I have a 2002 Honda Civic EX and am looking to upgrade it for gas mileage. I already installed an AEM shortram intake and am looking at DC headers and an HKS catback.
1. What is the difference between 4-2-1 and 4-1 headers? I have come across conflicting information.
2. What is the difference (aside from the number of parts) between two piece and one piece headers?
3. Does it matter which upgrade I install first?
Any suggestions are welcomed.