[8695Beaters]

Three corrections/ additions:

1) The bend in the header does not create the power (well it kind of does, but the bends are there mostly to clear the rest of the engine bay). It's the length that does. A header is basically a tuned pipe. Imagine you are playing a clarinet. If it is out of tune, you adjust the length to bring it back in tune (by pulling out the mouthpiece a hair. The length adjusts the note and therefore the tune). The same idea applies to your engine. Certain harmonics will cause air to flow out of your engine faster at certain RPMs. Nearly all headers are tuned to create peak power in a 500 RPM band. Where that band is depends on how you drive the car and the engine.

2) Dramatic is a relative term here. Think like 15-20 horsepower on a regular four-cylinder. However that ends up being about 15% depending on the engine.

3) As for brands, just open up any good car magazine (my favorite is Sport Compact Car) and look at the ads. Anyone with at least one full page will probably help your car, not hurt it.