Like he said. they have these baffels inside the big chrome pipe. It is about 6 inches long and about an inch in dia. its crimped at one end and has some holes drilled into the 1 inch pipe, then the 1 inch pipe is connected to a cone to match the inside dia of the muffler/pipes you see on the side of the bikes.
All you have to do is take a plasma, or even a holesaw the right dia to slip into the pipes and cut through the welds and pull it out. Poor mans drag pipes.
There is a company you send the stockers to and $179 later they do what i just said and weld in this little ring to attach a tip to and make it look a little neater.
Most RUBS (rich urban bikers) just take the pipes off, buy some screamin eagles or what ever and bolt them on, instant bad asses. lol
I grew up around harley riders in my family, I hate the way they sound going by. At idle, they sound bad ass, on the pipe most of them sound like a firecracker inside a garbage can.