Reply #5: the only thing conceptual about this is the variable compression ratio. There is nothing conceptual [View All]

about supercharging or turbocharging producing more power from the same cu in. and allowing downsizing. The result is you can get equal power from a smaller mill and mileage equal to or better than the larger naturally aspirated engine.

with ethanol (E85) having an octane rating of 113 you can use more boost and higher effective compression - and thus more power per cu in.

GM knows this but doesn't want to make the effort - probably because there are so few E85 pumps available. Still, I think they could offer it as an optional engine on FFVs. The fuel sensor could set timing and boost so you could optimize for the octane.

Burning a fuel under compression means the octane rating is very important. I'd take a higher octane fuel any day over a lesser one IF I had an engine that can take advantage of it.