Automotive Engineering Calculators
These calculators help engine builders and enthusiasts plan changes: engine displacement from bore, stroke and cylinder count, static compression ratio from chamber, gasket, deck and piston volumes, horsepower from torque and rpm or estimated from vehicle weight and quarter-mile results, and road speed in each gear from rpm, gear ratios, final drive and tire size.
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All Automotive (4)
Engine Displacement Calculator
Engine displacement from bore, stroke and cylindersCompression Ratio Calculator
Static compression ratio from bore, stroke and chamber volumesHorsepower Calculator
Horsepower from torque and RPM, or from weight and quarter-mileGear Speed Calculator
Vehicle speed per gear from RPM, ratios and tire size
Which tool do I need?
Find the displacement of an engine after a rebore
Enter the new bore, stroke and cylinder count to get cc, litres and cubic inches.
Check compression after changing the head gasket
Enter the chamber, gasket, deck and piston volumes to get the static compression ratio.
See what speed each gear gives at redline
Enter the gear ratios, final drive, tire size and rpm to get the speed in every gear.
About Automotive
Inputs work in millimetres or inches and cc or cubic inches. The quarter-mile horsepower methods are empirical estimates and are labelled as such; a dynamometer gives the real figure. For tire diameter changes, use the Tire Size Calculator in Everyday Calculators.
Changing compression, gearing or power affects reliability, emissions and legality. Treat these results as planning numbers and check with a qualified engine builder.
Guides
- Engine Displacement Explained: Bore, Stroke, CC and Cubic InchesHow swept volume comes from bore and stroke, why a 0.030 in overbore adds five cubic inches to a 350, what bore/stroke ratio says about an engine, and the rounding that makes a 1998 cc engine a "2.0".
- Static vs Dynamic Compression Ratio: How to Calculate BothEvery volume in the clearance space, the sign convention for dished and domed pistons, how intake closing sets dynamic compression, and what pump fuel tolerates.
- Estimating Horsepower from Quarter-Mile ET and Trap SpeedWhere the Hale, Fox and Huntington constants come from, why trap speed is a better power gauge than elapsed time, how drivetrain loss links wheel and crank figures, and how hp, kW and PS relate.
- Road Speed from RPM, Gear Ratio and Tire Size: The FormulaFrom the 336 constant to metric tyre codes: how rpm becomes road speed through gearbox, final drive and tyre, the rpm drop between gears, and speedometer error.
Frequently asked questions
Why do torque and horsepower curves cross at 5,252 rpm?
Horsepower equals torque in pound-feet times rpm divided by 5,252, so at exactly 5,252 rpm the two numbers are equal when plotted in those units.
What is the difference between static and dynamic compression ratio?
Static compression uses the full stroke. Dynamic compression accounts for the intake valve closing after bottom dead centre, which shortens the effective compression stroke and is closer to what the engine experiences.
How accurate is horsepower from a quarter-mile time?
It is an estimate based on empirical formulas, usually within about 10% for typical cars. Traction, gearing and weather all affect the time, so trap speed is usually a better predictor than elapsed time.
How do I convert engine cc to cubic inches?
Divide cubic centimetres by 16.387, the number of cc in one cubic inch. A 5,000 cc engine is about 305 cubic inches.