i would suggest removing the old camshafts, and replacing them with aftermarket performance camshafts. they can add up to 150 horses alone. but then you must update your fuel pump, your pistons, and the crankshaft. You can also just buy a suoercharger, when can give you more than 600 horsepower if its installed correctly.
The horsepower of a 1985 Ninja 600 is 75 Max
About 38 horsepower for dual-carburetor models of the VLX / VT-600.
i say it would be at least 500 horsepower
108hp
about 120
110 horsepower at 12,500 RPM
600
125 hp
32HP
it is pushing close to 600 horsepower.
horsepower rating 05 gsxr 600:)
600 hp stock