Don Terrill’s Speed-Talk

Does anyone happen to know the spherical radius of ye olde generique small block Chevy rocker balls?

Failing that, any ideas on a way to measure one? There's not a whole lot of sphere left on the finished parts...

Measure the radius of the pivot ball with a radius gage. Whatever that is, that is the radius of the circle the rocker is pivoting around. If you use a radius from a standard machinist radius set, like a Starrett or Lufkin set, you can lay the half ball in the gage and measure to the bottom/top of the radius gage cutout, and it will tell you how much distance you should add to the flat side of the ball part to give you the center of rotation. This is hard for me to explain, but maybe you can see what of visualize what I'm saying. Then imagine a line intersecting the valve pad and the distance you had to add to the top of the pivot ball. Then, with your valve at half lift and the cam at half lift, see what you need to do to make your imaginary line PARALLEL to the top of the spring retainer. Adjust the pushrod length to see if that looks like it's possible to make all of those things work without hitting the valve stem corner of running off the end of the rocker arm. If either of those things happen, adjust pushrod length to get the best compromise.

If all that sounds too complicated, just use a pushrod length that puts the outward edge of the valve stem as close to the outward end of the rocker pad as you can. That should give about the greatest rocker ratio you can get.

MOST IMPORTANT is to check the rocker-to-stud clearance at the bottom of the pivot ball. If there is any bottoming out in either direction, you will break things. ALSO, you may need long slot rocker arms to achieve your geometry goals.

Some years ago, I used long slot stamped rockers, home made 3/8" stud girdles, and .500 lift street roller cam setup, with all the stuff fitting under stock stamped steel rocker covers. (CC 244@.050" Street roller.) Made a good sleeper. No one figured out why a street 302 ran so good.

Sorry for all the typos. That's what I get for hurrying earlier.