Auto Formulas

# gradient("Auto Formulas and Calculators", 0xFF0000, 0x000000)

Please note: these formulas are for estimating only. Contrary to popular belief, using this site will not increase your horsepower.
 •ET from HP •HP from ET •HP from MPH •HP from Torque •Torque from HP •Max HP from CFM •in³ to Liter •Liter to in³ •Displacement (standard) •Displacement (metric) •HP/ET Chart •1/8 to 1/4 mile ET •1/4 to 1/8 mile ET •Piston Speed •Find RPM from Piston Speed •Find Gear Ratio •Find Tire Diameter •Find RPMs •Find Trans Ratio •Find MPH •Tire Diameter •HP Loss @ Elevation •Max CFM Needed •Volumetric Efficiency •rpm after shift •Street Carb CFM •Racing Carb CFM •Wheel Thrust •G (force) •Weight Transfer •Lateral Acceleration •Lateral Weight Transfer •Centrufugal Force •Driveshaft Torque •Drive Wheel Torque •Complete List of Formulas
Estimate E.T. from Weight (lbs.) and wheel HP
 Weight: Wheel HP: ET in seconds:

ET from HP (1/4 mile) = (WEIGHT / HP)^.333 * 5.825

Estimate Maximum H.P. from Cylinder Head Flow
 CFM: Number of Cylinders: Flywheel HP:

HP = CFM x 0.2575 x number of cylinders

Estimate wheel H.P. from Weight (lbs.) and M.P.H.
 Weight: Trap Speed (MPH): Wheel HP:

HP from MPH (1/4 mile) = WEIGHT * (MPH/234)^3

Estimate wheel H.P. from Weight (lbs.) and E.T.
 Weight: ET in seconds: Wheel HP:

HP from ET (1/4 mile) = WEIGHT * (5.825/ET)^3

Estimate H.P. from Torque and RPMs
 Torque: RPMs: HP:

HorsePower = TORQUE * RPM / 5252

Estimate Torque from HP and RPMs
 HP: RPMs: Torque:

TORQUE = (5252 * HP) / RPM

Rear-Wheel HP Required to push your brick through the quarter mile
This chart was borrowed and modified from http://www.jason.fletcher.net/tech/combos/et_hp.htm

Use the chart below to see how much wheel horsepower is required to run the elapsed time you want.

 ET & SPEED (seconds @ mph) VEHICLE WEIGHT (pounds) 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 16.0 @ 85 116 125 135 145 154 164 174 183 193 203 15.5 @ 88 127 138 149 159 170 180 191 202 212 223 15.0 @ 91 141 152 164 176 187 199 211 223 234 246 14.5 @ 94 156 169 182 194 207 220 233 246 259 272 14.0 @ 97 173 187 202 216 230 245 259 274 288 303 13.5 @ 101 193 209 225 241 257 273 289 305 321 337 13.0 @ 105 216 234 252 270 288 306 324 342 360 378 12.5 @ 109 243 263 283 304 324 344 364 385 405 425 12.0 @ 114 275 297 320 343 366 389 412 435 458 480 11.5 @ 119 312 338 364 390 416 442 468 494 520 546 11.0 @ 124 356 386 416 445 475 505 535 564 594 624 10.5 @ 130 410 444 478 512 546 580 615 649 683 717 10.0 @ 136 474 514 553 593 632 672 712 751 791 830 9.5 @ 143 553 599 645 692 738 784 830 876 922 968 9.0 @ 151 651 705 759 813 868 922 976 1,030 1,084 1,139 8.5 @ 160 772 837 901 965 1,030 1,094 1,159 1,223 1,287 1,352 8.0 @ 170 926 1,004 1,081 1,158 1,235 1,312 1,390 1,467 1,544 1,621

Calculate Cubic Inches from Liters
 Liters: # of Cylinders: Cubic Inches: Cubic Inches per Cylinder:

1 Liter = 61.02374 Cubic Inches

Calculate Liters from Cubic Inches
 Cubic Inches: # of Cylinders: Liters: Liters per Cylinder:

