Stud Rockers & High-Performance Engines

When the Chevrolet small-block V8 was introduced in 1955, one of its most highly touted features was its lightweight, high-revving ball and stud stamped steel rocker design. Around 1962, several people proved that claim to be true time and again when they twisted their Duntov-cammed 283s to 7200rpm before each shift. In fact, this same stud rocker setup served performance and racing enthusiasts for years before it became overstressed and the Band-Aids® started to appear.

The first modification made was to install polylocks, which allowed racers to maintain valve lash longer and adjust the hydraulic lifters so that they didn't pump up at high rpm. Those of you who go back a few years probably remember the progression. As more aggressive cam profiles and valve spring pressures increased, press-in studs started pulling out of their bosses. The easy fix was to drill the boss and stud and pin them with a roll pin. Then Chevy came out with screw-in studs that didn't pull out, but their small diameter allowed them to flex too much. The fix was larger screw-in studs made out of stronger alloys. As spring pressures continued to escalate, they too would flex, so stud girdles were invented to tie all of the studs together mimicking the solid shaft-type rockers found on Chevy's sister division engines like Cadillac and Buick.

The History of Aftermarket Shaft Rockers

Dan Jesel, the founder of JESEL Valvetrain Innovation, is credited with inventing the first effective aftermarket shaft rocker arm system. It's an interesting story on how he discovered the real need for shaft rockers. He was building drag racing engines for several customers, and he had two engines: a small-block and big-block Chevy on engine stands ready to be delivered. As was standard procedure, Dan would rotate the engines with a torque wrench to make sure everything was okay (nothing tight or binding). He would check rotating torque at several stages of the build-up. Both engines checked out fine, until the final torque reading was taken with the valvetrain installed and lashed.

The small-block took approximately 80ft.lbs. more torque to rotate than the big-block. That didn't make any sense, because the small-block was less than 302cid and the big-block was more than 427cid. Common sense would tell you that the big-block would have more piston ring drag, and should require more force to rotate.

After taking the small-block apart several times to see if something was amiss, Dan thought about this problem on his several hour tow to the race track. Then he had the "Eureka" moment. The only thing different (other than displacement) between the two engines was the rocker arm pivot length.

That's right, the small-block had a rocker pivot length of about 1.4-inches. The big-block on the other hand had a pivot length of 1.65-inches. What that means was that the big-block rocker tip travels in a much larger arc, which results in minimized "scrubbing" motion across the valve tip. The small-block rocker with the shorter pivot length sweeps across the valve tip, causing increased friction and binding. In production engines with low lift cams and valve spring pressures, the friction is greatly reduced, but when you start putting big loads on the valvetrain from higher lift and higher spring loads, the friction goes up exponentially.

To prove his theory, Dan took a set of small-block cylinder heads and relocated the rocker studs away from the valves, so he could use big-block rockers. The rotating torque test confirmed what he expected – it took 80 ft/lbs less torque to rotate the small-block with big-block rockers. Soon thereafter he was moving studs on all of his customer's small-block engines, when he decided there must be an easier way. There was. He designed a shaft rocker system with stands that bolt to the standard stud bosses, yet relocated the rocker pivot point any distance he desired away from the valves.

That's the crux of the entire stud versus shaft debate – you can't change the rocker pivot length and correct the rocker geometry unless you move the pivot point. So, no stud rocker can perform as well and as reliably as a longer pivot shaft rocker – it's that simple.

The True Advantage of Shaft Rockers

Despite the many advantages we have just listed of shaft rockers versus stud rockers, the real advantage is improved valvetrain geometry. In order to change valvetrain geometry you have to move the rocker's pivot point. With stud rockers that is simply impractical. JESEL relocates the rocker pivot further away from the valve to allow a longer rocker "pivot length". All JESEL shaft rocker systems lower the pivot point as well for a low pivot arc from half to full-valve lift, where spring pressures are the highest. This improved geometry eliminates much of the friction caused by the rocker "scrubbing" across the valve tip. Less friction results in more power and
increased durability!