The Evolution of the Camshaft II
In the Evolution of the Camshaft I, we discussed how camshafts work and how they fit into the valve train. This week, we’ll be discussing advancements in camshaft technology which have made a significant impact in the way our engines gulp air.
During your daily commute you may have seen stickers and tags on other vehicles, like, VVTLI, VTEC and VVL. Each of these acronyms refer to different types of Variable Valve Lift (VVL) or Valve Timing and Lift Technology. We have already established that the camshafts determine how long valves are open (duration) and how deep the valves open (lift). We have concluded, that the more lift and duration your camshaft has the more horse power it can potentially create, however, additional lift and duration negatively impacts fuel economy and drivability. Prior to the development of Variable Valve Lift technology, a car enthusiast was forced either accept the additional expenses and reductions in comfort to achieve his desired power levels or forget about up-rated camshaft in favour of a more practical daily driver. The Variable Valve Lift technology allows for the best of both worlds.
In these systems, the camshaft is designed with more than one lobe per cylinder, so at lower RPM while the driver is going about his day to day activities he maintains a smooth and comfortable ride and good fuel consumption and when the need for performance arises the driver can rev the car higher and the high performance lobe is engaged it transforms the car into a totally different machine.
Toyota, Mitsubishi, Honda and Nissan all have versions of this system. However, they all operate in a similar manner. Because of these similarities, I will focus on the VTEC system from Honda. In this particular system, each pair of valves has three cam lobes, two that operate the valves at low-rpm, and a third which is larger and takes over at high rpm. During low-rpm operation, the two rocker arms riding the low-rpm lobes push directly on the top of the valves. At higher rpm usually between (4500-6000) rpm, the Engine Control Unit (ECU) sends a signal to an oil control valve that allows oil pressure to flow into the low-rpm rocker arms. The third high rpm rocker arm sits between the two low-rpm arms. When the oil pressure arrives, two steel pins pop from the sides of the low-rpm rocker arms and slide into sockets in the high-rpm arm, and the valves start following the larger cam lobe. At this point the engine transforms, there is a rush of power more air and fuel rushes into the engine, this change is often audible both inside of the car and outside to passersby. In enthusiast circles in Barbados we call this, “going pun lift”.
Max Boost!!! is a weekly column written by Dwayne Browne
For over 10 years, Dwayne Browne has gained a wealth of knowledge in engine modifications and performance enhancements, through his many project car experiences.
