One major difference between modern car engines and older car engines is that modern car engines don't work as hard. In an old V-8 engine, all eight cylinders were firing, no matter if the car was idling or accelerating as fast as it could. Also, all eight cylinders were getting the same amount of fuel, regardless of how much work the engine was doing at the time.
Today's engines have technology that makes them work smarter. Cylinder deactivation is a system that allows some cylinders in an engine shut down when they're not needed, like when the car is idling or cruising. When more power is needed, those cylinders "wake up" and help out. Cylinder deactivation helps engines work more efficiently, since it means the engine only uses the fuel it needs and only extends the effort required for the job at hand.
Variable-valve timing and lift is another technology that helps modern engines work smarter. Without this system, the engine's valves open for the same amount of time and the same distance no matter how hard the engine is working. That wastes fuel. With variable-valve timing and lift, the valve openings are optimized for the type of work the engine is doing. That helps the engine use less fuel, and work smarter.