HP vs BHP

"ttyymmnn" (ttyymmnn) 10/09/2019 at 11:52 • Filed to: None

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My son was playing a racing game on his phone this morning, and he asked me what “BHP” stands for. I told him is means “brake horsepower,” and he asked what is the difference between that and “regular” horsepower. I did not have an answer for him, though I did a little reading this morning and have a basic concept of the difference in my head . However, c an one of you automotive geniuses provide an answer in no more than three sentences (so I can text it to him) that can be understood by 14-year-o ld?

sm70- why not Duesenberg? > ttyymmnn 10/09/2019 at 11:56

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http://mechstuff.com/what-is-brake-horsepower-bhp-vs-hp/

ttyymmnn > sm70- why not Duesenberg? 10/09/2019 at 11:57

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That’s not two or three sentences. Thanks for the link, though. I’ll check it out when I get back from teaching.

For Sweden > ttyymmnn 10/09/2019 at 11:58

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The device used to measure torque at the crankshaft is a Prony brake.

https://en.wikipedia.org/wiki/Prony_brake

“Crank horsepower” is a better term for the same measurement.

sm70- why not Duesenberg? > ttyymmnn 10/09/2019 at 12:00

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BHP is the power of the engine taken at the crank, HP is taken at the wheel and suffers some loss due to transmission and drive train resistance

diplodicus forgot his password > ttyymmnn 10/09/2019 at 12:00

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brake horsepower is horsepower measured at the crankshaft. Horsepower is measured at the wheels after drivetrain losses.

Spanfeller is a twat > ttyymmnn 10/09/2019 at 12:01

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Ask your son to move a regular chair, then a roller chair. Using the same amount of force.

Ask him: 1. Which moved faster. 2. what variable is constant and what variable changes

The constant (him) is BHP, Variable and constant (him plus the furniture) is HP... you remove the “B” after the friction losses.

The benefit of this explanation is that if you needed to move furniture; your son just did it.

jimz > ttyymmnn 10/09/2019 at 12:04

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the difference is that quoting “BHP” lets everyone know you watch Top Gear.

facw > ttyymmnn 10/09/2019 at 12:05

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I may be looking foolish here, but my understanding is that it is the power produced by the engine, before any losses from the transmission and drive system. As contrasted with wheel horsepower. Horsepower could be either.

I assume that HP numbers quoted by manufacturers are brake horsepower since it will be higher. I suspect that Top Gear, etc. talk about brake horsepower because the UK has tougher laws regarding misleading advertising than we do, so manufacturers there want to talk about brake horsepower so no one can claim they are lying about their car’s horsepower.

jimz > ttyymmnn 10/09/2019 at 12:06

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BHP: horsepower measured at the flywheel by a brake dynamometer

HP: can be synonymous with BHP in colloquial usage when talking about power at the flywheel, or can be used to indicate horsepower at the drive axle(s.)

F/RWHP: measured horsepower at the drive wheels using an inertial chassis dynamometer.

“HP” is generic, “BHP and “F/RWHP” specify how it was measured.

Chariotoflove > ttyymmnn 10/09/2019 at 12:07

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You have a unique Calvin and Hobbes father moment here, my friend. Use it wisely:

In the old days of horse-drawn buggies, sometimes the horses drawing the cart wouldn’t stop (we’ve all seen the movies with the runaway stage coach). Well, the higher end coaches had a stall built into the rear to hold a pony. If you needed emergency braking, you deployed it out the back, and it would help pull the coach to a stop by pulling in the other direction while the driver pulled on the reins. The bigger the braking pony, the more brake horsepower your coach had.

BHP

These days, the term is used instead for the extra wheel that pops down under your rear bumper and pulls in the reverse direction when you pull the emergency brake lever .

Spanfeller is a twat > diplodicus forgot his password 10/09/2019 at 12:08

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Ah shit; I got it the wrong way around 

Rusty Vandura - www.tinyurl.com/keepoppo > sm70- why not Duesenberg? 10/09/2019 at 12:29

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Well played, Sir.

