Almost every performance freak in America, somehow, from birth, believes headers make a car go faster. Perhaps this is because the 'car geek' gene gets passed down from one generation to another.
If YOU believe headers will make your car go faster, you probably were exposed to V-8 engines. Everyone knows V-8's need headers to make horsepower...
With Honda engines, however, the factory engineers did a masterful job in coming up with an exhaust manifold that delivers excellent power and torque throughout the powerband. This is NOT to say there is no room for improvement --- it's just that the improvement is NOT drastic and 'neck-snapping' as header manufacturers [and your friends] want you to believe.
To understand how a header works, you should know the primary function of the exhaust manifold. The practical theory is both simple AND complex.
Exhaust velocity is the key to making horsepower. If you've read any of my posts, this sounds familiar. Velocity is also the key to performance induction systems. Exhausts systems are merely the case of getting 'bad' air out, instead of getting 'good' air in.
There are two common Honda header design types --- four-tube and Tri-Y. The two designs share benefits, but each is engineered to deliver power for different HP useages.
OE Honda exhaust manifolds are a well-engineered compromise between four-tube and Tri-Y headers, which is why MANY CiViC builders 'feel' little or NO difference when after header is installed. You will only get a 'placebo effect'.
I'm sorry if this news disappoints you...
Sure, aftermarket headers offer the APPEARANCE and TONE of performance, but they won't deliver the massive HP gains ppl expect or what the manufacturers advertise. It's just another hollow promise...