Cam Duration, Overlap & LSA Calculator
Calculate valve timing events, overlap, and cam character from duration at 0.050, lobe separation angle, and advance.
Degrees of advance ground into the cam (0 if installed straight up)
Understanding Cam Specs
A camshaft's character is defined by three key numbers: duration at 0.050" lift, lobe separation angle (LSA), and lift. This calculator focuses on timing — where and how long the valves are open.
Duration at 0.050"
Duration is how many degrees of crankshaft rotation the valve is open. The "at 0.050 inch" measurement is the industry standard because it ignores the sloppy ramp area and measures the "real" opening. More duration = more airflow at high RPM, but less low-end torque and vacuum.
- Under 210°: Mild — stock replacement, towing
- 210–225°: Street — good daily driver cam
- 225–240°: Street/strip — needs supporting mods
- 240–260°: Hot street/race — aggressive
- 260°+: Race only
Lobe Separation Angle (LSA)
LSA is the angle in camshaft degrees between the intake and exhaust lobe centerlines. It determines the engine's personality:
- Tight LSA (106–110°): More overlap, choppier idle, stronger mid-range hit, narrower power band. Less vacuum.
- Moderate LSA (110–114°): Good all-around balance. Most street performance cams live here.
- Wide LSA (114–118°): Less overlap, smoother idle, more vacuum, broader power band. Better for EFI and emissions.
Overlap
Overlap is the period around TDC (exhaust stroke to intake stroke) where both valves are open simultaneously. More overlap helps exhaust scavenging at high RPM but hurts idle quality and low-speed drivability.
Cam Advance
Advancing the cam shifts the entire intake event earlier, moving the torque peak lower in the RPM range. Most performance cams are ground with 2–4° of advance. Retarding shifts power higher. The intake centerline = LSA − advance.
Frequently Asked Questions
What does cam duration mean and how does it affect performance?
Duration is how many crankshaft degrees the valve is open. More duration keeps valves open longer, which flows more air at high RPM but hurts idle quality and low-end torque. Duration at 0.050" lift is the most meaningful spec because it measures the effective opening time. Stock cams are typically 190-210° at 0.050". Performance street cams run 210-230°. Race cams exceed 240°.
What is lobe separation angle (LSA)?
LSA is the angle in camshaft degrees between the intake and exhaust lobe centerlines. Typical range is 106-116°. A tighter LSA (106-110°) increases overlap, creating a rougher idle, more vacuum signal for boost, and a peakier power band. A wider LSA (112-116°) gives a smoother idle, broader power band, and is more streetable.
How does valve overlap affect idle and performance?
Valve overlap is the period when both intake and exhaust valves are open simultaneously. More overlap (from longer duration or tighter LSA) improves scavenging at high RPM but causes exhaust reversion at low RPM, creating a lopey idle and reduced vacuum. Forced induction engines often prefer minimal overlap to prevent boost blowthrough.
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Engine BuildingCam Specs Explained: Duration, Lift, LSA, and Overlap DemystifiedHow to read camshaft specs — what duration, lift, lobe separation angle, and overlap mean, how they affect power, idle, and drivability, and how to choose the right cam for your build.
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