In this camshaft overlap guide, we will show you how to calculate overlap in just a few seconds.
We will also help you understand what camshaft overlap is, why it matters for engine performance, fuel efficiency, and emissions, and the formula used to find it.
What is camshaft overlap?
How does it affect street engines, performance engines, and race engines?
How to calculate it step by step with examples?
We will also show you real-world applications, reference tables, and a detailed step-by-step problem solution. Find all the answers here!
Camshaft Overlap Calculator
Overlap: 0°
Camshaft Overlap Formula Explained
In camshaft design, overlap is the period when both intake and exhaust valves are open. It affects engine performance, emissions, and efficiency.
The formula to calculate overlap in crankshaft degrees is:
Overlap = (Intake Duration + Exhaust Duration) ÷ 2 – Lobe Separation Angle (LSA) × 2
- Intake Duration: The number of degrees the intake valve stays open.
- Exhaust Duration: The number of degrees the exhaust valve stays open.
- Lobe Separation Angle (LSA): Angle between intake and exhaust cam lobes.
Real-World Applications
Performance Tuning
Adjusting camshaft overlap can increase engine power at specific RPM ranges for race cars and motorcycles.
Fuel Efficiency
Optimizing overlap ensures better combustion efficiency in street vehicles, reducing fuel consumption.
Emission Control
Proper overlap timing minimizes unburnt fuel in exhaust, reducing harmful emissions.
Engine Diagnostics
Mechanics can identify camshaft issues by measuring actual overlap vs. design overlap for repair purposes.
Example Problem: Step-by-Step
Problem: An engine has intake duration of 250°, exhaust duration of 240°, and LSA of 110°. Find the camshaft overlap.
Solution:
- Step 1: Add intake and exhaust durations → 250 + 240 = 490°
- Step 2: Divide by 2 → 490 ÷ 2 = 245°
- Step 3: Multiply LSA by 2 → 110 × 2 = 220°
- Step 4: Subtract LSA×2 from average duration → 245 – 220 = 25°
- Step 5: Result → Camshaft Overlap = 25°
Camshaft Overlap Reference Table
| Engine Type | Intake Duration (°) | Exhaust Duration (°) | LSA (°) | Overlap (°) |
|---|---|---|---|---|
| Street Engine | 220 | 210 | 110 | 5 |
| Performance Engine | 250 | 240 | 112 | 33 |
| Race Engine | 270 | 260 | 108 | 67 |
| High-Efficiency Engine | 230 | 220 | 114 | 11 |
FAQs
What is camshaft overlap?
In simple words, camshaft overlap is the period when both intake and exhaust valves are open at the same time. It affects engine performance, fuel efficiency, and emissions.
What is Lobe Separation Angle (LSA)?
LSA is the angle between the peaks of the intake and exhaust cam lobes. It influences how much overlap occurs.
How does overlap affect engine type?
Small overlap → better fuel efficiency, smooth idle.
Large overlap → more power at high RPM
Can I measure overlap on a running engine?
Yes! Mechanics use a degree wheel and valve timing tools to check actual overlap against design specifications.