Example Data Table
| Build Type |
Intake Duration |
Exhaust Duration |
Separation Angle |
Installed Centerline |
Expected Character |
| Mild street |
260° |
266° |
112° |
108° |
Smooth idle and broad torque |
| Street performance |
280° |
286° |
110° |
106° |
Stronger midrange and overlap |
| Track focused |
300° |
306° |
108° |
104° |
Higher overlap and upper rpm power |
Formula Used
Effective intake centerline = installed intake centerline - timing set correction.
Exhaust centerline = 2 × lobe separation angle - effective intake centerline.
Intake opens = duration ÷ 2 - intake centerline.
Intake closes = duration ÷ 2 + intake centerline - 180.
Exhaust opens = duration ÷ 2 + exhaust centerline - 180.
Exhaust closes = duration ÷ 2 - exhaust centerline.
Overlap = intake opening before top dead center + exhaust closing after top dead center.
Valve lift = lobe lift × rocker ratio.
How to Use This Calculator
Enter the cam card duration values first. Add advertised duration and duration at 0.050 inch lift.
Enter lobe separation angle, installed intake centerline, and any advance or retard correction.
Leave the exhaust centerline on automatic unless your cam card lists a measured value.
Enter lobe lift and rocker ratio to estimate final valve lift.
Use optional degree wheel readings when you want to compare measured results with calculated timing.
Press Calculate. The result appears above the form and below the header.
Cam Timing Planning for Better Builds
Camshaft timing changes how an engine breathes. Intake opening, intake closing, exhaust opening, and exhaust closing decide where the power feels strongest. This calculator gives a structured view of those events. It also compares advertised timing with timing at 0.050 inch lift.
Why Valve Events Matter
The intake opening point starts cylinder filling before top dead center. The intake closing point strongly affects trapped cylinder pressure. Later closing can help higher speed airflow, but it can soften low speed response. Exhaust opening releases pressure before bottom dead center. Exhaust closing helps scavenging near overlap. Each value should match the engine, converter, gearing, compression, and intended use.
Centerlines and Separation
The intake centerline shows where the intake lobe peak sits after top dead center. A smaller intake centerline usually means the cam is advanced. A larger value usually means it is retarded. Lobe separation angle is the distance between intake and exhaust lobe peaks. Wider separation often gives smoother idle and less overlap. Narrower separation often increases overlap and a stronger idle note.
Using the Results
Enter the cam card duration values first. Then enter the lobe separation angle and installed intake centerline. Add any timing set correction if you want to test advance or retard changes. The tool estimates the exhaust centerline automatically, unless you enter a manual value. It also computes valve lift from lobe lift and rocker ratio.
Reading the Output
Use the seat timing table for general overlap and advertised valve events. Use the 0.050 inch timing table for degreeing checks and cam card comparison. A positive intake opening result is before top dead center. A negative value is after top dead center. A positive exhaust closing result is after top dead center. Negative values are before top dead center.
Practical Notes
Always verify final timing with a degree wheel, dial indicator, and the cam maker data. Small errors in pointer position or lifter setup can change readings. Check piston to valve clearance after timing changes. This calculator is for planning, comparison, and record keeping. It should not replace careful engine assembly practice. Save exported reports with build sheets so future changes stay traceable and easy to review during track testing.
FAQs
1. What does intake centerline mean?
It is the crankshaft position where the intake lobe reaches maximum lift. A smaller value usually means the cam is advanced. A larger value usually means it is retarded.
2. What does lobe separation angle show?
It shows the angle between intake and exhaust lobe peaks. Wider separation usually reduces overlap. Narrower separation usually increases overlap and can make idle rougher.
3. What is cam advance?
Cam advance means the intake centerline is lower than the separation angle. It often moves power lower in the rpm range, but every engine responds differently.
4. What is valve overlap?
Overlap is the period when intake and exhaust valves are open together. It affects idle quality, scavenging, cylinder pressure, and power range.
5. Why include 0.050 inch timing?
Timing at 0.050 inch lift is useful for comparing performance cams. It reduces confusion caused by different advertised duration checking heights.
6. Can this replace a degree wheel?
No. Use this calculator for planning and comparison. Always verify the installed cam with a degree wheel, dial indicator, and accurate pointer setup.
7. How is valve lift calculated?
Valve lift is lobe lift multiplied by rocker ratio. Real lift can change because of lash, deflection, geometry, and valvetrain setup.
8. Why enter measured valve events?
Measured events help compare degree wheel readings with calculated values. They also show whether the installed cam position matches the intended cam card setting.