Systematic approach to selecting the right camshaft for your build. Duration, LSA, lift, and overlap explained for street, strip, and race.
Choosing a camshaft is the decision that most changes how an engine behaves, and the specs that describe one are easy to misread. This guide covers what each number means, a comparison tool for putting two grinds side by side, a recommender that works from your combination rather than a catalogue, and a valve spring calculator so the springs match the cam.
Understanding cam specs
Duration at 0.050"
The industry-standard measurement of how many crankshaft degrees the valve is open more than 0.050" lift. This is the only number you can reliably compare between cam brands.
Advertised Duration
Duration measured at a low lift point (varies by manufacturer — 0.004" to 0.006"). NOT comparable between brands. Used for marketing.
Lift
Maximum distance the valve opens, in inches. Determined by: lobe lift × rocker ratio. More lift generally means more airflow potential, but valve springs, geometry, and head port size all limit the useful lift.
Lobe Separation Angle (LSA)
The angle between the intake and exhaust lobe centerlines, measured in camshaft degrees. Affects overlap, idle quality, and power band. Narrow LSA = more overlap, peakier power, rough idle. Wide LSA = less overlap, smoother idle, better vacuum, broader power.
Intake Centerline (ICL)
The crankshaft degree position at which the intake lobe reaches maximum lift (after TDC). Installing a cam advanced or retarded from this spec shifts the power band up or down in RPM.
Overlap
The period in crankshaft degrees when both intake AND exhaust valves are simultaneously open. More overlap = more power potential at high RPM, worse idle, worse low-end torque, lower vacuum. The cam that sounds like a race car at idle has lots of overlap.
Tools on this page
Simple cam timing calculator
Enter duration and lobe separation angle to get intake and exhaust centerlines, overlap, and the valve events in crankshaft degrees. Useful for checking a cam card before you buy, or working out what a grind will actually do in your engine.
Cam profile comparison
Put two cams side by side on duration at 0.050", lift, LSA and overlap, with dual-pattern support so intake and exhaust are compared separately. The specs that matter are rarely the ones printed largest on the box.
Cam selection recommender
Describe the engine and what it is for — displacement, compression, gearing, converter, intended RPM range — and get a duration and LSA range that suits the combination, with the reasoning shown rather than just a number.
Valve spring requirements
Work out the seat and open pressures a given lift and RPM demand, so the spring package matches the cam rather than being guessed at. Under-sprung valvetrains float; over-sprung ones eat lobes.