stamped steel rocker arm delection

[Chris Hill]

Originally Posted by Alan Roehrich

Pushrod stiffness prevents the pushrod from flexing, and putting its own flex and dynamics into the valvetrain. The rocker cannot even begin to do the damage the pushrod can, the pushrod becomes a spring that flexes and surges, then transfers all of that into the rest of the valvetrain.

Everything you say is correct, but why do you feel the rocker can not become a spring that flexes and surges, then transfers all of that into the rest of the valvetrain?

When I was an engineer for Eaton, the very first thing we did in analysis of a valvetrain is to determine the effective mass at the valve and the valvetrain stiffness. You then determined what the limiting factor speed wise was for the valvetrain.

Either it would be lack of valvespring force or a harmonic issue in the valve train. The harmonic issue was then divided into a mass or stiffness issue.

By far, the most effective way to increase speed is the limit mass of the valvetrain on the valve side.

On a standard pushrod valvetrain, the best place to increase stiffness is at the rockerarm. Per David Vizard's SBC valvetrain book, a SBC rocker has a stiffness of roughly 5,000 lbs/in. I've lost my previous calcs on pushrod stiffness, but I think it's roughly 50,000 lbs/in.