Horsepower isn't the problem it's octane with boost. In the USA you can get e85 which will allow you to run tons of boost and not detonate or knock.
To the guy with the civic comment, yea there's guys running 900hp but it costs a lot as its a lot of power for a 4 cylinder and you'll need all the internal changed. The heads also need to be ported and cams/springs/valves are a requirement. For cost your probably better off with an s65 motor. I'm not sure about the internals of our motors but they should be stronger then a b18 or k20 straight out of the box.