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If I'm not mistaken the term "brake horsepower" translates to "rear wheel horsepower" as read by a dyno. There are so many variables to this question that only a ball park response is offered:
Brake horsepower by year/model
97-00 C5
290 to 310
01-04 C5
300 to 310
01 Z06
330 to 340
02-04 Z06
345 to 355
05-06 C6
335 to 345
There is a plus or minus factor involved here as there will always be differences in cars and dyno's. But based on many years of real world reports I'd say my numbers are a fair average.