Recently bought a 1991 Checkmate Convincor with a mildly built 509 mercruiser with a weiland supercharger (4.5psi) boost at the moment (dyno sheet max 787hp)....boat is awsum but way too loud for my lake...have been trying to figure out the best muffler to bolt on to the tips....currently looking at the gibson bullets... and the shotgun mufflers with mechanical flaps by drew marine.....any thoughts and suggestions on which ones are better for noise reduction but won't rob a ton of horsepower.....they will be used on the lake but will be coming off when dipped in the ocean!

Aqua power LTD

Gibson bullets. Friend uses them on his dyno setup for mufflers. Has proved many times they cause zero hp loss.

Well that's good news....should I be worried about having flappers.....the straight pipes have nothing now....

What kind of rpm your turning?

I'm not sure about the zero HP loss, but they do work well and you can use flappers on them.

5900 rpm max on dyno sheet...I haven't done that yet only had it out once and did not push it to its max potential....got kinda scary at 81 mph and backed off lol

This is what you need for your setup.

http://www.offshoreonly.com/forums/s...silencers.html

Check out my add. I have one set ready to go for your application.

My tail pipes are 4.5inch...dammit......and are
These aqua mufflers are considerably better than the gibson mufflers? And just clamps? Wouldn't a thru bolt or two also be a good idea? Don't wanna have them go to the bottom of the lake...

Off by 1/2" in diameter, they would have been perfect for you. As for the clamp... never had a problem with them on my 1993 Cigarette Top Gun, Boat ran close to 100 and I was able to take them off when noise wasn't a concern. Best of both worlds. Plus they sounded and looked great.