well...If you are aiming for high top speed then I wouldn't worry about headers. There is a lot more that you are gonna have to replace to get a high top speed. And if you have exhaust then you aren't really gonna be able to hear the headers that well. unless your ear is right next to them. That's just my opinion.
and jayi12-15psi/if you have a turbo then you won't need a headers and they won't really work either. All you have is a turbo exhaust manifold and down pipe. See, turbo's use the exhaust pressure to work. It's a long story.
And one more thing, I'm not totally sure about this but if you have exhaust and headers then you should get more than 15hp. I'm not totally sure. But if you are after inexpensive power go for the CAI. They sound cool too.
Matt
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