1 Cubic Inch = 0.016388 Liters

Calculate Displacement from Bore and Stroke (inches)
 Bore (inches): Stroke (inches): # of Cylinders: Cubic Inches: Cubic Inches per Cylinder: Liters: Liters per Cylinder:

Displacement (in^2) = Number Of Cylinders * 3.14159 * (Bore/2)^2 * Stroke

Calculate Displacement from Bore and Stroke (metric)
 Bore (millimeters): Stroke (millimeters): # of Cylinders: Cubic Inches: Cubic Inches per Cylinder: Liters: Liters per Cylinder:

Displacement (in^2) = Number Of Cylinders * 3.14159 * (Bore/2/25.4)^2 * Stroke/25.4

Calculate Tire Diameter
 Section Width (P275/40R17): Profile (P275/40R17): Wheel Diameter (inches) (P275/40R17): Diameter (inches):

Diameter (in.)=(((section width * profile)/2540) + (wheel diameter/2)) * 2

Find Rear Gear Ratio
 RPMs: Tire Diameter (inches): Transmission Gear Ratio: MPH: Rear Gear Ratio:

Rear Gear Ratio = (Tire Diameter * RPM) / (Trans Ratio * MPH * 336)

Find Tire Diameter (inches)
 RPMs: Rear Gear Ratio: Transmission Gear Ratio: MPH: Tire Diameter (inches):

Tire Diameter = (Trans Ratio * MPH * 336 * Rear Gear Ratio) / (RPM)

Find RPMs
 Tire Diameter (inches): Rear Gear Ratio: Transmission Gear Ratio: MPH: RPMs:

RPM = (Trans Ratio * MPH * 336 * Rear Gear Ratio) / (Tire Diameter)

Find Transmission Gear Ratio
 RPMs: Rear Gear Ratio: Tire Diameter (inches): MPH: Transmission Gear Ratio:

Trans Ratio = (Tire Diameter * RPM) / (Rear Gear Ratio * MPH * 336)

Find MPH
 RPMs: Rear Gear Ratio: Transmission Gear Ratio: Tire Diameter (inches): MPH:

MPH = (RPM * Tire Diameter) / (336 * Rear Gear Ratio * Trans Ratio)

Find 1/4 mile ET from 1/8 mile ET
 1/8 ET: 1/4 ET:

1/4 mile ET = 1/8 mile ET x 1.5832

Find 1/8 mile ET from 1/4 mile ET
 1/4 ET: 1/8 ET:

1/8 mile ET = 1/4 mile ET / 1.5832

Calculate Piston Speed
 Stroke (inches): RPMs: Speed (Feet/Minute): Speed (Feet/Second):

piston speed in fpm = stroke in inches x rpm / 6

Calculate RPM from Piston Speed
 Stroke (inches): Piston Speed (FPM): RPM:

RPM = piston speed in fpm x 6 / stroke in inches

HP loss based upon elevation
 Elevation (feet): HP @ Sea Level: HP Loss: HP @ Elevation:

bhp loss = elevation in feet / 1000 x 0.03 x bhp at sea level

RPM After Shift
 Shift from Ratio: Shift to Ratio: RPM Before Shift: RPM After Shift:

rpm after shift= ratio shift into / ratio shift from x rpm before shift

Calculate Maximum CFM Needed
 Max RPM: Displacement (inches^3): Max CFM Needed:

Theoretical cfm = rpm x displacement / 3456

Volumetric Efficiency
 Theoretical CFM: Actual CFM: Volumetric Efficiency:

Volumetric Efficiency = acutal cfm / theoretical cfm x 100

Street Carb CFM Needed
 Max RPM: Displacement (inches^3): CFM Needed:

Street carb cfm = rpm x displacement / 3456 x 0.85

Racing Carb CFM Needed
 Max RPM: Displacement (inches^3): CFM Needed:

