars bars you need to put in your tank.

That's a lot of Mars Bars.

 

[Luminis]

That's a lot of Mars Bars.

Now, imagine if humans could digest fuel... A sip and you'll probably be able to keep on running for weeks

 

[AlexGTV]

WHP is what should concern consumers?

 

[Rotary Junkie]

WHP is what should concern consumers?

WHP is what is displayed in the performance of the car (or rather average WHP through all gears) but BHP is how everything ever will be rated and is generally more consistent than WHP ratings.

 

[AlexGTV]

^And that is because bhp is taken before gears right?

 

[Rotary Junkie]

No, it's because engine dynos are a lot more consistent and a lot easier to control testing conditions with.

 

[AlexGTV]

I'm going to start a business then for consistent and reliable "wheel dynos". Immediate patenting and the fact that it would give the best measure for real performance would create a competitive advantage and result in mass demand by car companies, tuning firms and others, for the seal of approval.

 

[Punknoodle]

It's because there are so many more variants involved with running on a roller dyno. You can get hub dynos which bolt onto your hubs once the wheels are removed, they are generally used in high horsepower applications where the car can slip on the rollers, but obviously they take longer to set up, but remove at least the tire variations.

In all seriousness though, it doesn't matter if the dyno doesn't stay consistent to the exact measurement as cars themselves will vary their output depending on a number of factors like fuel and temperature, and will likely not output the same each time.

The guys that go to dyno comps, they have a lot of tricks up their sleeves to get the highest number they can on the day, but on a hot day in traffic, there is no way it'll be performing the same way.

After all, that is why it doesn't really matter, all that matters is how much fast it has when you press the go pedal!

 

[niky]

That's a lot of Mars Bars.

Once did the calculation (sadly now lost) as to how much it would cost you to bike a certain distance at a certain speed if your "fuel" was US-priced Big Macs. Turns out, it's still cheaper to buy gas and scoot there.

----

Yup... Dynos suck. So many ways to cheat, especially with a sweep test on a roller dyno... it's not funny...

 

[Mike0105]

Once did the calculation (sadly now lost) as to how much it would cost you to bike a certain distance at a certain speed if your "fuel" was US-priced Big Macs. Turns out, it's still cheaper to buy gas and scoot there.

Not too mention the new liver you would need if you kept it up for a while !