Next came the overhead cam where the cam operated a lifter which directly operated the valve. Up until the mid-1980s most vehicles used two valves per cylinder, an intake valve and an exhaust valve. Beginning in the last half of the 80s, in order to gain efficiency and lower emissions, car makers began adding cams and valves. Now four valves per cylinder, two exhaust and two intake valves, with two camshafts per head is a common design. In order to further increase efficiency and performance, variable valve timing was introduced. Variable valve timing allows the valves to open or close with different timing to match different conditions of speed and engine load.
The materials that engines are made with have improved greatly also. Piston rings used to cause a taper in the top of the cylinder bore as material was worn away from the cylinder wall. Today this condition is rarely seen. Toyota uses a porcelain lined cylinder on some of its models. This eliminates hot spots, reduces wear and allows for better thermal efficiency.