# Engine Horsepower

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Engine horsepower, abbreviated as EHP, is the estimate of engine horsepower after a quarter mile run using the trap speed.

## Engine Horsepower formulas

 $$\large{ EHP = W \; \left( \frac{ v }{ 234 } \right) ^3 }$$ $$\large{ EHP = \frac{ W }{ \left( \frac{ ET }{ 5.825 } \right) ^3 } }$$ (elapsed time) $$\large{ EHP = W \; \left( \frac{ s }{ 234 } \right) ^3 }$$ (trap-speed) $$\large{ EHP = \frac{ \tau \;\; s \;(RPM) }{ 5252 } }$$ (rotating horsepower) $$\large{ EHP_{change} = W \; \left( \frac{ v_2 }{ 234 } \right) ^3 \;-\; W \; \left( \frac{ v_1 }{ 234 } \right) ^3 }$$ (determine increase in horsepower) $$\large{ EHP_{change} = \frac{ W }{ \left( \frac{ ET_2 }{ 5.825 } \right) ^3 } \;-\; \frac{ W }{ \left( \frac{ ET_1 }{ 5.825 } \right) ^3 } }$$ (determine increase in horsepower with ET)

### Where:

 Units English Metric $$\large{EHP}$$ = engine horsepower $$\large{\frac{lbf-ft}{sec}}$$ $$\large{\frac{Btu}{s}}$$ $$\large{ET}$$ = elapsed time (time to finish quarter mile) $$\large{sec}$$ $$\large{s}$$ $$\large{ET_1}$$ = initial elapsed time (time to finish quarter mile) $$\large{sec}$$ $$\large{s}$$ $$\large{ET_2}$$ = final elapsed time (time to finish quarter mile) $$\large{sec}$$ $$\large{s}$$ $$\large{s}$$ = speed $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$ $$\large{ \tau }$$  (Greek symbol tau) = torque $$\large{lbf-ft}$$ $$\large{N-m}$$ $$\large{v}$$ = velocity $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$ $$\large{v_1}$$ = initial velocity $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$ $$\large{v_2}$$ = final velocity $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$ 