Re: bhp, SAE vs DIN (inputs needed)

[bearbvd@domain.elided (Greg Hermann)]

>Brian Shorey wrote:
>>i heard that all of the american hp figures were derived from running motors
>>on dynos with no accessories bolted on them.  while i don't think that would
>>account for 150 hp, it would certainly explain some of the difference
>>between quoted vs actual hp.
>
>I believe this is the difference between SAE vs DIN horses.  Anyone care to
>elaborate on the difference in measurement methodology?
>
>On the same track, why is there a "b" infront of the "hp"?
>
>Someone told me it stood for "brake" - from the old days, when you had
>1 horsepower transport (and rode on the left of the road, too bad if you were
>sinistere), it was derived from the effort to stop a standard wheel turning
>at a certain angular velocity.

You are correct on b meaning brake, the term indicates running the engine
against  any sort of a brake, most likely a water brake. It is in contrast
to "Indicated" horsepower, which is a more theoretical number.

There are both SAE net and gross horsepower testing and correction
procedures, and I have little doubt that the standards for determining each
have evolved over time.  I would not be surprised to see a correction for
even the power used by the OIL pump in a past or present version of the SAE
gross standard. There is also a DIN testing standard which is analogous to
the SAE net standard, not sure whether DIN has an analogue to the SAE
gross.

There is also a "metric" horsepower unit which is slightly different from
the British/American one. The British HP is equal to 550 foot pounds per
second (also equal to 72,000 stone furlongs per fortnight).

Best approach, if you are curious as to actual test conditions and
corrections which get applied to actual measured dyno reading results per
the various standards, would be to get a copy of the standard(s). SAE can
be found at <sae.org>, I am sure that DIN has a web site as well, although
I have never looked for it. Atmospheric
pressure/temperature/density/humidity is one factor which is standardized,
engine cooling method is another, exhaust piping is yet another. The goal
of the standards is not so much optimistic advertising as it is to give
folks a way to obtain reproducible test results in different test labs.

Of course, as usual, the marketing folks have used the various numbers as
they saw fit to sell stuff to the gullible members of the public! Kinda
funny how the American big three switched from advertising SAE gross to net
(much lower) numbers when the insurance industry began setting rates based
on HP to weight ratio in the early seventies!

Regards, Greg

>
>Cheers
>Lawrence

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