1. What is Dynamic Compression Ratio?

Definition: Dynamic Compression Ratio (DCR) is the actual compression ratio that occurs in an engine when the intake valve closes, accounting for real-world operating conditions.

Purpose: It provides a more accurate measure of compression than static CR for determining octane requirements and preventing detonation.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( DCR \) — Dynamic Compression Ratio (unitless)
• \( CR \) — Static Compression Ratio (unitless)
• \( IVC \) — Intake Valve Closing angle (degrees ATDC)

Explanation: The formula approximates how much the actual compression is reduced based on when the intake valve closes during the compression stroke.

3. Importance of Dynamic CR

Details: DCR is critical for engine tuning as it determines the actual cylinder pressure before ignition, affecting power, efficiency, and knock resistance.

4. Using the Calculator

Tips: Enter the static compression ratio (e.g., 10.5) and intake valve closing angle in degrees after top dead center (ATDC). The static CR must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is DCR lower than static CR?
A: Because compression doesn't begin until the intake valve closes, so some of the compression stroke is "lost."

Q2: What's a typical DCR range for pump gas?
A: Generally 7.5-8.5:1 for 91-93 octane, depending on other engine factors.

Q3: How do I find my IVC angle?
A: Check your camshaft specifications or degree the cam yourself.

Q4: Is this formula exact?
A: It's a good approximation but doesn't account for all variables like VE or pressure waves.

Q5: When would I want a higher DCR?
A: For maximum efficiency in naturally aspirated engines, but must balance with fuel octane limitations.