Mailbag: Rocker Arm Ratio…What Does it Mean?

Got questions? 

We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re covering rocker arm ratio and how it affects performance.

S.B. • Atlanta, GA

Q: I want to purchase a set of COMP Cams rocker arms for my 327-powered 1966 Chevy Nova. What is the difference between 1.5- and 1.6-ratio rocker arms? Does an increase in rocker arm ratio improve engine performance?

A: The lobe lift of the camshaft is multiplied by the ratio of the rocker arm to determine the valve lift. For instance, a cam with a .320-inch lobe lift and a 1.5-ratio rocker arm will have .480 inches of valve lift (.320 inches x 1.5 = .480 inches). If you were to install 1.6-ratio rocker arms, the valve lift would increase to .512 inches (.320 inches x 1.6 = .512 inches). The engine will respond as if a slightly larger lift cam had been installed.

In essence, increasing the rocker arm ratio is an easy way to improve the performance of an existing cam.