Understanding what’s important when climbing the hill Horsepower vs. Torque Understanding what’s important when climbing the hill

Horsepower James Watt invented the steam engine in 1775 He had trouble selling it because the standard at that time was measured by how much work a horse could do How could Watt prove that his engine could do the work that a horse could do? Watt worked backwards from known work standards for horses that kept them employed (or a much worse fate…) The standard for Horsepower became the metric HP, lifting 75kg 1 meter in 1 second

Torque vs. Horsepower

Torque Torque is a measurement of the twisting force exerted at the flywheel by the engine 1650 ft lbs equals a 1650 lb weight on a 1’ lever (or a 1 lb weight on a 1650’ lever ) (or an 825 lb weight on a 2’ lever )

Current HP measurement standards Horsepower today is calculated, not measured using a team of 505 horses Torque is measured in a dynamometer using a strain gauge RPM is available on the tachometer The formula for Horsepower is Torque x RPM/5252= HP If a 505/1650 engine produces 1633 ft lbs of torque at 1167 RPM, the formula reads as: 1633x1167/5252=333HP

Where torque matters Engine torque exerts force on the flywheel in a counterclockwise rotation “Load” meaning Vehicle weight, rolling resistance and aerodynamic resistance exert forces on the flywheel in a clockwise direction “Grade”, the percent of slope on the hill you are climbing, exerts a force on the flywheel in a clockwise fashion

Where torque matters If you have clockwise force generated by a given load and grade, you can oppose and overcome that force more readily with more TORQUE

Comparing engine outputs Here’s where it gets interesting…. A 505/1650 engine produces 1633 ft lbs of torque at 1167 RPM, the formula reads as: 1633x1167/5252=333HP A 455/1650 engine produces 1633 ft lbs of torque at 1167 RPM, the formula reads as: 1633x1167/5252=333HP A 400/1750 engine produces 1763 ft lbs of torque at 1167 RPM, the formula reads as: 1763x1167/5252=385HP

Summary Many buyers want the big HP without really understanding how HP and torque interact to provide performance High HP occurs at a point on the performance curve where you can’t really take advantage of it Higher torque provides better performance when climbing hills and has the ability to stay in high gear longer for fuel economy Operating at a lower RPM lowers parasitic loads and makes more torque available for flywheel rotation