I mess with turbo engines... ethanol and E85 are a godsend.
More boost and more timing without detonation.
You guys just are not carrying enough combustion pressure.
As to diesel... buddy of mine has a 1st gen dodge cummins with 3.07 gears and a 5 speed. Gets 28-30 mpg average on the hiway @ the speed limit with a best of 32.
I will take that kind of fuel economy with the ability to work it nice and hard.
Jim