Why Can't These Parts Get Along?
The challenge in using race-bred valvetrain parts on the street boils down to the individual parts being at odds with each other. To make maximum power, a roller camshaft snaps the valves open and closed very quickly. This places immense side-loading force on the lifters, literally forcing them up by squeezing them against their bores. In addition, the valvespring pressure is very high in order to control the valves as the cam cycles them. If the springs aren't matched to the cam profile and the maximum rpm of the engine, the valves can actually bounce when they close, and the lifters won't stay on the cam lobes. This is bad for power, and it can be catastrophic for the engine. Even with the latest technology, a huge race cam on the street will eventually kill a set of lifters. In fact, Kurt Urban recommends we replace the lifters in this engine after 5,000 street miles or immediately if we find that the valve lash loosens up. While we're at it, the valvesprings should be checked each year, and replacing them before seeing hard racing use is a wise choice. How big is too big? It's best to work with a knowledgeable team like the folks at COMP Cams to make that determination for your specific application.
Hydraulic Versus Solid
Most engine builders opt for more moderate cam specs on an engine that will spend most of its life on the street. Sure, you'll give up some power, but you have to weigh the pleasure of hassle-free street driving with maximum horsepower at wide-open throttle. Just as important as the cam specs is the basic type. A roller camshaft will make more power because of the steep ramps that are possible, but should you use a solid roller or hydraulic? A long time ago, a roller lifter cam meant constantly checking the valve lash-the clearance between the rocker and the valve tip. In a solid lifter setup today, that's still true. The advantage of a solid lifter, in addition to maximum power, is that the valve lash is a great canary in the coal mine. If you find more clearance, something is wearing or broken, and you need to inspect the rocker, rocker mount, valve tip, and lifter. If you suddenly have less clearance, you probably have a valve that's mushrooming, and it's time to pull the heads. Hydraulic lifters absorb some of the beating within the valvetrain, especially the bearings in the roller lifters themselves. They also alleviate having to periodically check and adjust the valve lash. Matt Summerfield at COMP really would have preferred that we use a hydraulic roller cam with 266/274 degrees of duration at .050 and .646-/.646-inch lift for this engine. This would have greatly extended the life expectancy of the lifters and would make the valvetrain virtually maintenance free.