Question.

"norskracer98-ExploringTheOutback" (norskracer98) 08/27/2014 at 22:40 • Filed to: None

1

20

Whats the difference between crank, wheel, and brake horse power? Ive heard all three so please enlighten me.

Jedidiah > norskracer98-ExploringTheOutback 08/27/2014 at 22:43

8

Crank is measured at the crank of the engine before the loss of the transmission is applied.

Wheel horsepower is measured at the drive wheels by a rolling road dyno.

Brake horsepower is a more complicated definition

Brake horsepower (bhp) is the measure of an engine's horsepower before the loss in power caused by the gearbox and drive train. In Europe the DIN standard tested the engine fitted with all ancillaries and exhaust system as used in the car. The American SAE system tests without alternator, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc. so the figures are higher than the European figures for the same engine. Brake refers to the device which was used to load an engine and hold it at a desired rotational speed. During testing, the output torque and rotational speed were measured to determine the brake horsepower .

-Wikipedia

Arch Duke Maxyenko, Shit Talk Extraordinaire > norskracer98-ExploringTheOutback 08/27/2014 at 22:43

0

Crank is measured at the crank with or without accessories, brake is the same with accessories and wheel is measured at the wheel.

Biggus Dickus (RevsBro) > norskracer98-ExploringTheOutback 08/27/2014 at 22:44

0

My understanding is brake and crank are the same: what the engine puts out at the crankshaft. Wheel, is at the tires. Its always lower because of friction (ex. Energy is lost in the transmission and diff to heat, noise, etc.)

norskracer98-ExploringTheOutback > Arch Duke Maxyenko, Shit Talk Extraordinaire 08/27/2014 at 22:45

0

What do you mean by accessories? Other parts of the car?

TurboSloth > norskracer98-ExploringTheOutback 08/27/2014 at 22:45

1

Disclaimer: I'm not an engineer.

Basically, what I think is, that the difference is where they measure HP. I think Brake HP and Wheel HP are the same (both are measured at the wheels and are a figure of how much power the car puts down to the road), while Crank HP is measured at the transmission (flywheel I think). I think that Crank HP would be higher because its closer to where the power is being produced (since I think there would be some energy lost when traveling to the wheels.)

Again, I'm not an engineer, I'm merely speculating. Someone want to tell me if I was close to being right?

Arch Duke Maxyenko, Shit Talk Extraordinaire > norskracer98-ExploringTheOutback 08/27/2014 at 22:46

0

a/c, power steering, etc...

norskracer98-ExploringTheOutback > Arch Duke Maxyenko, Shit Talk Extraordinaire 08/27/2014 at 22:47

0

Ok, thanks.

thebigbossyboss > TurboSloth 08/27/2014 at 22:48

0

Something like that I think (also not an engineer).

I do know that physics make it impossible not to lose some HP at the wheels as the power is transferred. No device is mechanically 100% efficient.

OkCars- 22k Crossroads > norskracer98-ExploringTheOutback 08/27/2014 at 22:49

0

This is my understanding

Crank =brake horse power =hp

Wheel horse power is after all the hp losses through the drivetrain. And it is measured in the dynos.

tromoly > norskracer98-ExploringTheOutback 08/27/2014 at 23:00

0

To expand on Arch Duke's response, it all comes down to inertial losses. At the crank without accessories, that's the most "pure" power being produced since there's nothing to rob energy aside from the components needed to make power. At the other end of the spectrum, power at the wheels includes all the losses from accessories (AC, alternator, power steering, etc), driveline (transmission/transfercase, driveshafts/hafshafts, axles), and tires.

So TL;DR version, crank power is highest, wheel power lowest.

Jedidiah > norskracer98-ExploringTheOutback 08/27/2014 at 23:06

1

To elaborate on my previous post.

Crank and wheel horspower only designate where the the horsepower value is calculated or measured.

Brake horsepower refers to a measurement that uses a device called a brake designed to hold an engine at a certain rpm. Brake horsepower can vary depending on the engineering standard used.

Horsepower measurements are generally optimistic. Brake and Crank hp can be off by up to 40% due to loss caused by the transmission. Wheel HP can also have noticeable percent error depending on the the engineering standard used since atmospheric corrections are idealistic. The temperature of the dyno room will also affect the measurement.

For example, SAE gross hp measurements allow long tube headers to be fit to a engine, which will give a higher rating than expected.

Since the SAE definition of brake horsepower does not require a water pump, they often use external cooling systems to cool the engine. Thus, the coolant temperature can affect horsepower ratings.

In a factory engine, you will pretty much always make less horsepower than the factory rating.

To further the discrepancies, indicated horsepower is a theoretical value and who knows how truthful the manufacturer is with their calculations, which are too idealized.

norskracer98-ExploringTheOutback > tromoly 08/27/2014 at 23:06

0

Does that but BHP in the middle?

tromoly > norskracer98-ExploringTheOutback 08/27/2014 at 23:33

0

To my understanding yes, however I haven't used it personally so I could be wrong.

Jayhawk Jake > norskracer98-ExploringTheOutback 08/27/2014 at 23:40

0

Yes. BHP is the intermediate step before adding drivetrain losses to get to wheel horsepower

crowmolly > Jedidiah 08/28/2014 at 08:40

0

The American SAE system tests without alternator, water pump, and other auxiliary components such as power steering pump,

Eh? That sounds a lot like SAE Gross which hasn't been used since the early 70's

crowmolly > norskracer98-ExploringTheOutback 08/28/2014 at 08:59

0

Crank HP is the horsepower measured at the crankshaft, before drivetrain losses from the transmission, differential, etc. This is typically measured on an engine dyno.

Wheel HP is the horsepower measured at the tire and takes into account the aforementioned drivetrain. This is typically measured on a chassis dyno.

The term "brake" refers to the type of dyno used to hold the engine during hp testing . I *think* BHP testing includes a flywheel where SAE crank testing does not but I am not sure on that part. You can test for both Brake Net and Brake Gross HP.

Gross is a measurement of crank HP that does not include accessories like smog pumps, alternators, exahust systems, etc.

Net is a measurement of crank HP that is supposed to be representative of the power the engine will put out as-installed in a car.

FWIW Wikipedia does not have its shit straight on this topic.

crowmolly > TurboSloth 08/28/2014 at 09:01

0

Nope. Brake and wheel are not the same. Engines are not rated at the factory "at the wheels".

Crank HP is measured at the crank and there *may* be a flywheel involved.

Crank HP is higher then wheel HP since there is no drivetrain losses.

Jedidiah > crowmolly 08/28/2014 at 11:28

0

Yep. That's American Brake Horsepower.

The American version even lets you test it with long tube headers.

crowmolly > Jedidiah 08/28/2014 at 12:20

0

Not according to the SAE. Attached is a copy of part of J1349. You do not have to have the actual part on the car but the simulated load may need to be there. Unless I am reading the standard wrong.

To further complicate things, you can use a chassis dyno to get hp the wheels via a water brake. Attached is one from Taylor.

http://www.taylordyno.com/products/chass…

Jedidiah > crowmolly 08/28/2014 at 12:43

0

As far as I know, J1349 is a net horsepower measurement that is taken at the crank.

I think the difference lies with the term "brake horsepower." The European definition of bhp coincides with what Americans define as net horsepower standards like J1349.

I'm not too knowledgeable about these specific standards.