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The advantage of the mechanical roller is that the valve can be opened at a quicker rate, giving you more "area under the curve", or, more effective duration for the same advertised duration. More area under the curve means more air, or potentially better cylinder fill, thus more power. The ramp rate is limited on hydraulics by the "hydraulic intensity" of the lifter. In other words, if you try to move the lifter too quickly, the plunger could collapse or sink during the opening of the valve.
The disadvantage to the mechnical roller is that higher spring rates are required because of the faster lifter/valve action. The higher spring rates are harder on the rest of the valve train, especially the lifters and valve stems and guides. Racing cams are not recommended for the street because of the longer times street engines spend idling or running at low speeds. This is hard on the roller lifter because the roller will overheat because of the high spring pressure. At higher engine speeds there is more oil splashed on the cam and lifters which helps cool the roller. Lifter manufacturers have begun doing things like putting grooves in the lifter body to channel oil to the roller to cool it (cool being a relative term here).
There are mechanical rollers designed for street use though that still have the advantage of faster ramp rates over hydraulics (but not as fast a ramp rate as a racing lobe), and therefore don't require as much spring pressure as a racing cam.
Ladies prefer the gentleman who owns a bowtie especially if its a Camaro
1981 Camaro Z28 - Zed the Canadian Wonder Car eh!
1983 Camaro Z28 - 6,890 miles original unrestored
Edited Feb 21, 2007 at 11:03 pm