How much horsepower does a v8 engine have?

It depends on year/size and if it is stock or not normally aspirated or force induction, flathead/OHV/sohc/dohc.

Lows

1930's Ford flat heads made as low as 50hp

mid 70's chevy 262 was as low as 110hp

Up to..

Highest HP push rod v8 NA

1964 12.5:1 426 Hemi, under rated at 425(actual HP around 600hp race fuel)factory drag car

2012 corvette Z06- 7L 505hp

Highest NA DOHC

Ferrari 458 - 562hp@9,000rpms

Highest forced induction V8

production car-ssc tuatara 7L TT 1350hp

top fuel dragster supercharged V8- 7,000-8,000hp@ 9,000rpms on 90%nitromethane