anyone know how the exhaust exits in a cmi exhaust in relation to a stainless marine bbc? is it general, or are where the tips all custom. it is a bravo application. the cmis are 4.5inch tips, and the stainless marines are 5in. also, does anyone know where to find switchable mufflers or external mufflers for 5inch exhaust? thanks

also, what is the purpose of a hinged "flapper" inside of the tip? does it just keep water from getting in the tip when you unload or reverse? it looks like the exhaust would blow them upwards at any rpms, do they muffle the sound at all at lower rpms, or could you at least argue they work the slightest way like mufflers? thanks

They don't muffle anything. They are to prevent water from coming back up the exhaust. They may help if you come off plain too fast or back up too fast, but I doubt it. With the engine running, they are pretty much open and the exhaust pressure will keep water out. What they will do is keep water from coming in when the engine is off, like if you if floating or docked and a big wave hits the back of your boat.