1. What is a Compression Ratio Calculator?

Definition: This calculator determines the compression ratio of an engine based on swept volume and clearance volume.

Purpose: It helps engine builders and performance enthusiasts calculate the compression ratio which affects engine performance and fuel requirements.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( CR \) — Compression Ratio (dimensionless)
• \( V_s \) — Swept volume (piston displacement) in cubic inches
• \( V_c \) — Clearance volume (combustion chamber volume) in cubic inches

Explanation: The total cylinder volume at bottom dead center (swept + clearance) is divided by the volume at top dead center (clearance only).

3. Importance of Compression Ratio

Details: Compression ratio affects engine efficiency, power output, fuel requirements, and octane tolerance. Higher ratios generally mean more power but may require higher octane fuel.

4. Using the Calculator

Tips: Enter swept volume (cylinder displacement) and clearance volume (combustion chamber volume). Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical compression ratio for street engines?
A: Most street engines run between 8:1 and 10:1, while high-performance engines may go up to 12:1 or higher.

Q2: How do I measure clearance volume?
A: Use a burette to measure liquid volume in the combustion chamber with piston at TDC and spark plug installed.

Q3: Does this include head gasket volume?
A: Head gasket volume should be included in your clearance volume measurement.

Q4: What's the maximum safe compression ratio for pump gas?
A: Typically 9.5:1 for 87 octane, 10.5:1 for 91 octane, and 11.5:1 for 93 octane, depending on engine design.

Q5: How does compression ratio affect horsepower?
A: Generally, each point of compression ratio increase can provide 3-4% more power, all else being equal.