exhaust question 350 chevy/omc outdrive

[sweat equity]

good morning, I am repowering my 26' aquasport. Would like to exhaust through transom below waterline. Is this a bad idea? Do I need some kind of check valves or flappers? thanks for any advice you can offer.

 

[Bondo]

Re: exhaust question 350 chevy/omc outdrive

Ayuh,... I wouldn't do it without shutter/ flappers...

 

[wire2]

Re: exhaust question 350 chevy/omc outdrive

Which OMC? Stringer or Cobra?