Mailbag: 5 Things to Check When Swapping to Higher Lift Rockers

I have a 1970 Nova SS with a 11.5:1 compression, 355 cubic-inch small block. It has Sportsman II heads, a COMP Cams hydraulic camshaft (292 degrees advertised duration, .507 inches of lift), and a Holley 750 cfm carburetor on an Edelbrock Victor Jr. intake.

I was thinking about switching from the 1.5 ratio rocker arms to 1.6 ratio rockers. Will this increase performance, or is it a waste of time and money?

Dave F.
Las Vegas, NV

Summit Racing: Switching to 1.6 ratio rocker arms is a very good idea for your engine. You will have .541 inches of total lift with that ratio, and your engine has enough compression for that to make a noticeable difference. Summit Racing has a nice set of 1.6 ratio roller rockers for 3/8-inch studs, as well as a set of 1.6 ratio rockers for 7/16-inch studs.

When you switch to the higher lift rockers, here are some things to check:

• Piston-to-valve clearance (.080 to .100 is good)
• Valve spring bind and retainer-to-seal clearance (.060 mininum)
• Pushrod clearance. A higher rocker ratio usually pushes the pushrod closer to the rocker trunion, which may cause the pushrod to hit the bottom of the guideplate.
• Valve spring retainer-to-rocker clearance. Larger spring retainers may hit the underside of the rocker arm.
• Rocker stud slot interference. Extra clearance may cause the rocker to hit the stud.

This is another in a series of weekly Q&A Mailbag sessions with Summit Racing‘s tech department, in which there are hundreds more. Click here to see them all.