Top Gear

[Ms. Denmark]

So Mr. Man has been watching Top Gear for a while now (Netflix) and I sat down to watch with him and have a question. What is the difference between American horsepower and British brake horsepower? Mr. Man thought it might be where the HP is measured from but isn't sure about the specifics. Anybody out there in Marauderland have a simple concise answer.:)

[Bluerauder]

So Mr. Man has been watching Top Gear for a while now (Netflix) and I sat down to watch with him and have a question. What is the difference between American horsepower and British brake horsepower? Mr. Man thought it might be where the HP is measured from but isn't sure about the specifics. Anybody out there in Marauderland have a simple concise answer.:)

Both refer to power at the crank.

Here is some additional info .....

According to the most common definition of horsepower, one horsepower is defined as exactly:

1 hp = 745.69987158227022 W

The horsepower was first used by James Watt during a business venture where his steam engines substituted horses. It was defined that a horse can lift 33,000 pounds with a speed of 1 foot per minute: 33,000 ft-lbf-min-1. This is roughly equivalent to lifting 147,000 Newtons (the weight of a 15,000 kg mass) at a speed of 0.005 metre per second. [1] (http://www.web-cars.com/math/horsepower.html)


brake horsepower (bhp)

Brake horsepower was a term commonly used before the 1970s in the United States, and is still common in the United Kingdom. It indicates the brake, the device for measuring the true power of the engine. Stating power in 'bhp' gives some indication this is a true reading, rather than a calculated or predicted one. However, several manufacturers started to strip their engines of essential ancillaries for the purposes of getting a high horsepower figure to use in marketing the car.

hp (SAE)

In the United States the term fell into disuse after the American Society of Automotive Engineers (SAE) recommended manufacturers use "hp (SAE)" to indicate the power of the engine, given that particular car's complete engine installation. This may also be stated as "SAE net hp" or simply "net hp". The British market seemed not to need the correction.

[SpartaPerformance]

There is no difference, as stated above they like to specify that the HP ratings are at the crank so they will say brake horse power or BHP.

[ChiTownMaraud3r]

Brake horsepower as in a load being applied to the engine itself.

[thathotrodlincn]

In my opinion, horsepower is not a measurable quantity. It is defined as the product of torque and engine rpm. the governing equation is 2PiFLN/33000 where Pi is the mathmatical constant 3.1415926535xxxxxxx FL is the observed torque and N is the engine speed in RPM. The 33000 represents the defined expression of 1 hprsepower as lifting 33000 pounds 1 foot in 1 minute. There are 2 horsepowers for a given engine, indicated horseppwer which is based on the average positive (or mean effective) pressure acting on the piston through the power stroke, and brake horsepower as generated by the engine as measured by a Prony (spelling is correct) brake using the above equation. The equation for indicated horsepower is PLAN/33000 where Pis the indicated mean effective pressure, L is the stroke length, A is the piston area, and N is the engine RPM. Indicated horsepower or IHP is always higher than brake horsepower or BHP. The Prony brake is an antiquated device developed in the early days of the internal combustion engine. Modern devices for determining engine torque may be some form of pump, or electrical device developing a varing measurable resistence imposed in the item whose torque is being determined. Therefore the brake horsepower of an engine is the useful horsepower being developed at the flywheel of an engine.

[Fosters]

Since you mentioned top gear, you gotta count in the idiot factor. They call a dyno a "rolling road", and when they put a car on the dyno, if it doesn't meet the manufacturer claims (at the crank), they claim it either lost it or it's false advertisement, or whatever. This was the case when they reviewed the first GT500, and it made 441rwhp. They made fun of it because it wasn't 500hp... :rolleyes:

They rarely do that with newer cars though, usually with older cars to see how much they "lost" over the years...

[Jesse]

I love that show! They were in Intercourse PA for the new season! Lancaster county is like an hour or two from here. I wish I would have known.

[SID210SA]

In my opinion, horsepower is not a measurable quantity. It is defined as the product of torque and engine rpm. the governing equation is 2PiFLN/33000 where Pi is the mathmatical constant 3.1415926535xxxxxxx FL is the observed torque and N is the engine speed in RPM. The 33000 represents the defined expression of 1 hprsepower as lifting 33000 pounds 1 foot in 1 minute. There are 2 horsepowers for a given engine, indicated horseppwer which is based on the average positive (or mean effective) pressure acting on the piston through the power stroke, and brake horsepower as generated by the engine as measured by a Prony (spelling is correct) brake using the above equation. The equation for indicated horsepower is PLAN/33000 where Pis the indicated mean effective pressure, L is the stroke length, A is the piston area, and N is the engine RPM. Indicated horsepower or IHP is always higher than brake horsepower or BHP. The Prony brake is an antiquated device developed in the early days of the internal combustion engine. Modern devices for determining engine torque may be some form of pump, or electrical device developing a varing measurable resistence imposed in the item whose torque is being determined. Therefore the brake horsepower of an engine is the useful horsepower being developed at the flywheel of an engine.


I was told pretty much the same thing by a tuner here in San Antonio.

[napolitano]

That show is awesome.