I have the clamp on Gibsons and I run 30 to 40 miles at a time across Lake Huron and they stay super tight. I've heard they will knock a few mph of on very high performance blown engines. I haven't checked on mine yet. I take them off when I'm on the big lake and put them on when I get into the river or inland lakes. They do make a big difference, without them I am still loud 5 miles away at WOT.

I have a leftover pair of HPI clamp-on mufflers that would probably work just fine with your tips if you have 1 1/2" protruding. These "bottom" out at 2" of pipe regardless. The company is no longer in business, but they are extremely well made. I ran them on my last boat and they knocked down the 525 exhaust nicely, but it still sounded nice. These have a straight line of sight through the muffler with a claimed reduction of 10 db's. I probably live 10 miles from you if you want to look at them, I'ld sell them since we have a boat with twins now. I use to have a LS7 about 12 years ago that I fixed up with a friends help. We ended up upgrading the power to a 509 with a pro-charger. I think that was pushing the safe limits of that hull ! Send me a PM if you have any interest, I'm going up sledding for the weekend tomorrow.
Steve

How much pipe does Gibson require to clamp to? Is the sound good?

I will send you a PM. Justin

I think they bottom out at a little over 2", I don't know if 1.5" is enough. I'm headed up to where I keep the boat next week. I'll measure them and let you know. As far as the sound, they sound great, they just take the edge off without making it sound to muffled. I think these take me down more than 10db. I measured it when I first bought them, I don't remember the numbers though.

GGBs all the way small and work great , really toned down the pounding .

Is what you are refering to a clamp-on style or threw transom?

This is the only pic I could find of my Borla's.. When I had the swim platform made, I had them include some tabs above the end of the body of the muffflers.. I have straps on them to hold the extra weight. My inner pipes extend about 2" pas the outer and I slipped the 4" mufferls on and double clamped them. With the shotguns on it is very quiet at idle.. At speed the mufflers take the bark out. I did not see any speed increase with them off, but I did not retune and only made a few passes.. Made too much noise with out them...
This is an old picture.. but it does show how I set it up. Not as pretty as the others, but they do quiet it down and I dont believe I lose any power with them.

Dick

Thanks for the pics and the info. The Borlas i was refering to were the threw transom mount style but i would asume that the sound is the same..

What motor are you trying to quiet down ?