Enter your camshaft specs — intake/exhaust duration at 0.050", advertised durations, Lobe Separation Angle, cam advance, and valve lift — and this Camshaft Duration Calculator works out your valve overlap and exact intake/exhaust opening and closing events.
Valve Overlap
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Intake Opening
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Intake Closing
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Exhaust Opening
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Exhaust Closing
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Intake Centerline
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Valve overlap is the period when both intake and exhaust valves are open simultaneously near top dead center. It helps scavenge exhaust gases and can improve cylinder filling, but too much overlap can cause rough idle and poor vacuum.
LSA determines the relationship between intake and exhaust events. Tighter LSA (108-110°) increases overlap and torque but reduces idle quality. Wider LSA (114-116°) improves idle and vacuum but may reduce peak torque.
Advertised duration measures from seat-to-seat at very low lift (typically 0.004-0.020"). Duration at 0.050" is measured at 0.050" lift and is more consistent between manufacturers for comparing camshafts.
Advancing the cam (installing it ahead of straight up timing) opens and closes all valve events earlier. This typically improves low-end torque but may hurt high RPM power. Retarding has the opposite effect.
Forced induction engines often benefit from less valve overlap to prevent boost pressure from escaping through the exhaust. Wider LSA and different timing strategies help optimize scavenging without losing boost pressure.
Longer duration moves the power band higher in RPM but reduces low-end torque and idle quality. Choose duration based on your intended RPM range, vehicle weight, transmission type, and desired characteristics.
Higher lift generally improves airflow but requires stronger valve springs and may limit RPM. Most street engines work well with 0.450-0.550" lift, while race engines may use 0.600-0.700" or more with appropriate valve train components.