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Horsepuppy

Tips and Recommendations from Guru Mike Nixon

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mikenixon
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Horsepuppy

#1

Post by mikenixon »

Gritty grudge night under arc light at the local track. Rough, creosote-covered-wood benches in the moonlight on the edge of town. Fuel, oil, rubber, and unwashed bodies-- smells that frame the night. Wonderfully elemental mechanical sounds; shatteringly violent, threatening, primeval, haunting. Boiling the testosterone. Drag racing! Horsepower heaven!

At the onset of the industrial revolution, one "horsepower" was declared equal to 550 pounds moved one foot in one second. Thus power is not a single thing, but a combination of three things: force, distance and time. Whether the electromotive force (EMF) in "voltage" or in an engine's combustion, force is frequently measured in terms of pressure. Force is the first building block of power.

Distance, power's second ingredient, is at work in the engine's piston stroking down the cylinder. Combine these two, force and distance, and we get work. A very useful thing, work. However, it's still not power.

Finally, we add the time element. Time is very important. In an engine, time looks like revolutions per minute. An engine that made its peak power at 5,000 rpm, a four-stroke and thus pulsing every other revolution, would produce 2,500 power pulses a minute. If this engine developed 476 ft-lbs of work (3.5" piston being pushed 4.25" by 140 psi mean combustion pressure) and we multiplied that by 2,500 pushes, its power output would be some 1,190,000 ft-lbs per minute.

Wow. An ungainly number. Doesn't sound familiar either, does it? However, it takes 33,000 ft-lbs/minute to make one horsepower, so simple division nets us our final goal, 36 horsepower, about the advertised umph of a modern 300cc streetbike.
Last edited by mikenixon on Thu Jan 21, 2021 8:05 pm, edited 1 time in total.
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Re: Horsepuppy

#2

Post by Rat »

Poetry in motion ...

Gord anim-cheers1
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Re: Horsepuppy

#3

Post by gltriker »

Mike, I owned a 1953 HD Servi-car many years ago. In an old HD owners manual the venerable sidevalve 45 c.i. engine was rated at 15 taxable horsepuppies.
Exactly, what, is a taxable horsepower?

Interesting fact.
The standard cast iron cylinder head , factory installed on the Servi-car engine , provided a compression ratio of 4.5 to 1.

The aluminum cylinder head found on the 2 wheel bikes 45 c.i. engines provided a 6 to 1 compression ratio. :shock:
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Re: Horsepuppy

#4

Post by mikenixon »

Re taxable horsepower, some countries do that, tax the vehicle based on the manufacturer-documented power. Just an income deal, I think. It's still being done. There is a code in every VIN that communicates it.

Wow. Servicars. MMI used to have an "Early Model" H-D class. I never owned a meter maid sickle, but I sure saw a lot of them at the downtown L.A. Harley shop when I was a teenager. Always intigued me.
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Re: Horsepuppy

#5

Post by Sugs »

I'm always fascinated by why certain numbers are settled upon instead of others. So why 550lbs? Instead of say 500lbs, 100lbs or 1000lbs.
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Re: Horsepuppy

#6

Post by digger »

I love the opening paragraph Mike, boy, does that bring back some memories. You capture the imagination, then thrill us with your knowledge. A good read. :)
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Re: Horsepuppy

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Post by mikenixon »

:)
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Re: Horsepuppy

#8

Post by Shadowjack »

I only faintly recall this story about how horsepower was originally measured, but in the days when they used ponies to pull mine carts out of a coal mine, the carts weighed so much and the ponies walked a certain distance to get them up. I envision a rope and pulley arrangement, but that's just me. Weight times distance over time gives you the figure of mechanical equivalence (of an average pony).
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Re: Horsepuppy

#9

Post by sgwilly »

The thing about physics is you can even talk to aliens about it.
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Re: Horsepuppy

#10

Post by 5speed »

another interesting read..
is there a difference between horsepower and "brake horsepower". Brits use that term..
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Re: Horsepuppy

#11

Post by sgwilly »

BHP is measured at the crankshaft (and is what is typically listed by manufacturers). HP is measured at the rear wheel (or I guess driven wheel). That measurement is always quite disappointing by comparison. I remember my MGB has 30 hp at the rear wheel. When you imagine 30 actual horses - OK! When you think of your lawnmower - not so much.

https://www.youtube.com/watch?v=ybP-hweOq7A
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Re: Horsepuppy

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Post by mikenixon »

5speed wrote: Fri Jan 22, 2021 10:07 am another interesting read..
is there a difference between horsepower and "brake horsepower". Brits use that term..
"Brake" is an engineering term originally meaning "measured" (technically, a dynomometer is called a "brake"), but as willy pointed out, it came later to refer to "at the crankshaft" and in reality it's virtually always computed and not measured. Not because crank dynos aren't used, they are, but in powersports they're much rarer than rear wheel dynos, more common in the auto trade. Having spent a considerable portion of my working years at manufacturer's corporate offices and thoroughly trained by the manufacturers, I can say with confidence they never think or talk in terms of rear wheel horsepower. It's only the end user, including race shops, that do. So one more of those things where the manufacterer and the customer talk different languages. And thus the war/debate that seems to rage between the validity of the two methods. They are both valid, with different purposes. And after all, the most common use of a dyno at the consumer level is more as a comparator anyway, not as an absolute measurer.

The next question that comes up is how much loss is there in the transmission and drivetrain. Again, that's unimportant unless you're comparing rear wheel to crankshaft, and the shop with the dyno bay doesn't care about that, only in before and after readings, at least not in powersports. Fifteen to twenty-five percent are popular assumptions for the loss in powersports, varying with the type of drive and other factors.

Something you might find more interesting is brake and chain problems show on a dyno. You can inuit their causing losses, and you can even read those losses on the dyno graph.

I worked in a speed shop years ago that had engine pieces still embedded in the ceiling. And I once built a big inch Harley that on the dyno failed the only original part left in the buildup, the lifters.
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Re: Horsepuppy

#13

Post by 5speed »

digger wrote: Thu Jan 21, 2021 10:04 pm I love the opening paragraph Mike, boy, does that bring back some memories. You capture the imagination, then thrill us with your knowledge. A good read. :)
I agree... we had a spring ritual here called "the may run". It was the first drag race of the season and happened in Prince Edward Island..
Friends, camping and the races.. anim-cheers1
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Re: Horsepuppy

#14

Post by mikenixon »

:) I just realized I forgot to add the smell of race gas to the backdrop...
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Re: Horsepuppy

#15

Post by digger »

Ah yes, when the top fuel guys came to the track, the distinctive smell of nitromethane fuel in the air, and that burning sensation in my eyes. Good times were had by all.
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