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Light and small displacement 4 cylinder engines with variable valve timing where a response to the need to increase the brand fleet MPG averages. Reliable turbos needed time for engineers to create the turbo controllers, some combining variable valve timing. There has also been the nagging drag of many drivers needing auto transmissions, which compound the fuel economy issue, drastically! European cars are more likely to have a clutch, if purchased in Europe! CVT has become the go-to for many auto manufacturers in the USA (forced by automatic transmission "requirement") trying to squeeze fuel economy from an ICE. The weird 3 clinder CVT in the new Bronco is a prime example there.

These more recent developments have created some pretty efficient and powerful vehicles though. My son has an '02 Civic with a remarkably efficient and reliable 1.7L 16 valve 4 cylinder engine. Turbos really make a difference though, especially if you can pair it with a clutch. I was amazed when I stumbled into a late model Jetta from a lease return with a third pedal, and an amazing 1.4 liter turbo charged gasser. Lots of horsepower for such a little engine (nearly 150), but the remarkable thing is that it will deliver over 45mpg on the highway too. I get 43-44mpg combined, mostly city.

I was into turbo diesel until deiselgate destroyed the tunes, pre-DEF. It became impossible to override the injection retarding method for eliminating NOx. Before that, you could squeeze 50mpg out of them and making real horsepower. Gone. It was all about Oxides of Nitrogen (NOx). Personally, I prefer to get the additional 12-15 miles on each gallon, thereby emitting far less CO2, and they were also way more powerful while still delivering the MPG! Some cars and mega trucks get 12-15!