First of all, you have to understand that it is not as simple as bolting-on and expect huge gains in power. Upgrading your exhaust system will take a considerable amount of tuning which largely depends on your engine's stock output.
Surprisingly, aftermarket headers can turn out to be too good for the engine that you end up losing more power. This is why you have to tune it with a dyno test to determine its effectiveness.
There are also several types of headers. The 4-2-1 is aimed for mid range power, a 4-1 is for top end and so on.
For me, in the end, tuning is everything which is why I would suggest that you research about this extensively so that you would know what you want, what to expect from your set-up.
But once you get it right, the advantage is of course the expected power gain, you get a more throaty sound when coupled with the proper pipe diameter and muffler.
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Last edited by Memphis Raines; March 16th, 2009 at 12:51 PM.
Reason: spelling