In the initial testing of our Mauler 440 engine project, we had a chance to see how close our selection of parts came to meeting the stout objectives we originally set. The one thing that stood out from that test session was that our combination was overwhelming the capabilities of the flat-tappet hydraulic camshaft we were running. In the quest for the ultimate in fast-acting valve motion, we started with the quickest of the quick .904-inch flat-tappet profiles, and then goosed the rate to an unheard of speed with a set of 1.7:1-ratio rocker arms. As flat-tappet hydraulics go, it was intense, reaching .600-inch lift with a short 231 degrees of duration at .050-inch lift. As our testing showed, the fast rate had the potential to make the number, but the effort was hampered by the ability of the lifter's hydraulic mechanism to cope with such aggressive action. The simple solution was to move to a solid street roller.
When very quick valve action is the goal, a solid roller is the conventional choice. Fast valve action is precisely what this type of camshaft configuration is created for, and we had no doubt that the setup would work. Being a solid design, any question of hydraulic instability would be moot, since there is no fluid mechanism to foul. The roller allows much higher-rate valvesprings to be run without the risk of wiping the cam or lifter face due to overloading. With the flat tappet used in the previous test, we had pushed the spring loads to the limits of what we'd gamble with-at 377 pounds of pressure over the nose, it was a gamble. With a roller cam, spring loads in the range we'd need for control would not be an issue. We could have made another play at finding a magic spring combo for our hydraulic flat tappet, but by changing to the roller, all of the problems with operating the valves in our combo would be solved in one swipe.
The CamWe were still aiming our effort for street use, so our lobe shopping was focused on the Xtreme Street Roller lobes in Competition Cam's line-up. Our hydraulic flat tappet measured 231-degrees duration at .050-inch lift. Since we were moving to a solid profile, we needed to go with a cam larger in duration, as measured at .050-inch tappet rise to make up for some of the loss of duration at the valve created by the lash. A rule of thumb is, a solid cam with 8-10 degrees more duration than the flat tappet will approximate the .050-inch duration number of a hydraulic, once the lash is taken into account. With a little greed in our minds, we settled on just a little more than that, selecting lobe numbers 4874/4875, stretching the duration to 242 degrees on the intake, and 248 degrees on the exhaust. These street roller lobes would blow away the lift we were able to achieve with the flat-tappet cam, opening the valves to a full .646 inch on the intake, and .653 inch on the exhaust, when combined with our aggressive 1.7:1 rocker ratio. The high lift would also play well with the high-lift airflow capabilities of our Indy CNC 295 EZ heads. With all the extra air up for grabs by just tipping the valves open a little further, it makes sense to tap into the potential. As with our hydraulic grind, we had the camshaft ground on a wider 112-degree lobe separation angle, a move that will help bleed some low-rpm cylinder pressure with our high-static compression ratio, and help to improve idle quality and vacuum.