Share:
How It Works
This calculator covers two core engine equations. Volumetric efficiency measures how well an engine fills its cylinders relative to its displacement. Engine displacement calculates total swept volume from bore, stroke, and cylinder count. Together they let you size carburetors, compare engines, or predict airflow needs.
Example Problem
A V8 engine has a 4.00-inch bore and 3.48-inch stroke. At 5,500 RPM the airflow meter reads 320 CFM. Find displacement and volumetric efficiency.
- CID = 8 × (π/4) × 4.00² × 3.48 = 8 × 43.73 = 349.8 in³
- VE = (3456 × 320) / (349.8 × 5500) = 1,105,920 / 1,923,900 ≈ 0.575 (57.5%)
Frequently Asked Questions
What is a good volumetric efficiency for a street engine?
Naturally aspirated street engines typically achieve 80–90%. Racing engines with tuned intakes and headers can reach 95–100%. Forced-induction engines often exceed 100% because the turbo or supercharger pushes extra air in.
What does the 3456 constant represent?
It reconciles cubic feet per minute (airflow), cubic inches (displacement), and RPM. It accounts for the two-revolution cycle of a four-stroke engine: 1,728 in³/ft³ × 2 revolutions/cycle = 3,456.
How do bore and stroke affect engine character?
Over-square engines (bore > stroke) rev higher and favor horsepower. Under-square engines (stroke > bore) produce more low-end torque. A square engine balances both characteristics.
Related Calculators
- Horsepower Calculator — HP, torque, and RPM relationships.
- Gear Equations Calculator — vehicle speed from RPM, tire size, and gear ratio.
- Torque Calculator — compute rotational force from engine output.
- Horsepower from Elapsed Time Calculator — estimate HP from quarter-mile performance.
- Power Converter — convert between HP, kW, watts, and other power units.
Reference: Heywood, John B. 1988. Internal Combustion Engine Fundamentals. McGraw-Hill.