Sounds great, but the really neat part is the SpinTron performs these tests at speeds from 500-20,000 rpm.Ī huge benefit of today’s shaft rockers is the increased reliability they offer when compared to an original stud mount rocker arm. This allows Jesel to compare valvetrain stability at various rpm levels, which is an ideal way to prove or disprove new products, theories and materials. The SpinTron records and graphs each new valve trace over the baseline trace. Then the operator (in this case, the folks from Jesel) increase the engine speed to the next rpm level. When using the SpinTron, the first step is to create a baseline valve trace by tracking the valve at a stable engine speed (typically 2,000-3,000 rpm). With the SpinTron, you can precisely identify, document and record crucial characteristics of the valvetrain such as valve bounce, lofting, spring harmonics, and pushrod deflection. You can see the results live (on screen) as the engine spins. The data is transmitted to a computer in the form of a special graph. A SpinTron employs a high-powered AC electric motor to spin the crankshaft and valvetrain of the test engine while a high-tech laser camera (LVTS or “Laser Valve Train Tracking System”) tracks the valve motion and pushrod behavior. Much of Jesel’s research directed toward high-rpm operation is performed in conjunction with SpinTron equipment (basically, a high-tech valvetrain “dyno”). That’s the reason why shaft rockers prove more stable at higher engine speeds. The geometry can be (and regularly is) adjusted with a shaft setup. The reason is the stock stamped rocker can more or less compensate.Ī conventional stud mount roller rocker replacement cannot “fix” the misalignment. This isn’t much of an issue with stock stamped rockers and low valve lifts. Again, using the familiar small block Chevy as the example, the pushrod, the rocker stud, and the valve are not always in line. It turns out that shaft rocker systems also offer a considerable amount of stability at high engine speeds.
Fair enough - the reduction in friction is huge, however that isn’t the end. But as mentioned above, a side benefit was the reduction of friction in the valvetrain. In the beginning, a gain in rocker ratio was a big part of the Jesel plan. That’s essentially how and why Jesel’s line of shaft rockers were born. Instead of physically moving the rocker stud mount, it’s actually easier to start from scratch and build an entirely new rocker arm arrangement such as today’s shaft rocker. But you can’t change the rocker pivot length and correct the rocker geometry unless you move the pivot point. Of course, relocating rocker studs isn’t an easy operation on any engine. less torque to rotate when compared to a stock rocker small block. The idea here was to incorporate big-block rocker arms in the mix (which made perfect sense considering the rat motor’s 1.7:1 rocker ratio).īut something else happened during the R&D: While checking the rotating torque of the engine, the small block fitted with big block rockers consumed 80 ft.-lbs. But when you increase the lift dramatically (as seen in today’s race engines) and simultaneously increase the spring pressure you’re soon faced with another quandary - an increase in friction.Īs it turns out, decades ago, Dan Jesel (the owner of Jesel Valvetrain Innovation) relocated the rocker studs away from the valves on a small block Chevy. This isn’t much of an issue at lower gross valve lifts such as those experienced with stock or mild camshafts (such as those used in production engines). What this all means is the stock small block rocker arm tip more or less scrubs across the tip of the valve as it opens. In comparison, a big block has a pivot length of 1.65-inches). This means the arc it travels in is comparatively small, particularly in contrast to other pushrod engines (Jesel notes that a stock small block Chevy has a rocker pivot length of 1.40-inches. For example, in something like a small block Chevy application, the stock rocker has a relatively short pivot length. The reasons for moving toward a shaft-mount rocker are many-fold.
Where, at one time, it was sufficient to replace something like a stamped rocker with a rollerized example, now we’re dealing with shaft rocker setups complete with a wide range of upgrades and options. When examining today’s crop of roller rockers, it becomes clear that a considerable amount of research and development has occurred over the years - particularly when it comes to race applications. Tons of options are available when it comes to rocker arms for domestic V8 engines.