I just did the conversion, heres the old thur hub only and
of coarse I had the y pipe to start with

Quick & Quiet 2 installed

Loto.... it matters not which you get, switchable mufflers or Corsa Quick & Quiet (y pipe thru hub).... NONE can be used above 3000 rpm as they are too restrictive. Still, I know I can run 45 mph and still be under 3000 rpm.. so you can still cruise and be quiet... just not at WOT..

Had Corsa Captains Call on my last boat. All electric and worked great.

NONE can be used above 3000 rpm as they are too restrictive

thanks blown formula!

THAT , i didnt know.

as checkmate454mag suggested , Teague switchables may be how i go. would rather not have to mess with a y-pipe install.

I have Teague's and they work great but they are not as quiet as thru hub. I have run them up to 3500rpm but I think that is pushing it 3000rpm is probably best. 525 blown motor on CMI exhaust.

On a 454 Mag you will hardly notice a difference in performance between open and closed mode.....in my boat with the same engine about 50 rpms. I run the Corsa electric system and am extremely happy with it. Dont go the Merc route, too much weight with all the pumps and lines to install and a lot more complicated too.....

Does anyone know what actually does happen when you go beyond 3000 rpm with the exhaust through the prop on a reasonably stock merc magnum engine?

Probably wouldn't hurt anything. I have seen plenty of stock boats equipped with 454 Mag's and thru-prop exhaust. I don't think Merc would let them go out the door if there was a serious issue. If you are running a lot of overlap with the cam and short risers, however, there would be some risk.

Seems like reversion would be more of a problem at idle anyway, since you don't have the higher velocities and momentum of the intake charge that you get at higher RPM's. Isn't that why you get a choppy idle with long-duration camshafts - partially because of the reversion at low RPM's? I know some of it has to do with the weaker vacuum signal to the carb, but I know I read somewhere that reversion is more of an issue at idle.

Not for sure, but I would assume it is the exhaust pressure overcomes the solenoid holding it open. I believe the "fail" mode is open & the solenoid holds it closed? either open or closed.. the pressure I am sure would overcome the solenoids. It would also probably damage the internal steel (rubber edged flapper) and burn the edges..... Don't think I want to find out though!!