Making your Harley pipes louder doesn't necessarily mean that you have to spend a lot of money. What's key, however, is understanding the various options one has as well as understanding what your exhaust system does. Three ways of making your Harley pipes louder are retuning the engine, removing the baffles or by swapping out baffles on certain models of Harley-Davidson motorcycles.
Retune the engine to make Harley pipes louder while improving performance. Out of the factory the Harley Davidson is tuned to meet requirements for noise reduction and emissions standards. To do so, the electronic control unit (ECU) optimises the air and fuel intakes into the motor for these purposes. By retuning the bike to peak performance with the addition of an computer control unit, you can both make the biker louder and deliver more power. Control units that change the fuel and air flow through the engine are available at dealerships and can be found online.
Remove the baffles or drill holes in them to increase air flow through the pipes. By doing so, the motorcycle's pipes will be very loud. However, while drilling out the baffles or drilling holes in them will make the Harley louder, it will not improve performance. In fact, over time the performance of the Harley will drop off.
Attach slip on mufflers. There are a number of aftermarket slip on mufflers--some with removable baffles that can be swapped out. Slip on mufflers go on the end of the Harley-header pipes. They are a less expensive alternative to completely installing new pipes. Upon doing so, the engine will need to be retuned to adjust for the new airflow through the fuel and exhaust systems. Slips-on mufflers make your Harley pipes louder and improve performance with out swapping out the entire exhaust system.