Common sense would tell U that longer pipes puts more noise behind Ya when riding.

When I added cams they made the pipes louder.

 

mine is a 88ci and i have 1 3/4 drag pipes on mine with no baffles, i have not heard another bike as loud as mine....i love the sound as does anyone who hears my bike. i just dont care so much for the style of them. now that they are wrapped they look ok but im leaning on getting V&H big radious 2-2 with no baffles wrapping them black. your bike probably sounds great to everyone else but you, try letting someone else run it down the street for ya and listen to it, or you could always take the baffles out just to hear the differance, if you like the way it sounds then i would adjust your A/F mixture....only thing your gonna lose out on is a little bit of power

 

Its all about acoustics. A larger diameter pipe will have deeper tone than a smaller one. A higher frequency sounds louder than a lower one at the same decibels. Loudness is about unrestricted airflow which is a deal breaker when it comes to performance.

 

loudness is effected by a lot of things.. mostly is the muffler or lack of it. engine size, compression, cam have a lot to do with the extreme ear piercing bikes that you always hear pulling out going down the road at bike nites.. as far as getting the most sound out of drag pipes, big diameter,and short pipes with few bends will make the most noise.. i think the stock cvo mufflers on my EG is plenty. but i am pretty sure i'm turning into one of those cratchity old men..

 

Removing baffles and replacing them with Thunder Torque Inserts is an inexpensive way ($20) to get some decent sound, and they also will INCREASE your low & mid Range Torque and HP.

Check out this vid, toward the end is what a stock 103 sounds like with Rush slip ons and no baffles with the TTI's installed.

http://www.youtube.com/watch?v=M6VwWeIyjeU

Check out the increase in torque & hp on this dyno chart of an 88 ci

 

I like Big City Thunder's original baffles (no affiliation)

 

big city thunder monster baffles.... You'll love them, Your neighbors won't !!!!

 

That answers the question right there. Given the same size pipes, the bigger lungs will produce a bigger sound.

 

All exhaust systems being equal, cams usually have more to do with volume than anything else.
It goes like this:
Cam timing can build static compression, as well as lower static compression, no matter what the CID is..
The exhaust valve opening timing sets the volume.
SE 204 cams being the loudest I've heard..