Pete Stanisavljevich wrote:
> Listers,
>
> I've always heard figures of "power loss" through a drive line of 5% to 25%
>and
> I always wondered where does this figure come from? Has anybody does a
> measurement?
>
> < Larry Wright 'snip >
>
>
> Maybe Laifman, or somebody can offer up an explanation. I just can see that
>much
> power being gobbled up.
>
> Peter S.
> B9471799
O.K., Pete,
I'll take a gross cut at it. I think the 'drive train loss' statement, while
correctly included, is not the whole story.
If you ever look at car specifications, you just might see things like SAE Gross
Horsepower, SAE Net Horsepower, DIN Horsepower (German standards), and British
Taxable Horsepower.
Well, there are horses, and then there are HORSES,
Let's take the easiest, and most fun one first, British Taxable Horsepower:
If there is anything we can learn from the British, it's there love for raising
taxes. If it weren't for this tendency, we never would have had the Boston Tea
Party, over an increase in the tax on tea, and the American Revolution would
never
have happened, and we would be drinking expensive tea with breakfast, rather
than
expensive coffee. The British have also taxed such things as owning a radio,
having a TV antenna, having a window. I have actually seen London Town Homes
with
bricked-up windows to avoid the tax. They are killing Scotland with the Tax on
Scotch. That's just plain mean! Now in the car area, they wanted to have a
'graduated' tax system, so they decided to tax "Horsepower". Well, the tax
people
were not too bright, technically, and some long-haired professor told them that
the
BMEP (Brake Mean Effective Pressure) that pushes down the piston is a constant,
and
horsepower is strictly a function of bore size. So, applying this rule
rigorously,
they devised a formula that used the bore and number of cylinders to arrive at a
"Taxable Horsepower", and that's it. So that's why you see British cars with
12 to
40 horsepower, and know that can't be true. And this is why the English cars
have
such long strokes. Cubic inches makes horsepower, as well as good breathing,
and
there is no 'constant BMEP'.
SAE Gross Horsepower:
This is not exact, so anybody with the SAE standards book can fill in the
nitty-gritty, but basically the horsepower in this configuration is done at a
specified ambient pressure, temperature, and is measured at the flywheel with
such
horsepower diminishing 'accessories' as air conditioning pumps and fans, power
steering, smog pumps, alternators, fans, fuel pumps, water pumps, air cleaners
removed or replaced by external drivers. This, then, is the "Advertised
Horsepower", and is naturally the greatest. It also, of course ignores any
losses
through manual (low) or automatic (moderate) transmissions, rear ends, and
frictional losses in the drive train, or air resistance to the rotating tires,
or
road wheel losses to the dynamometer.
SAE Net Horsepower:
This also ignores any drive train losses, but rightly so as they should be a
function of application and vary so much, but does require that the normal
'accessory' equipment, like water pumps, fuel pumps, some alternator load be
included. I do believe that power steering, air conditioning are still not
present. This is measured at the flywheel as well.
So, bottom line, there is a very big difference between what's "advertised", and
what you really get. My 1949 Olds 88 convertible, the first with the Kettering
V-8, was put on a chassis dynamometer, and the advertised 135 horsepower came
out
100 at the rear wheels. In a Chevrolet convertible body, weighing in at an
astonishing 4,000 lb.., it was still the hottest stock car on the road when I
had
in in 1950. And the 35% drop was right there.
Hope that helps some.
Steve
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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