Rusty Vandura - www.tinyurl.com/keepoppo > jimz 10/09/2019 at 12:30

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Colloquial usage??

!!!error: Indecipherable SUB-paragraph formatting!!!

jimz > Rusty Vandura - www.tinyurl.com/keepoppo 10/09/2019 at 12:31

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did I say something wrong?

Rusty Vandura - www.tinyurl.com/keepoppo > Chariotoflove 10/09/2019 at 12:32

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TheSleepingTiger > sm70- why not Duesenberg? 10/09/2019 at 12:32

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That's incorrect

Rusty Vandura - www.tinyurl.com/keepoppo > Spanfeller is a twat 10/09/2019 at 12:32

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“Which moved with less effort?” might be better worded.

Rusty Vandura - www.tinyurl.com/keepoppo > jimz 10/09/2019 at 12:32

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But what if I don’t want people to know that?

TheSleepingTiger > ttyymmnn 10/09/2019 at 12:43

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Horsepower taken at the wheel is WHP. Brake Horsepower is an engines power without power loss, such as an alt or p/s pump. HP is engine power as it would sit in a car.

Spanfeller is a twat > Rusty Vandura - www.tinyurl.com/keepoppo 10/09/2019 at 12:43

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I wanted to keep the force applied constant, to underline that identical engines perform differently depending on the drivetrain. 

Rusty Vandura - www.tinyurl.com/keepoppo > Spanfeller is a twat 10/09/2019 at 12:49

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Oh, okay; I guess I can still stamp your homework then.

Spanfeller is a twat > Rusty Vandura - www.tinyurl.com/keepoppo 10/09/2019 at 12:51

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thank you mister- sir.

Snuze: Needs another Swede > jimz 10/09/2019 at 12:59

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This is the most correct answer here. 

VajazzleMcDildertits - read carefully, respond politely > For Sweden 10/09/2019 at 13:36

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I’ve seen crank hp and bhp numbers be off by a little bit on the same drivetrain and not due to testing variance . I think they are measured just slightly differently enough to confuse everyone.

I just take crank hp and subtract 1% just to make things harder on myself. 

CRider > sm70- why not Duesenberg? 10/09/2019 at 13:41

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That’s wheel horsepower and nobody rates cars that way. Except by some tuner shops, you’ll never see that advertised.

VajazzleMcDildertits - read carefully, respond politely > CRider 10/09/2019 at 13:51

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The issue that is confusing everyone is that people started slapping in hp for both crank or wheel hp, and that bhp takes account some of the drivetrain loss, while hp calculations are all over the place, not to mention switching to metric also creates OTHER numbers that cast doubt that you’re actually reading anything useful at all when you see the letters HP.

There is so much inconsistency about bhp vs hp that tbh at this point it’s going to matter more about context than what it actually means, since the official definition has been muddied by time and misuse.

BHP and crank hp should be the same but they’re off a lot of the time, because it depends on the context of who’s doing the reporting/calculations.

Snuze: Needs another Swede > ttyymmnn 10/09/2019 at 14:20

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In casual usage there is no difference . Brake horsepower is the correct term for power as measured, but it’s just not commonly referred to as such. I suspect manufacturers don’t typically advertise “Brake Horsepower” because consumers are stupid and don’t care how much power their brakes make , they only want to know how much power the engine makes!  

Okay, but seriously, i n engineering terms there’s a difference because we might talk about brake horsepower (as measured) vs some othe theoretical number such as calculated or simulated horsepower (purely mathematical) or indicated horsepower (extrapolated from a pressure measurement) . In particular, i ndicated horsepower is still somewhat common and is a number calculated as a function of chamber pressure (measured) and cylinder volume. Engineers use a tool called an “engine indicator” to measure chamber pressure in a test engine, hence the term . Since indicated horsepower is a calculation based on a simgle measurement of cylinder pressure, it doesn’t take into account friction in the engine, nor the interacting affects of multiple cylinders (in a multi-cylinder engine).

