Over the past 10 years or so there are two main things: 1. various technologies to vary cam timing and lift, which allows you to keep the engine efficient over

Over the past 10 years or so there are two main things: 1. various technologies to vary cam timing and lift, which allows you to keep the engine efficient over a wider range of rpms. Forms of this have been around a long time but they are become more widespread and more capable. 2. direct injection - where some or all of the fuel injectors inject directly into the cyclinder, rather than into the intake manifold just before the cylinder. Because the fuel can be added just when you want it to ignite, you can leverage higher compression ratios and/or turbo chargers without pre-ignition on top of this there have been some small improvements in tire CRR, aerodynamics, materials. But a lot of the use of lightweight materials seems to coincide with also making the cars bigger. They certainly haven't gotten lighter overall! If cars had stayed the same dimensions since the 1980s, the fuel economy savings would seen WAY more amazing.