Will it be a good idea to straight-pipe a V8 engine block?

Straight open pipes will only work well on wide open throttle. You need some back pressure to work effectivly at low rpm. Some damage may happen due to the fact your heads and valves will cool faster then normal You will be better off with hi flo mufflers to provide the back pressure for normal driving at low rpm. Not much gain with open pipes unless its just used to go down a drag track. Just use a exhaust cut out for open pipes at race time.