Inputs
Results
Overlap = (intake opening + exhaust closing) / 2 reported as degrees of crank past TDC. Smaller LSA → more overlap, more low-end torque loss, more top-end breathing.
What this calculator actually solves
Most cam calculators just hand you back the duration you typed in. The interesting question is: what does that duration buy you in overlap, and how does that interact with the intake you actually installed? This calculator takes the @.050" duration plus the lobe separation angle and shows you an overlap estimate plus a coarse RPM-band characterization. It's not a dyno prediction, but it lets you sanity-check whether the cam card and the intake setup are talking to each other.
Where the cam card lists intake closing in degrees after BDC, the calculator converts the value into an effective dynamic compression-ratio adjustment flag. Early intake closing (e.g. 38° ABDC) raises effective CR and broadens the power band; very late intake closing (60°+) drops effective CR at low RPM and tightens the band upward.
Who this is for
Engine builders matching a cam to an existing intake who don't want to re-curve the intake just because the cam card says 224° at .050".
Race engine builders checking whether a tighter LSA for more overlap is actually what the rules class wants, or whether they're giving up too much torque for a small top-end gain.
Restoration and street-rodders who bought a cam on the strength of a magazine dyno and now want to know whether it'll be a torque or a dog on their specific combo.
How to read the results
If "Estimated overlap" comes out under 5° on a hydraulic flat-tappet build, you have a very street-friendly cam — low RPM tractability, mild lope. If it's above 30° on a hydraulic flat-tappet, expect a noticeable idle quality drop and a stall converter if it's an automatic.
The IVC reading is the most useful single number. An IVC well past 50° ABDC means the cam is making power high (4500+ RPM) and will feel dead below 2500 RPM. An IVC around 30–40° ABDC keeps the bottom-end alive and trades top-end power for usable torque.
Limitations
This calculator assumes advertised duration follows the standard SAE J1313 convention (1.27 mm / .050" lash). Many offshore cams do not. If your cam card lists "duration" without a lift value, the number is probably .004" tappet-lift, not .050" — and the .050" figure will be 25–35° lower.
Overlap is an estimate. Real overlap depends on ramp rate, valve spring pressure at low lift, and intake tract tuning — not just LSA.
This calculator does not simulate variable-valve-timing (VVT) or cam phasing. On engines with VVT, the LSA you entered represents the center position only.
Frequently Asked Questions
What LSA should I choose for a street 350?
For a hydraulic flat-tappet small-block with stock converter and 3.08 rear gears, 110–114° LSA is the sweet spot. Tighter than 108° and you'll lose idle quality; looser than 116° and you're not getting any benefit from the cam upgrade.
Why does advertised duration matter if .050" is what people use?
It doesn't, for comparing cams. Advertised duration is a marketing number that includes the slow ramp region (below .050"). When you're comparing cams, always use the .050" number — that's where the cam is actually doing useful work.
My cam card says "duration 270°" with no lift qualifier. Is that .050"?
Almost certainly not — that's most likely .004" tappet lift, the cheap-and-easy-to-measure number. The .050" number on the same cam will be 220–235°. Use the .050" figure for everything in this calculator.
About this tool
What this tool is for: Cam Duration & Lobe Separation Angle Calculator is a workbench reference for working mechanics, machinists, restoration shops, and serious hobbyists. It is built because the usual online calculators skip the friction loss, the sign convention, the unit conversion, or the engineering code that actually matters on the job.
Purpose and scope
Cam duration @ .050" plus LSA overlap trend. Useful for choosing a camshaft for an intended engine use, not for predicting off-idle drivability — that requires VE and intake-runner modeling alongside.
How to use the body of this page
The sections above this footer — “What this calculator solves,” “Who this is for,” “How to read the results,” and “Limitations” — describe in detail what the formula does, why a tech would use it, how to interpret the number, and where the model is wrong. The FAQ block answers the three or four questions most asked about this specific tool. Together they make up the “About” content for this page; you do not need to look elsewhere.
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