You can forget your F1 engines, the humble 2 stroke is still king! I believe Kriedler claimed 20hp from their 50cc racers back in the 1980's. The last of the 500cc GP bikes were claiming 200hp and the current 250cc GP bikes are rumoured to have over 100hp. That is 400 horsepower per litre! The best 4 stokes available (F1) make only 300hp/lt or so. A two stroke engine will always be lighter than its 4 stroke equivalent because it doesn't have camshafts or valves etc.
It's a shame no one has made a modern, big capacity 2 stroke engine. I think a 3 litre V6 detuned to around 1000hp would be a good thing on the hills...
Unfortunately in our mundane modern world the two stroke has all but been forgotten.
In reply to the original question, the 13b rotary engine in the early 1980's RX7 race cars claimed 330hp from their peripheral port engines. I believe the engines weigh around 90kg's or so and actual capacity is 1300cc.
Not up to F1 standards I know, but comparing apples with apples, how many mass production engines will make that sort of power for the weight, let alone capacity?