What other people here are discussing is “crank/flywheel horsepower” vs. “ wheel horsepower”, which are both forms of brake horsepower since both are measured on a brake.

TheSleepingTiger > Spanfeller is a twat 10/09/2019 at 15:22

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Your example is not accurate. You've described the difference between HP and WHP, not BHP and HP.

Spanfeller is a twat > TheSleepingTiger 10/09/2019 at 16:06

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What do you even mean with “as it sits”?

TheSleepingTiger > Spanfeller is a twat 10/09/2019 at 18:34

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I never said "as it sits" in the comment you replied to. In my other comment "as it sits" means with all the accessories the engine would power (alt, power steering, air pump, etc). 

Spanfeller is a twat > TheSleepingTiger 10/09/2019 at 18:55

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Meh, you’re right about the WHP part... I could be pedantic and claim that my frame of reference was “the car’s output” vs the “engine output” 

Though BHP depends on whether you’re using SAE or DIN

TheSleepingTiger > Spanfeller is a twat 10/09/2019 at 19:31

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The frame and unit of measure makes no difference. The difference between HP and WHP is everything from the flywheel/flexplate to the tires/ground. The difference between BHP and HP is all the things attached to the engine which the engine must power but does not contribute to the movement of the vehicle.

CRider > VajazzleMcDildertits - read carefully, respond politely 10/10/2019 at 00:19

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BHP does not take drivetrain loss into account. BHP is a measure of power at the engine’s crank while the engine has no accessories (belts, alternator, ect..) attached to it that can sap power. BHP is the highest rating an engine will achieve. It doesn’t help the confusion when you explain the definition and you don’t know what it actually means. 

VajazzleMcDildertits - read carefully, respond politely > CRider 10/10/2019 at 01:38

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I wrote it in haste while in the middle of something else and swapped the two terms. The definitions were posted all over the place. They don’t let you edit anything after 15 minutes, which was well before you pointed it out. Sorry I didn't catch it in time? I hardly think my one typo is going help or hurt any confusion. No ones going to be using me as their reference. 

Dino Dino Bambino > Rusty Vandura - www.tinyurl.com/keepoppo 10/10/2019 at 05:17

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Here’s some interesting reading:

http://www.angelfire.com/my/fan/Horsepower.html

dogisbadob > For Sweden 10/10/2019 at 10:49

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My Little Prony :p

Curtzx9r > For Sweden 10/10/2019 at 11:13

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Lold, brake horse power is an actual measurement of how much braking power the car has like to stop its wheels so Horsepower makes you go and brake horsepower makes you stop this gives you ideas on car handling and is very important to people buying big trucks say you buy a new Ford f350 and it had a 6.7 diesel it nay have 740 Hp and 850 BHP thatvway you can stop whatever trailer your towing full of horses down a mountain.

So Horsepower HP, crank horsepower CHP , and WHP wheel horsepower which is measured literally at the wheels of your car... note significant loss of horsepower after going through transmission, drive line and axles/differential typically 10 to 15% but all these measure what gets you moving but BrKe Horsepower is the measurement of how much braking force your vehicle has. I'm a genius write me with any questions in life curtzx9r@yahoo.com 

simpleKyle > ttyymmnn 10/10/2019 at 11:49

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Brake h orsepower is the amount of horsepower that the engine produces at the crank, i.e. before being connected to the transmission and drivetrain.

B.hp is always higher because of the losses derived through friction and inertia required to rotate the drivetrain.

Hp is how much horse power actually makes it to the drive wheels resulting in the true force used to move the vehicle.

Jaden > ttyymmnn 10/10/2019 at 13:03

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Brake horse power refers to an engine directly attached at the crank to a Dyno, so it is crank horse power. Where as most after market hp testing is done on a wheel horse power dynomom eter which has drivetrain loses and is typically less than an engine Dyno due  to lost power through the transmission, driveling and rear end .