ONLINE CALCULATORS

Automotive Calculators - Cobranet (Bowling)
Automotive Calculators - by Bowling & Grippo

CALCULATIONS & FORMULAE

Carburetor Size (CFM)

Estimate the size carburetor required for a particular engine application.

CFM = (Engine Cubic Inches x Max RPM)/3456

Example: 609 cfm = (351 x 6000)/3456

Note: The equation above assumes 100% volumetric efficiency of the engine. An efficient race engine might only achieve a 95% VE. Street performance engines in top tune achieve 75-85% VE at best. Therefore, multiply your results above by 85% to more accurately determine the correct carburetor size. Over carburetion is the #1 mistake most people make when building an engine!

Example: 518 cfm = [(351 x 6000)/3456] x 85%

Air Filter Size

Estimate the size air filter that's required for a particular engine application.

Filter Area (sq.in.) = (Cubic Inch x Max RPM) / 25,000

Example: 84.24 sq.in. = 351 x 6000 / 25,000

Filter Height = ((Diameter x 3.14) / (Filter Area)) + .75

Example: 1.27 in. = [(14" x 3.14) / 84.24] + .75

Cylinder Volume Calculation

Determine the volume and capacity of your engine's cylinders

Area in Cubic Inches: [(radius x radius) x 3.1416] / length

Example: Ford 351C - Bore=4" Stoke=3.5"
3.5904 cu.in. = [(2 x 2) x 3.1416] / 3.5

Note: radius = bore / 2; length = stroke
For area in Gallons: divide cu.in. result by 231

Horsepower/Torque Estimate Calculation

Estimate horsepower or torque for an engine.

Horsepower = RPM x Torque / 5252
Torque = 5252 x Horsepower / RPM

Example: 249.80 hp = 5500 x 238.54 / 5252
238.54 lb/ft = 5252 x 249.8 / 5500

Rear Wheel Horsepower to Flywheel Horsepower Conversion

Convert rear wheel figures to estimate flywheel figures.

Flywheel Horsepower = FHP; Rear wheel Horsepower = RHP

FHP = RHP + 17% (auto trans)
FHP = RHP + 25% (man trans)
RHP = FHP - 15% (auto trans)
RHP = FHP - 20% (man trans)

Example: 312.25 FHP = 249.8 RHP + 62.45 HP*
* Manual trans: +25%

Intake Temperature and Horsepower Loss

Estimate power loss or gains due to air temperature changes

HP Output = +1% HP per 10 degree temperature decrease

-1% HP per 10 degree temperature increase

Example: 330 hp engine at 160° intake temp vs. 349.8 hp at 100° intake temp with cold air box

Weights and Measures

Liquid

lbs/gal

Gasoline

7.00

Milk

8.60

Water

8.33

Sea Water

8.55

Antifreeze

9.63

Oil (5w50 syn)

6.65

Lite Beer

8.44

German Beer

8.57

Alcohol

7.25

#2 Diesel Fuel

6.86

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