Camshaft Timing Calculator
*Use values measured at 0.050″ lift for standard comparison. If an event occurs on the opposite side of TDC/BDC than standard, enter as a negative number.
Camshaft Specifications
Intake Duration:
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Exhaust Duration:
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Intake Centerline (ICL):
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Exhaust Centerline (ECL):
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Lobe Separation Angle (LSA):
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Valve Overlap:
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Understanding Camshaft Timing
Camshaft timing is a critical aspect of engine building that dictates when the valves open and close in relation to the position of the pistons. Correctly dialing in your cam timing can significantly alter the power curve of your engine, optimizing it for low-end torque or high-RPM horsepower.
Key Definitions
- Intake Centerline (ICL): The point of maximum lift on the intake lobe, measured in crankshaft degrees After Top Dead Center (ATDC). Advancing the cam (lower ICL number) generally shifts the power band lower in the RPM range.
- Lobe Separation Angle (LSA): The number of degrees between the intake centerline and the exhaust centerline. A tighter LSA (e.g., 108°) increases overlap and tends to produce a "choppier" idle and peakier power band, while a wider LSA (e.g., 114°) smooths the idle and spreads power over a wider range.
- Duration: The total time, measured in crankshaft degrees, that the valve is off its seat. This calculator generally assumes inputs based on 0.050″ lift figures, which is the industry standard for comparing camshaft profiles.
- Overlap: The period where both intake and exhaust valves are open simultaneously. This occurs at the end of the exhaust stroke and the beginning of the intake stroke. High overlap aids in cylinder scavenging at high RPM but kills low-speed drivability and vacuum.
How to Degree a Cam
To use this calculator effectively, you should be in the process of "degreeing" your camshaft. This process ensures the cam is installed exactly as the manufacturer intended, or modified to suit your specific needs.
- Find True TDC: Use a piston stop and a degree wheel to find accurate Top Dead Center.
- Measure Events: Using a dial indicator on the lifter, measure the crank angle at which the valve reaches 0.050″ lift on the opening ramp and 0.050″ lift before closing on the closing ramp.
- Input Data: Enter these four values (Intake Open, Intake Close, Exhaust Open, Exhaust Close) into the calculator above.
- Analyze: Compare the calculated Intake Centerline to the "Installed Centerline" on your cam card. If your calculated ICL is lower than the spec, the cam is advanced. If it is higher, the cam is retarded.
Common Cam Timing Adjustments
Most aftermarket timing sets allow you to adjust the cam position relative to the crank.
- Advancing the Cam (e.g., +4°): Opens the intake valve sooner. This increases low-end torque, improves throttle response, and lowers the RPM at which peak power occurs. It also increases dynamic compression.
- Retarding the Cam: Opens the intake valve later. This shifts the power band higher in the RPM range, sacrificing low-end torque for potential top-end gains.
Interpreting Calculator Results
LSA vs. Centerline: While the Lobe Separation Angle is ground into the camshaft and cannot be changed without grinding a new cam, the Intake Centerline changes as you advance or retard the cam installation.
Overlap Calculation: If you see a high overlap number (e.g., >15° at 0.050″), expect a rough idle and low vacuum. Negative overlap numbers usually indicate a stock or towing cam designed for smooth idle and high efficiency.