The drawback is that higher compression ratios require higher octane fuels. Nissan claims to have solved this by some kind of intelligent feedback system that allows them to control compression ratios on the fly. Presumably the compromise there is that it will require more moving parts, be expensive, and may come with issues of its own.
Variability in something like a combustion chamber is a cool idea, so is variability in the angle of turbo vanes. The issue is how you do it, affordably, and in a way that lasts the way that consumers expect from their cars.
The obvious precedent for variable-pitch blades are variable-pitch propellers on aircraft and helicopters. I don't want to say it's a solved problem for turbos, but there is almost a century's worth of prior art on the topic. That's one of those things that (in hindsight) really makes you wonder what took so long to think up.
Because it has to be cheap and reliable at 1000*C for 200,000 miles over 10 years while constantly accelerating to 280,000RPM and decelerating with no oil or cooling air circulating when the car is stopped. https://garrett.honeywell.com/products/how-a-turbo-works/
Variable geometry turbos are a thing, and have been for some time. The larger trucks and semis use this technology. Typically they are hydraulically controlled.
That's a challenge, but the thing is a turbo deals with blazing hot exhaust gasses just out of the manifold. A prop is still a marvel of engineering, but it doesn't need to be made of boron carbide to not melt.
A better comparison would be variable pitch vanes on jet turbines.
Right, I figured this must actually be an anti-knocking technology. My point was just that the quote implied power and economy are optimized by taking the compression ratio in different directions, which is wrong.
1) lets the engine have high compression AND a turbo. Typically a turbo is run with lower compression, because even today nobody can make an engine run 14:1 with a turbo. Speculating, when you floor it the compression might drop to 8:1 and the turbo kicks in; then when you highway cruise, it runs 14:1 for efficiency.
2) lets the little engine still hit big torque numbers at low speeds. This is most likely if the engine is variable stroke, as longer strokes improve low speed torque.
Ahhhh, those both make a lot of sense. This could be a nice feature on higher-end cars that try to use smaller engines, with more turbos, for the sake of fuel and emissions then?
Maybe the trick would be to have two crank shafts, with two pistons per "cylinder" (or combustion space), and run them slightly out of phase with each other to vary the compression....
Variability in something like a combustion chamber is a cool idea, so is variability in the angle of turbo vanes. The issue is how you do it, affordably, and in a way that lasts the way that consumers expect from their cars.