The NASCAR Technical Institute in Mooresville, North Carolina, was the location for the te
Because we were striving for consistency from one dyno pull to the next, the engine wasn't tuned for maximum power. Timing was set at 38 degrees with the advance locked out. The Holley carburetor was set up with No. 70 jets at all four corners, and 7 quarts of Royal Purple synthetic racing oil was used for lubrication. Those factors did not change throughout the tests. When the pulls were made, lead instructor Doug Wolfe made sure that the water and oil temperatures were as consistent as possible. Our targets for the beginning of each pull were 190 degrees F for the oil and 180 for the water.
Comp's High Energy rockers can be best described as high-quality stock replacement rockers. These stamped steel units are designed to be used with stock or High Energy camshafts. They are very popular among Street Stock racers because they look like stock pieces but are manufactured to tighter tolerances and can be purchased with a higher ratio than the stock rockers for some engines. They are also the least expensive rockers we tried, with a list price of $141 for a set.
In terms of technology, the Magnum rockers are definitely a step up from the High Energy rockers. Magnum rockers are constructed from chrome-moly steel and feature roller tips for reduced friction. With a list price of $212 for 16, they are still quite a bargain. Both the High Energy and Magnum rockers swivel on a pivot ball system.
As part of this experiment, we wanted to test how much rocker stud stability played into t
We knew from the start that both of these rockers wouldn't be the best choices, given the radical camshaft and stiff valvesprings we would be using. Pivot ball rockers have been used for years in OEM and lower division racing classes with great success, but our engine combination was just too much. The problem was that the pivot ball that locates the rocker pivot point was not as efficient at reducing friction as rockers with a bearing trunnion. On the dyno, the high spring pressures combined with the large amount of lobe lift burned up the fulcrum area of the rockers. We had to kill both runs quite quickly, and as a result, we have very little information regarding these rockers. We got one pull to 5,000 rpm for the High Energy rockers and didn't make a pull for the Magnums.
The lesson here? There is a good reason that valvetrain component manufacturers and engine builders try to steer you to the high-end stuff-and it usually isn't because they just want you to spend all your money. Extended operation at high rpm levels is incredibly hard on your valvetrain, and it is critical to get the right parts for the right job. The pivot ball system just isn't designed to be used in the high-rpm, high-lift application to which we subjected these rockers. We want to stress that neither the High Energy nor the Magnum rockers are poor designs. With a milder camshaft, we've seen them operate perfectly and make good power. This was simply a situation of poor component matching. Learn from it.
By comparison, the 7/16 screw-in ARP stud showed only 0.0015 inch of movement with the alu
The next step up in terms of cost is Comp's aluminum roller rockers. At this point, all of the rockers tested used 71/416 screw-in rocker studs. The aluminum rockers are also marked to transition to needle-bearing trunnions, meaning they are rated for spring loads with up to 350 pounds of open pressure. The list price for the aluminum rockers jumps up quite a bit, but they are still the cheapest bearing trunnion option at $343 for a set.
On the dyno, the aluminum rockers performed flawlessly. Peak torque was 404.2 lb-ft at 4,600 rpm, and horsepower maxed out at 406.1 at 6,000 rpm. For all tests, peak numbers stayed very close to those two points. Only horsepower varied by 100 rpm. We also tracked average torque and horsepower across a range of 4,000 to 6,000 rpm to simulate on-track operating rpm range. Again, the aluminum rockers displayed the best numbers. Average torque was 388.33 while horsepower was 368.31.
The advantage almost certainly comes from the fact that the aluminum reduces the overall weight of the rocker, which cuts down on the inertial forces in the valvetrain. Aluminum's drawback is its tendency to fatigue, unlike steel. But it isn't usually an issue in circle track racing if the engine is regularly rebuilt. Your power level and on-track rpm range will determine the duty cycle of the rockers, and the manufacturer's tech department can normally help you with determining when the rockers should be cycled out. The improvement over the other rockers is slight, as you will see in the next tests, but it was measurable.