As far as the 190hp thats to the crank. You are most likely putting down somewhere along the lines of 170 whp. If you are serious about 250 hp whether its to the wheels or crank, your still looking at spending some good money. Build your head. Port, polish, cams, cam gears and valve train. Skunk2 stage 2 cams would work, but you do need to do complete valve train as the stage 2 will ruin your stock valve train. The cam gears and other head work as well is gonna give you a decent gain. Add a good header and exhaust and you are lookin near 230-240. I make 197whp with intake, kamakazi header and 2.5" custom exhaust. All stock head. Turbo though is the way to go.

 

As stated above to jump from 190hp at the crank with an american h22 to 250 at the wheels is no small feat. You're gonna have to heavily modify the internals and get it tuned to handle the power. Also, building the engine is one thing, beating a 300zx with a vg30de is another.

 

dont forget to add that you may have to sleeve the engine, its just those FRM sleeves that come naturally with the h22 engines does playwell when it comes to the piston expanding

and if done right turbo's can spool up at that 2k rpm mark if not a little lower, and they are a lot cheaper then doing a supercharger