Camshaft Duration Calculator

Cam specs from target RPM range and application.

Peak power RPM

Rocker arm ratio

Lobe separation angle (°)

Cam advance (°)

Application (0-2)

Tab to move between fields

Intake dur. @0.050" (°)

328

Exhaust dur. @0.050" (°)

336

Intake advertised (°)374

Exhaust advertised (°)382

Intake valve lift (in)0.6

Exhaust valve lift (in)0.58

Valve overlap (°)220

Est. idle vacuum (inHg)2

Intake Centerline108

Min Idle Rpm2,210

Power Band Start3,000

Power Band End6,000

How to Use This Calculator

How the result changes with Peak power RPM

Peak power RPM: Target RPM for peak horsepower. Street: 4500-5500, street/strip: 5500-6500, race: 6500+.
Rocker arm ratio: Rocker arm ratio multiplies lobe lift. Stock SBC: 1.5, aftermarket: 1.6-1.8.
Lobe separation angle (°): LSA in degrees. Tight (106-110): peaky power. Wide (112-116): broad torque, smooth idle.
Cam advance (°): Degrees of advance ground into the cam (positive = advanced, shifts torque lower in RPM).
Application (0-2): 0 = mild street/tow, 1 = street/strip performance, 2 = dedicated race.

Intake dur. @0.050" (°): Intake lobe duration measured at 0.050" tappet lift — the industry standard cam comparison metric.
Exhaust dur. @0.050" (°): Exhaust lobe duration at 0.050" tappet lift.
Intake advertised (°): Seat-to-seat (advertised) intake duration.
Exhaust advertised (°): Seat-to-seat (advertised) exhaust duration.
Intake valve lift (in): Maximum intake valve lift = lobe lift × rocker ratio.
Exhaust valve lift (in): Maximum exhaust valve lift.
Valve overlap (°): Crank degrees where both intake and exhaust valves are open simultaneously.
Est. idle vacuum (inHg): Estimated intake manifold vacuum at idle — lower = rougher idle, may need converter.

Identify Input Parameters
4 parameters
Peak power RPM = 5500, Rocker arm ratio = 1.5, Lobe separation angle (°) = 112, Cam advance (°) = 4 = 5 input(s) provided
Calculate Intake dur. @0.050
Intake dur. @0.050 = round((peakPowerRpm / 30) + 140 + durationBonus)
328 = 328
Calculate Exhaust dur. @0.050
Exhaust dur. @0.050 = intakeDuration050 + exhaustExtra
336 = 336
Calculate Intake advertised
Intake advertised = intakeDuration050 + advertOffset
374 = 374
Calculate Exhaust advertised
Exhaust advertised = exhaustDuration050 + advertOffset
382 = 382