I love the roar of my boat when it is idling but I didn't care for the overly loud exhaust when i was cruising down the lake. By the end of the day my crew and i were all def between the music and the exhaust. I have seen many posts on this topic but I didn't see one this inexpensive so i figured i would share. I installed these in my 4" exhaust tubes going from the Sideswipe valve to the exhaust tip. It took me about 30 minutes per side and cost me ~$100 with shipping. I saw no loss in power the boat is somewhat quieter going down the lake but the real magic happens when I switch my exhaust to one side. It almost goes silent. A bit like captains call. I saw almost no reduction in idle sound with both exhaust ports open. Perfect for me.
Here are the silencers I installed: http://www.cpperformance.com/p-12622-4-slip-in-silencer.aspx
Here are some pictures of my install. Basically came down to drilling one hole in the exhaust tube to hold the silencer in place. Hardest part was taking the tubes out. Came down to brute strength and ignorance.