Comp's High Energy rockers...
Comp's High Energy rockers are a great choice for a Street Stock engine, where stock-style rockers are required, but they weren't designed for the environment in which we put them, and they were simply overmatched.
Comp's Pro Magnum roller rockers are designed to be an effective middle ground between inexpensive aluminum rockers and extremely strong and reliable, but more costly, stainless steel rockers. These rockers sport a list price of $351 and are constructed from chrome-moly steel designed to maximize strength with a minimum of mass. They also have a roller tip. The one deviation with the Pro Magnum rockers is the slightly different 1.52:1 ratio. This small change didn't seem to affect results compared to the 1.50:1 rockers.
On the dyno, the Pro Magnums produced slightly lower numbers than the aluminum rockers. Torque peaked at 401.7 lb-ft while horsepower was 404.1. Average power in the selected range was 386.11 and 366.17, respectively. Looking at the average across the 4,000 to 6,000 sweep, the Pro Magnums were losing approximately two units of both torque and horsepower to the aluminum rockers, which may be attributed to the slightly greater mass.
Comp's Hi-Tech rockers are constructed from ultrastrong stainless steel, which provides race engines with both rigidity and durability. Minimizing power-robbing deflection, which can become a problem with stiff valvesprings at high rpm levels, is the goal here. These are high-end, high-performance rockers, and the list price reflects it at $465. Fortunately, these rockers are rebuildable, so the extra upfront cost can be offset with a longer service life.
Both the High Energy and Magnum...
Both the High Energy and Magnum rockers (shown here) are the pivot-ball type. With this engine's high spring pressures and strong cam, there was simply too much friction, which burned the fulcrum of the rockers. Interestingly, even though not all rockers showed this kind of burn coloring, all the rockers opened up on the lash approximately 0.010 within a few minutes of operation, showing it wasn't a design flaw in the rockers but a bad match between parts and application.
On the dyno, the Hi-Tech rockers were more productive than the Pro Magnums and just south of the aluminum rockers. We got 403.7 lb-ft of peak torque with an average of 387.0. Peak horsepower was 405.2 with an average of 367.06. The average was slightly less than the aluminum rockers. This was surprising, but we feel the valvetrain wasn't being stressed enough for the stainless rockers to shine. As the spring pressures and rpm limit reaches 7,500 and beyond, the Hi-Tech rockers should be able to reduce deflection better than most other designs.
For any true gearhead, these shaft-mounted aluminum rocker arms look like jewelry. Comp says the rocker arms themselves are fully machined and not extruded. There is also an internal oiling system that increases rocker durability by providing pressurized oil from the pushrod cup to the roller-bearing trunnion and to the roller tip. Shaft-mount rockers are gaining popularity in all forms of stock car racing because they provide more stability than stud-mount designs. In addition, the geometry of the stand helps ensure that the rocker tip stays centered over the valve stem at the correct time. Because of the extra machine work required, a shaft-mount rocker system costs significantly more than stud-mount designs-Comp's list price is $1,285-but there isn't a Nextel Cup team today that doesn't use some type of shaft mount system exclusively in its engines, so there must be something to it. The question is, does the benefit extend to the engines typically used by Saturday night racers?
The Pro Magnum rockers were...
The Pro Magnum rockers were the first set we tried with a needle bearing trunnion, which allows much higher spring pressures and solved our problem with rocker death.
The answer is, "It depends." Initially, the results on the dyno were mildly disappointing. Peak torque/horsepower numbers were 401.6 and 405.8, and the averages were 386.05 and 366.28. Those numbers put the results right in line with the Hi-Tech rockers and behind the aluminum and Pro Magnum rockers. But a further inspection showed that the shaft-mount rocker system was just gaining steam versus the competition right when our dyno mule was giving up. Peak horsepower came at 6,100 rpm, but the numbers after peak are quite telling. By the time we got to the end of the test sweep at 6,500 rpm, the aluminum rockers were producing 395.9 hp while the shaft-mount rockers were holding out at 397.3. That's nearly an extra 1.5 hp on the backside of the curve, just 400 rpm past peak. We believe this hints that the shaft-mounted system, like the Hi-Tech, would shine at higher rpm levels and/or with even stiffer springs and a more radical camshaft.
The best conclusion to draw from this test is that you have to match the correct rocker design to the engine package. For our 400-plus horsepower, 6,000-rpm test mule, the best options turned out to be the aluminum and Pro Magnum rockers. The High Energy and Magnum rockers couldn't survive in the harsh valvetrain environment we created, and the Hi-Tech and shaft-mount rocker systems were overkill. Had we used a milder camshaft and springs, the High Energy and Magnum rockers would have worked quite well. The High Energy rockers are an excellent choice when the rule book requires stock-style rockers, and the Magnum rockers are a good performance choice when the budget is tight. Finally, the way the shaft-mount rockers extended the horsepower curve after peak power tells us that this is probably an excellent choice for an all-out race engine, where the engine speed can exceed 7,500 rpm and valve control is an issue. But if your race engine is a more moderate package-like our test mule-spending the extra cash on the shaft-mount system is a bit of a waste. Instead, go with the more moderately priced aluminum or Pro Magnum rockers and use your savings to benefit your racing program elsewhere.