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HISTORY OF HORSEPOWERIN THE BEGINNING GOD CREATED THE HORSE. No Wait ! The Pony ! To be more precise, the pit pony. Yes race fans, our obsession with horsepower may have started with miniature horses or pit ponies. Back in the day, coal was removed from mines with miniature horses or pit ponies. In the late 18th century, James Watt was working on improving the 50 year old Newcomen steam engine. Watt improved the steam engine so much that he is one of the guys credited with starting the industrial revolution. He is so highly regarded that the term "watt" was named after him. Watt was trying to market his revamped steam engine and wanted a way to compare it to the current engine of the day, the Horse. Watt observed that a pit pony accomplishes three tasks. The pony pulls a load of coal out of the mine over a certain distance over a certain length of time. And that's the formula. Force (Torque) X Time (RPM) / distance (5252)= Horsepower. Watt was the first one to use the term Horsepower. Watt then took the results from his pit pony observations and judged that a horse was 50% stronger than a pony and doubled his findings and came up with this: A strong horse can lift 550 lbs, 1 foot in one second or 33,000 foot pounds per minute. Watt then stated that one horsepower is equivalent to 33,000 foot pounds of work per minute. Now in order to convert this to our Dyno we do this: measure the weight at one foot out from the center of the Dyno (ft/lb). We then compute the distance traveled in one revolution. 6.2832 feet (Pi* a two foot circle). So we have done 6.2832 foot pounds of work per revolution. Now we go back to Watt, he said that 33,000 foot pounds of work per minute equals one horsepower. If we divide the 6.2832 foot pounds of work done per revolution into 33,000 foot pounds, we come up with the fact that one foot pound of torque at 5252 RPM is equal to 33,000 foot pounds of work per minute and this is one horsepower. WHY DO DYNO REPORTS VARYDynos are precise. Our Dyno can measure 1 tenth of 1 horsepower. What's not precise is the internal combustion engine and the effects that weather, external conditions, internal conditions have on it. For this reason, all Dynos use many correction factors. The weather correction factor is the most commonly understood. Weather conditions play a huge roll on the internal combustion engine. Air pressure, air temperature, humidity etc. Most boaters know that an engine is going to require more fuel at sea level than at 6000 ft. For this reason Dyno operators use a weather correction factor adopted from aviation. What this does- sets a baseline for what it calls a standard day which is a barometer of 29.92 and a temperature of 60 F. Before an engine is run on the Dyno, the operator will adjust the Dynos computer to the current barometer setting and current temperature. The Dynos computer will take the current settings and compare them to the standard day figures and come up with correction amount. Then add or subtract from the raw Torque to arrive at the corrected Torque and Horsepower figures. Dyno facilities are all at different elevations thus different air pressures. The air pressure adjustments are extremely sensitive and can effect the correction value considerably. Air temperature plays a big roll in the engines ability to make Torque. Dyno cell configuration and how the air flows across the engine or like our Dyno, the inlet air can be isolated from the cell air. Another variable. Fiction correction factor. Another variable. Inertia correction factor. Another variable. All these correction factors are compiled and produce a final correction value, adding or subtracting from the raw Torque and displaying the Corrected Torque and Corrected Horsepower figures. The Dyno figures between facilities will vary because of the nature of correction factors and Dyno cell setups. So if you want to see how much Horsepower that tunnel ram set up has over that big four barrel carburetor, take your engine to guy that originally Dyno Tuned your engine.
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