CivicSpoon - I see you are from Syracuse, who the hell are you because I would love to come slap you upside the back of the head. They have differant "firing orders" are you friggen serious? Please explain how putting on an aftermarket header is going to CHANGE how the motor fires?
4-2-1 also known as a "stepped" design, provides for greater midrange power gains over stock - while sacrificing greater top end flow.
4-1 design, best used with motors capable of delivering higher output (higher compression, supercharged etc) has little, if not negative midrange - but a much greater upper range of power.
The numbers represent the type of header, there are 4 pipes leaving the header, since its a 4 cyl motor - thus the "4" in the begining... the "2" in the stepped design means two of those pipes come together - and then the "1" is the output on the header. A 4-1 design is just 4 tubes that converge at one exit point... pictures
4-2-1
4-1
See the differance... it in no way changes the way the motor fires - the header only moves exhaust gases from the head and out your exhaust. The better you are able to clear exhaust gases, the more power your car can create. You could strap on a CAI, cams, cam gears, total head rework etc. But without being able to exhaust that added pressure, the full benefits can not be seen. Modding a car is like a big puzzle - if you dont put the pieces in a certain order you can end up spending big bucks on repitition
(e.g. replacing your springs, but not replacing your shocks while you are at it - since you have to remove both in order to do it... etc)
So CivicSpoon... who/where are you 