[bobcowan]

15dB is a lot. Remember that the scale is not linear, it's logorithmic. To lose 15 Db, you're going to have to work at it. There's no off the shelf baffle that you can stick in the pipe to do what you want.

You're going to need some new mufflers. The two most popular seem to be the spiral/auger type, and the Cobra Pack glass packs. I installed 32" Cobra Packs in mine. A big job, but made a big differance in sound volume and quality. I don't have a dB meter.

Another trick is to bolt on a piece of alum about 4" in front of the pipe opening to act as a baffle. That breaks up the sound waves and the meter reads lower.