Here are some pictures of the external exhaust that I did to my 38 Cigarette running 1100hp blower motors. After the "turn-downs" were added, I was never stopped again. They work, and are NOT a restriction to the exhaust when up on plane. Additionally, the exhaust is between the drives so when running the sound is "held" in that area and doesn't radiate out to the sides of the boat. Also they point downward, not backward which also helps. Note that the pipes are approx. 6" under water at an idle state. I hope this is useful.

Nice application
.............but why did you fabricate the outside pipes to go all the way to the center?
I have similiar, application( 47 fountain w big power) and simply took the outside ones straight down?

I think it might have passed inspection with only the center ones having turn downs also

I chose to have the outside pipes, come between the drives rather than have all 4 basically come out of the transom and make a nice sweeping bend downward was, in my opinion, for "noise". When you passed a member of the water patrol with a db meter, the exhaust was between the drives and directed downward. This system worked. It may look weird but it was very functional and it cured my noise ticket problem. Note, MN noise statutes state that there can be no switchable mufflers on the boat, thus eliminating the "gaffrig" style mufflers. This system seemed to be the best all around approach to any noise problem.

DNR is pretty strict around the Chesapeake and with my dry stellings I'm the loudest on the creek. Usually run open all day long but when I see a lurking water pig I can close them with a switch! Until one of my lines cracked. But lines are changed and re-routed! Looked like a huge RC boat with all the nylon tubing for the dampers.
But here's mine. I never did get a db rating though sorry.

Have you had any issues other than a cracked line with those actuators out in the elements? Who make's that set up? I wish the phone DB meter apps were accurate. If your bored someday try an app. Just curious what you are seeing.

Starting to believe everyone saying a turndown's will be needed to make me legal. But snaking them around my steering won't be simple as just sliding them on. Called Teague today and he doubt's the ST-450 will reduce it enough. He says a full time mufflers would be needed - not interested in this option.

Still wonder about the CPPerformance option??? Anybody believe these can get the job done?

It appears as if you can fabricate your own turndowns. I would go buy some 4" plastic tubing (for measuring purposes only) and see if there is enough room between your drives, the steering cylinders and the transom. I would try to fab a set up, as I did on the Cigarette pictures in the link above, with the 4 pipes between the drives, the center 2 would come at a nice sweeping 90* bend down and the outer pipes over the face of the gimbals and at a 45* angle to the center pipes, not all in a straight line as mine were. Just enough so all pipes fit when the steering is turned lock-to-lock. It is really hard to tell from the picture if there is enough room, but it is really worth a shot to try. If there is enough room you could have the ends of the 4" SS tubing enlarged at a muffler shop to just slip over your existing thru-hulls. Not a lot of cost for the benefit.

No issues at all really. Nylon cracked mainly from storage. Which this was the first season in 3 years. Power is getting a refresh this year so I won't know till beginning of spring maybe. ( crank bearing failure). But it was very quite to me when the dampers where closed. When open is like all hell broke loose! As far as brand I'll have to look tomorrow but pretty sure it was older stellings?

I ran CMI sound elimination mufflers on my scarab for a few years. These are semi-dry 4.5". The videos show both with and without the mufflers. They are quiet at an idle and then above 2000 rpm's they open up to unrestricted flow (and get very loud)

With my DB meter it measured 108 without and 84 with

http://youtu.be/Xy-7UolI1No

http://youtu.be/ZX0sVVShGc4

Going out to watch, and hear, fireworks, and gets a ticket for loud.
Did the pyro company get a ticket as well?