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.
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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.
القوانين والمعادلات المستخدمة
تستخدم Compression Ratio Calculator هذه 5 معادلات أساسية:
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.
كيفية استخدام هذه الحاسبة
لاستخدام حاسبة النسب هذه، اتبع 3 خطوات بسيطة:
أدخل القيم
اكتب قيم النسبة المعروفة في حقول الإدخال. اترك حقلاً واحداً فارغاً — هذا هو المتغير المجهول الذي تحله حاسبة النسب.
اختر الوضع
حدد وضع النسبة — حل، تبسيط، أو تغيير الحجم. يطبق كل وضع معادلات مختلفة على قيم الإدخال الخاصة بك.
احصل على النتائج
انقر فوق احسب. تعرض شاشة النتائج الإجابة مع شريط نسبة مرئي، ومخطط دائري، وتفصيل حل خطوة بخطوة.
أمثلة على مسائل وحلول خطوة بخطوة
فيما يلي 3 مسائل توضيحية مع حلول مفصلة خطوة بخطوة باستخدام حاسبة النسب هذه:
المدخلات 1 Engine with 600cc displacement and 60cc chamber
المدخلات 2 Calculate displacement for 88mm bore, 82mm stroke
المدخلات 3 Find clearance volume for 12:1 CR, 450cc displacement
الأسئلة الشائعة
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.