Rocker Arm Ratio & Net Valve Lift
Lobe lift multiplied by rocker ratio gives gross lift; lash comes off that to give what the valve actually sees.
| Gross valve lift | 0.4770 | in |
| Net valve lift | 0.4530 | in |
| Lash removed | 0.0240 | in |
| at 1.6:1 rocker | ||
| Gross lift | 0.5088 | in |
| Net lift | 0.4848 | in |
| Net lift gained | 0.0318 | in |
- gross valve lift = lobe lift × rocker ratio
- net valve lift = gross lift − valve lash
- Real rockers rarely hit their stamped ratio through the whole sweep — treat this as the theoretical figure.
When you need it
When working valve lift out from a cam card, and when considering a rocker swap to gain lift without changing the camshaft.
Cheap lift, with strings attached
Going from 1.5 to 1.6 rockers on a small block Chevy is worth roughly six or seven percent more lift for the cost of the rockers. It does not change duration, so the engine keeps its character and simply flows a little more at peak.
It also raises valve acceleration and the load the spring sees, and it moves the whole valvetrain closer to every clearance limit you had.
Stamped ratios are nominal
A rocker marked 1.6 rarely delivers exactly 1.6 across the full sweep, and stamped rockers vary more than shaft or roller rockers. Treat the figure here as theoretical. If the lift number genuinely matters, measure it at the valve with a dial indicator.
Re-check everything afterwards
More lift means re-checking coil bind, retainer-to-guide clearance, piston-to-valve clearance and pushrod length. Higher-ratio rockers also change the geometry at the valve tip, so the correct pushrod length is usually not the one you had. A rocker swap is not a bolt-on.