Horsepower vs Torque Understanding whats important when climbing

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 75 kg 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: 1633 x 1167/5252=333 HP

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: 1633 x 1167/5252=333 HP • A 455/1650 engine produces 1633 ft lbs of torque at 1167 RPM, the formula reads as: 1633 x 1167/5252=333 HP • A 400/1750 engine produces 1763 ft lbs of torque at 1167 RPM, the formula reads as: 1763 x 1167/5252=385 HP

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