I thought I remembered when I had a 1989 24' Sunsation Rocket in the early 90's when I switched from thru hull with no mufflers to thru the prop the difference was like 1mph. This was with a stock 454 330hp bravo 1 and the boat was 7ft beam and about 3200lbs. More than likely on a larger heavier boat the change will be not measurable.

Bravo 3 is good to a solid 65 mph before they reach their limit of effectiveness.

Leave it alone. Boat cheaply. More power to you. Besides, soon enough we'll "have" to have mufflers anyways. Switchable exhaust doesn't count. Or you could spend that cash on a K*** A** stereo and throw in a recording of a Top Fueler.

Exhaust = $$$$ + stereo to keep up = $$$ + noise ticket = $$$ + new mufflers = $$$$$$$$$$$$

Isn't boating fun?

The stock "Y" pipe exhaust on big block Mercruisers is good to about 350hp. If your motor is less hp than that, you will likely get zero performance increase by going thru transom.

I don't really like seeing a slow boat making loud nascar noises.

If a boat will haul tail, then sure let's make it loud. But our lake has a lot of 45 mph boats with loud exhausts. About the only good thing I can say about that is that the swimmers will hear them coming far enough away that they can swim out of their path.

MC

Loud pipes save lives.

Loud pipes risk rights..

In my experience, at that hp level and the weight of the boat you will not see any increase in speed at all. The stock thru prop exhaust flows just fine for the mild power of a 7.4 Merc.

Years back, I had a new Baja Sport 280 w/7.4L's It was ordered with thru prop exhaust. I had installed the Corsa silent choice system and saw zero gains in speed.

At the time, Gil Marine was advertising speed gains of up to 7 mph with their "Magnum" system. I spent close to 6 grand and still saw no increase in speed.

Unless you are adding more hp, there is no need to spend the money.

...personally, I dislike boats that make lots of noise when there is no need to. Loud, slow boats are not cool.

My wife and I purchased a 2000 330SS and had Bravo I installed. After rebuilding the 454's to 489's we added some CMI tips and diverters after the stock exhaust manifold. Switching the diverter from below water exhaust to above water exhaust gave us about 0.2 on the gps. If you look at the tack very closely you can almost see the needle move.

It'll sound quicker, so you'll convince yourself there's a gain.

that is what I have read as well,,makes sense since the only people saying they picked up mph have 502s
which make more hp than that.