If you insist on using drag pipes on your bike, there is something you can do to improve the low and mid range power produced by the engine. Results have been confirmed by dyno results . If you are serious about making horsepower on the street with your Harley-Davidson, drag pipes will not fit into your engine program plans. Serious street power requires a serious exhaust system.
Drag pipes do have their place.
It is on the drag strip where the engine runs in a very narrow RPM band. On the street, stick with proven winners. Dyno testing of exhaust systems for EVO and Twin Cam engines is now available. The first item to get modified or changed on most new Harley-Davidson motorcycles is the exhaust system. Getting the proper Harley sound always seems to require increasing the decibel level out the exhaust, with many riders installing drag pipes as the exhaust system for the proper sound.