Cam Overlap

Cam Overlap Formula:

\[ \text{Overlap} = \text{Intake Duration} + \text{Exhaust Duration} - (2 \times \text{LSA}) \]

Intake Duration (degrees):

Exhaust Duration (degrees):

LSA (lobe separation angle, degrees):

Valve Overlap:

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1. What is Cam Overlap?

Cam overlap refers to the period in degrees of crankshaft rotation when both the intake and exhaust valves are open simultaneously in an internal combustion engine. This overlap period is crucial for optimizing engine performance, particularly at high RPM.

2. How Does the Calculator Work?

The calculator uses the cam overlap formula:

\[ \text{Overlap} = \text{Intake Duration} + \text{Exhaust Duration} - (2 \times \text{LSA}) \]

Where:

\( \text{Intake Duration} \) — Duration of intake valve opening in degrees
\( \text{Exhaust Duration} \) — Duration of exhaust valve opening in degrees
\( \text{LSA} \) — Lobe separation angle in degrees

Explanation: The formula calculates the angular period during which both intake and exhaust valves remain open simultaneously, which affects engine scavenging and performance characteristics.

3. Importance of Cam Overlap Calculation

Details: Proper cam overlap calculation is essential for engine tuning, affecting torque characteristics, power band, emissions, and overall engine efficiency. Different overlap values are optimal for different engine applications (street, race, etc.).

4. Using the Calculator

Tips: Enter intake duration, exhaust duration, and lobe separation angle in degrees. All values must be positive numbers. Typical values range from 200-300° for duration and 100-120° for LSA.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical overlap range for street engines?
A: Street engines typically have overlap between 10-50 degrees, providing a good balance between low-end torque and high-RPM power.

Q2: How does overlap affect engine performance?
A: More overlap generally increases high-RPM power but reduces low-end torque. Less overlap improves low-end torque but may limit top-end power.

Q3: What is lobe separation angle (LSA)?
A: LSA is the angle in crankshaft degrees between the maximum lift points of the intake and exhaust lobes. It significantly influences overlap and engine characteristics.

Q4: Can overlap be negative?
A: Yes, negative overlap occurs when the exhaust valve closes before the intake valve opens, common in some performance and racing cams.

Q5: How does overlap affect emissions?
A: Excessive overlap can increase hydrocarbon emissions as unburned fuel may escape through the exhaust valve during the overlap period.