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Automotive Performance Calculators

Estimate 1/4 mile E.T from Weight and wheel HP

ET[seconds] = (Weight[lbs] / Wheel_HP) ^ (1 / 3) * 5.825

ET in seconds:

Estimate Maximum HP from Cylinder Head Flow

HorsePower = CFM * 0.2575 * Number_of_Cylinders

HorsePower:

Estimate Wheel HP From Weight and MPH

Wheel_HP = Weight[lbs] * (Trap_Speed[MPH] / 234) ^ 3

Wheel HP:

Estimate Wheel HP From Weight and ET

Wheel_HP = Weight[lbs] * (5.825 / ET) ^ 3

Wheel HP:

Estimate HP from Torque and Engine RPM

HorsePower = Torque[ft*lb] * Engine_RPM / 5252

HorsePower:

Estimate Torque from HP and RPM

Torque[ft*lb] = (5252 * HorsePower) / Engine_RPM

Torque in ft*lb:

Calculate Displacement from Bore and Stroke

Displacement[in^3] = Number_of_Cylinders * 3.14159 *(Bore[inches] / 2) ^ 2 * Stroke[inches]

Displacement in in^3:

Calculate Tire Diameter from P[section width] / [profile] R[diameter]

Diameter[inches] = Section_Width[mm] * Profile[% of Section] / 1270 + Wheel_Diameter[inches]

Diameter in inches:

Find Rear Gear Ratio

Gear_Ratio = (Tire_Diameter[inches] * Engine_RPM) / (Transmission_Ratio * MPH * 336)

Gear Ratio:

Estimate 1/4 mile ET from 1/8 mile ET

Quarter_mile_ET = Eighth_mile_ET * 1.5832

Quarter mile ET:

Calculate Piston Speed

Piston_Speed[ft/min] = Stroke[inches] * RPM / 6

Piston Speed in ft/min:

HP loss based on Elevation

HP_at_Elevation = HP_at_Sea_Level * (1 - Elevation[ft] / 1000 * 0.03)

HP at Elevation:

RPM after Shift

RPM_after_Shift = Shift_to_Ratio / Shift_from_Ratio * RPM_before_Shift

RPM after Shift:

Calculate Maximum Required CFM

Max_CFM = Max_RPM * Displacement[cubic inches] / 3456

Max CFM:

Many Thanks to Aaron Murray for compiling these equations on his site and allowing us to use them.