"Can anyone detail what technology breakthroughs got these mileages so high?" I am not speaking of hybrid cars where the technology change is obvious - I am sp

"Can anyone detail what technology breakthroughs got these mileages so high?" I am not speaking of hybrid cars where the technology change is obvious - I am speaking only of pure ICE cars. The "technology", where there is any at all, consists of mostly petty optimizations to the existing ICE model ... engine start/stop at intersections, cylinder deactivation at cruising speeds[1], optimizations to cam timing and making the fuel injection system behave more like a Diesel engine, even when it is a gasoline engine. Again, all petty optimizations that don't represent any interesting technology and I find it laughable to see car advertisements in 2018 for various aspects of the engine/drivetrain. The real gains have been from switching 6-cylinder, 3.x Liter engines out for 4-cylinder 2.x Liter engines and attempting to make up the difference with turbo and super chargers (sometimes both!)[2]. The end result is what you would expect to see in a mature, already optimized, already spec'd technology: very small incremental gains that have large tradeoffs in other areas. These little 2L 4-bangers are loud, they vibrate a lot, and they're going to be very finicky in terms of maintenance when the dual turbo/super chargers get to 8 and 10 years old. I can't wait to never see any of them again. [1] I think this is only applied to 8 cylinder engines which are turned into 4 cylinder engines at highway cruising speeds. [2] ... and generally failing. I hope this "wisdom" is lost to time because we move away from ICE cars entirely, but for anyone still interested: "There's no replacement for displacement".