Thought some of you who are looking at different muffler options would like to hear what we did. We installed the replacement HPI tips on our 25' Advantage. We are running a stock 496 HO. Had Advantage do the work on Saturday morning and we launched later that day. Apparently, Mercury has used HPI mufflers when they have done their own testing and (although I don't know for sure) it appears that these will not void your warranty. I would call Merc. to be sure.
We thought we would try the Marina and see how we did.....the gentleman at the booth told us we would have to be tested and we met the guy down in lane 1. Launched the boat, let it warm up a bit and tested at 80db. I was surprised it was that low, but was happy to be well within the range. For the record, the two employees at the marina were very friendly, decent guys. They were professional and even joked with us about the testing, etc.
Only ran the boat for about 1 hour but it looks like we lost about 200rpm's and maybe 2-3 mph. I wasn't happy about that, but it wasn't terrible either. The boat still sounds like a performance boat, just a little quieter. If you have any other questions, let me know.