What does a header do? It allows your engine to expell gases efficiently. The flow from the engine comes through the headers, to the catalytic converter and out your exhaust. The better we make the process of moving the gases out, the better your Honda Fit performs. A header can easily bump up the power and torque the car produces.
An efficient header allows hot gases to move quickly, allowing for more power.
Two good articles on Headers can be found on Team-Integra:
Which ever way you go with a header, you have a number of choices: OEM Headers, 4-2-1, 4-1 and racing headers. Normally 4-1 header produce power higher in the RPM band, while 4-2-1 are more for a lower bump in power.
4-2-1 Headers / 4-1 Headers:
Borla Exhaust Performance Header
DC Sports Headers
Choose the right Header that will work with the exhaust system you choose to make an efficient system of power production!