In general, increasing a camshaft's duration typically increases the overlap, unless the intake and exhaust lobe centers are moved apart to compensate.
Increased lift can also be limited by lobe clearance in the cylinder head casting.The .020" number determines how responsive the motor will be and how much low end torque the motor will make.The .050" number is used to estimate where peak power will occur, and the .200" number gives an estimate of the power potential.In some designs the camshaft also drives the distributor and the oil and fuel pumps.Some vehicles may have the power steering pump driven by the camshaft.Where gears are used in cheaper cars, they tend to be made from resilient fibre rather than metal, except in racing engines that have a high maintenance routine.
Fibre gears have a short life span and must be replaced regularly, much like a timing belt.
In a four-stroke engine, the valves are opened only half as often; thus, two full rotations of the crankshaft occur for each rotation of the camshaft.
The timing of the camshaft can be advanced to produce better low RPM torque, or retarded for better high RPM power.
These include: Chilled iron castings: Commonly used in high volume production, chilled iron camshafts have good wear resistance since the chilling process hardens them.
Other elements are added to the iron before casting to make the material more suitable for its application.
An alternative used in the early days of OHC engines was to drive the camshaft(s) via a vertical shaft with bevel gears at each end.