Racing carb cfm = rpm x displacement / 3456 x 1.1

Drive Wheel Torque
 Flywheel Torque: Transmission Gear Ratio: Rear Gear Ratio: Drive Wheel Torque:

drive wheel torque = flywheel torque x trans gear x final drive x 0.85

Wheel Thrust
 Drive Wheel Torque: Rolling Radius (inches): Wheel Thrust:

wheel thrust = drive wheel torque / rolling radius

G Force
 Wheel Thrust: Weight: G Force:

g (force) = wheel thrust / weight

Weight Transfer
 Weight: CG Height (inches): Wheelbase (inches): G (force): Weight Transfer:

weight transfer = weight x cg height / wheelbase x g

Lateral Acceleration
 Radius (feet): Time (seconds): Lateral Acceleration:

Lateral Acceleration = 1.227 x radius / time^2

Lateral Weight Transfer
 Weight: CG Height (inches): Wheel Track (inches): G Force: Lateral Weight Transfer:

lateral weight transfer = weight x cg height / wheel track x g

Centrufugal Force
 Weight: G Force: Centrufugal Force:

centrufugal force = weight x g

Driveshaft Torque
 Flywheel Torque: Transmission Ratio: Driveshaft Torque:

driveshaft torque = flywheel torque x transmission ratio

```Here is a list of formulas:			[back to top]
•Rear Gear Ratio = (Tire Diameter * RPM) / (Trans Ratio * MPH * 336)
•Tire Diameter = (Trans Ratio * MPH * 336 * Rear Gear Ratio) / (RPM)
•RPM = (Trans Ratio * MPH * 336 * Rear Gear Ratio) / (Tire Diameter)
•Trans Ratio = (Tire Diameter * RPM) / (Rear Gear Ratio * MPH * 336)
•MPH = (RPM * Tire Diameter) / (336 * Rear Gear Ratio * Trans Ratio)
•Tire Diameter (inches) = (((section width * profile) / 2540) + (wheel diameter / 2)) * 2
•HorsePower = TORQUE * RPM / 5252
•TORQUE = (5252 * HP) / RPM
•1 Liter = 61.02374 Cubic Inches
•Displacement (in^2) = Number Of Cylinders * 3.141592653589 * (Bore/2)^2 * Stroke
•HP from MPH (1/4 mile) = WEIGHT * (MPH/234)^3
•HP from ET (1/4 mile) = WEIGHT * (5.825/ET)^3
•ET from HP (1/4 mile) = (WEIGHT / HP)^.333 * 5.825
•HP from cylinder head intake flow  = CFM x 0.2575 x number of cylinders
•1/4 mile ET = 1/8 mile ET x 1.5832 (prestage.com)
•1/8 mile ET = 1/4 mile ET / 1.5832 (prestage.com)
•piston speed in fpm = stroke in inches x rpm / 6
•rpm = piston speed in fpm x 6 / stroke in inches
•bhp loss = elevation in feet / 1000 x 0.03 x bhp at sea level
•theoretical cfm = rpm x displacement / 3456
•volumetric efficiency = acutal cfm / theoretical cfm x 100
•street carb cfm = rpm x displacement / 3456 x 0.85
•racing carb cfm = rpm x displacement / 3456 x 1.1
->Formulas for g force & weight transfer
•drive wheel torque = flywheel torque x trans gear x final drive x 0.85
•wheel thrust = drive wheel torque / rolling radius
•g (force) = wheel thrust / weight
•weight transfer = weight x cg height / wheelbase x g
•lateral acceleration = 1.227 x radius / time^2
•lateral weight transfer = weight x cg height / wheel track x g
•centrufugal force = weight x g
->Formulas for shift points
•rpm after shift = ratio shift into / ratio shift from x rpm before shift
•driveshaft torque = flywheel torque x transmission ratio
->Formulas for weight distribution
•percent of weight on wheels = weight on wheels / overweight x 100
•increased weight on wheels = [ distance of cg from wheels / wheelbase x weight ] + weight
->Formulas for center of gravity
•cg location behind front wheels = rear wheel weights / overall weight x wheelbase
•cg location off-center to heavy side = track / 2 - [ weight on light side / overall weight ] x track
•cg height = [ level wheelbase x raised wheelbase x added weight on scale / distance raised ] x overall weight

Check out Prestage.com for more useful formulas.

email me at aaronmurray@msn.com if you have any formulas you would like to see
added (as a calculator) or if you have any suggestions.
```