The first Z06 was 385 HP (or about 345 RWHP), the second (cam, pup cat converters, tune etc...) was 405HP (or about 360-365RWHP).
The latest is a dry sump (or so they say) rated at 505HP. (one of the only cars to gain HP in the latest SAE dyno BS). This car puts down about 470 RWHP.
IIRC...