Koenigsegg produces the most powerful road going 2.0L engine (and it's from 3 cylinders!).
Tiny friendly giant engine - Koenigsegg
How Koenigsegg’s 2.0-Liter No-Camshaft Engine Makes 600 Horsepower
Koenigsegg Gemera's TFG ("Tiny Friendly Giant") 2.0L Twin Turbo I3 engine
Power: 600 HP @ 7500...