Compression Ratio Calculator
The Compression Ratio Calculator determines an engine's compression ratio from swept volume (displacement) and clearance volume (combustion chamber). Optimize your engine build for power, efficiency, and fuel octane requirements.
🕐 Recent Calculations
What is Compression Ratio?
Compression ratio is the ratio of the total cylinder volume (when the piston is at bottom dead center) to the clearance volume (when the piston is at top dead center). A 10:1 compression ratio means the air-fuel mixture is compressed to 1/10th of its original volume before ignition.
Higher compression ratios increase thermal efficiency and power output but require higher octane fuel to prevent detonation (knock). Stock gasoline engines typically run 9:1 to 12:1. Diesel engines use 14:1 to 25:1 because diesel fuel ignites through compression alone.
Wzory i Zastosowane Równania
Kalkulator opiera się na 5 podstawowych równaniach:
1 Compression Ratio ▼
A cylinder with 500cc swept volume and 55cc clearance: CR = (500 + 55) / 55 = 10.09:1.
2 Swept Volume (Single Cylinder) ▼
Bore = 86mm, Stroke = 86mm: V = 0.7854 × 86² × 86 = 499.6 cc.
3 Clearance Volume from CR ▼
To achieve 9.5:1 with 500cc displacement: CV = 500 / (9.5 - 1) = 58.82 cc.
Jak Korzystać z Kalkulatora
Aby skorzystać z tego kalkulatora stosunku, wykonaj 3 proste kroki:
Wprowadź Dane
Wpisz znane wartości w pola wejściowe. Jedno pole pozostaw puste — jest to niewiadoma, którą obliczy kalkulator.
Wybierz Tryb
Wybierz tryb pracy — Rozwiązywanie proporcji, Upraszczanie lub Skalowanie. Każdy tryb stosuje inne równania.
Odbierz Wynik
Kliknij Oblicz. Ekran wyników wyświetla odpowiedź wraz z kolorowym paskiem stosunku, wykresem kołowym oraz objaśnieniem kroku po kroku.
Przykłady Zadań z Rozwiązaniami Krok po Kroku
Oto 3 przykładowe zadania z pełnym opisem kroków matematycznych w tym kalkulatorze:
Wejście 1 Engine with 600cc displacement and 60cc chamber
Wejście 2 Calculate displacement for 88mm bore, 82mm stroke
Wejście 3 Find clearance volume for 12:1 CR, 450cc displacement
Najczęściej Zadawane Pytania
What compression ratio is best for pump gas (87 octane)? ▼
For 87 octane regular gas, stay at or below 9.5:1 static compression ratio. Modern engines with direct injection and variable valve timing can safely run 10:1 to 11:1 on regular fuel.
How does compression ratio affect horsepower? ▼
Each 1-point increase in compression ratio typically yields 3-4% more power, up to a limit. Going from 9:1 to 10:1 might add 10-15 HP on a 300 HP engine. Beyond about 13:1, gains diminish and knock risk increases.
What is the compression ratio of a diesel engine? ▼
Diesel engines run 14:1 to 25:1 compression ratios. The high compression heats air enough to ignite diesel fuel without spark plugs. Modern common-rail diesels typically use 16:1 to 18:1.
How do I measure clearance volume? ▼
Fill the combustion chamber with fluid (isopropyl alcohol or light oil) through a burette with the valves closed and piston at TDC. The volume of fluid needed equals the clearance volume. Typical values range from 40-70cc.
Does milling the head increase compression ratio? ▼
Yes. Milling (shaving) the cylinder head reduces clearance volume, increasing compression ratio. Removing 0.020 inches from the head surface typically raises CR by 0.3-0.5 points depending on chamber size.