ANDRA Fastlane 20 - Page 10

10 fastlane techtorque MAKING THE MOST OF MODERN FLAT TAPPET CAMSHAFTS Story and Photos by Wayne Scraba IS THE FLAT TAPPET CAMSHAFT A DINOSAUR? Roller lifter cams are today’s norm. But flat tappet cams still see considerable use. Up until a few short years ago, NASCAR mandated flat tappet cams on their Cup Cars. In NHRA Stock Eliminator, there are still plenty of good old- fashioned flat tappets in use. The same applies to countless hot rods, vintage musclecars, and street machines. Flat tappet cams that were once considered state of the art are no longer. What we’re seeing today are cams with more radical opening and closing rates similar to the “square nose” cams developed years ago for NHRA Stock Eliminator racers (see the accompanying photos). These cam profiles place more area under the curve, which makes for improved cylinder filling as well as enhanced exhaust pumping. Modern valve spring and valvetrain parts allow the use of radical flat tappet cams. A good example is the beehive-style spring. The beehive configuration allows the valvetrain to handle more RPM and more aggressive cam profiles. The spring’s oval/multi-arc wire shape places the maximum area of the wire at the point of highest stress. This allows the spring to handle valvetrain loads more efficiently and provides better heat dissipation for longer life. Beehive valve springs are also lighter and use a smaller, lighter retainer than traditional springs. Of course, flat tappet cams do limit the spring pressure you can safely use, particularly in comparison to a solid roller. Spring rates for flat tappet cams vary by application. For example, the seat pressure on a hydraulic grind will be less than 135 pounds with an open pressure of 350 pounds maximum. A solid cam can have a seat pressure less than 160 pounds and an open pressure of 385 pou ̸)A͡ɽ́ɔѡȁЁѡЁ́չɝ)ȁ́ѡхɐ͵) ͡ɽ݅́Լصѕȁ)%Ё݅́ՙЁȁЁ䁍)ԁձՙѡ%ѽéݽɱ)Ёɼե́ݥ٥͔ԁѼ͔)ѡаѥЁ͡ɽԁЁ݅