What is the formula for calculating indicated horsepower on a 4-stroke engine?

What is the formula for calculating indicated horsepower on a 4-stroke engine?

• A. IHP = (P × L × A × N × K) ÷ 33000
• B. IHP = (P × L × A × N) ÷ 33000
• C. IHP = (P × L × A × N × K) ÷ 30000
• D. IHP = (P × L × A × N × K) ÷ 36000

Answer: (A)

Indicated horsepower comes from how much work the cylinders can do per minute, based on the average pressure inside the cylinders, the piston motion, engine speed, and how many cylinders are firing. The work per cycle per cylinder is the mean indicated pressure P times the displaced volume of the piston, which is the piston area A times the stroke L. With a four-stroke engine, each cylinder produces a power event every two revolutions, and with K cylinders the total number of these events scales with N × K (engine speed times number of cylinders). Putting that together and converting to horsepower (the 33,000 ft-lb per minute per horsepower unit) gives the standard formula IHP = (P × L × A × N × K) ÷ 33000, where P is in psi, L in feet, A in square inches, N in rpm, and K is the number of cylinders. This is the form used here because it correctly incorporates all the essential factors for a four-stroke engine and uses the conventional unit conversion. The other options omit the cylinder count or use an incorrect divisor, which would lead to incorrect results for typical engine parameters.

Indicated horsepower comes from how much work the cylinders can do per minute, based on the average pressure inside the cylinders, the piston motion, engine speed, and how many cylinders are firing. The work per cycle per cylinder is the mean indicated pressure P times the displaced volume of the piston, which is the piston area A times the stroke L. With a four-stroke engine, each cylinder produces a power event every two revolutions, and with K cylinders the total number of these events scales with N × K (engine speed times number of cylinders). Putting that together and converting to horsepower (the 33,000 ft-lb per minute per horsepower unit) gives the standard formula IHP = (P × L × A × N × K) ÷ 33000, where P is in psi, L in feet, A in square inches, N in rpm, and K is the number of cylinders. This is the form used here because it correctly incorporates all the essential factors for a four-stroke engine and uses the conventional unit conversion. The other options omit the cylinder count or use an incorrect divisor, which would lead to incorrect results for typical engine parameters.