Why is my 2012 FXDC much quieter than my 2004 XL 1200 Roadster when they both have Vance & Hines slip-ons with the same standard ( loud ) baffles in ? Don't get me wrong , the Dyna sounds great and it's much quieter mechanically but I would have thought 1,585 cc's would have made a bit more of a bang than 1,200 . Thoughts anyone ?

 

As the old saying goes.
“Dynamite comes in small packages”.

 

The cat in the exhaust will dampen down the sound level. Get rid of it and you'll be happier with the sound.

 

Where is the cat ? I thought it was in the mufflers . Is it in the headers ? ( Silencers , downpipes )

 

Different compression ratios, cam specs, and volume of air moving. A larger volume of air moving creates a deeper tone, while a smaller volume moving creates a higher tone/ pitch which can sound sharper/ louder to the ear. Also even though you have the “same set” of pipes on both bikes I’ll bet the set on the dyna has more tube length, which again can reduce heard sound. As well as does the sporty have considerably more miles on the pipes? The packing inside the baffle is likely burnt out, while the dyna still has some left. (Can’t remember if the V&Houd baffles have packing or no)

Probably a combination of all of the above if I had to guess.