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Rocker ratio and valve lift calculator

Your cam card lists lobe lift, or valve lift at a specific rocker ratio. This shows the lift your valves will actually see with the rockers you're running, and what other ratios would give you.

Enter your numbers
Cam and rockers
If your card only lists valve lift, divide it by the ratio it was quoted at.
0 for hydraulic lifters.

Lift at the valve

–
Lobe lift × rocker ratio, minus lash.
Gross lift (no lash)
–
Change from 1.5 ratio
–
Rocker ratioNet valve lift

More lift has a price

Before stepping up in ratio, check valve spring coil bind, retainer-to-seal clearance, piston-to-valve clearance and pushrod geometry. Each one gets tighter as lift goes up.

How valve lift is calculated

Valve lift = lobe lift × rocker ratio − valve lash

The rocker arm is a lever. A 1.5:1 rocker moves the valve 1.5 times as far as the pushrod moves it. Solid-lifter cams run with lash (a small gap), which the valvetrain has to take up before the valve starts to move, so it comes off the total. Hydraulic lifters run without lash.

Reading a cam card

Cam cards often list "valve lift" already multiplied by a stock ratio, typically 1.5 for a small-block Chevy or 1.7 for many Fords and LS engines. Divide that number by the listed ratio to get lobe lift, then use the ratio you're really running.

Frequently asked questions

Why does my cam card list lobe lift instead of actual valve lift?

Lobe lift is a property of the cam itself, independent of whatever rocker arm ends up running on it — actual valve lift depends on the rocker ratio too, so the cam card's number is only the starting half of the real answer.

Would switching to a higher ratio rocker give me more power?

It increases valve lift and can improve flow at a given cam, but it also increases valvetrain stress and can affect valve-to-piston clearance — it's a legitimate tuning option, not automatically an upgrade, and should be checked against your specific engine's clearances.

Why does valve lash get subtracted in the formula?

Lash is the intentional small gap in the valvetrain that's taken up before the valve actually starts to move, so it reduces the lift the valve actually sees compared to the raw lobe-lift-times-ratio number — accounting for it gives a more accurate real-world lift figure.

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