Yea, I've been reading about exhaust and back pressure and what not as well. It is not all about back pressure and flow...but how the flow works well with removing the exhaust quickly. You want exhaust to exit as quick as possible. 5" diesel exhaust on our cars is bad, because it is just too slow moving out of the pipes. There is a write up somewhere saying what size pipes are good for how much power. Headers fall under the same concept; slightly smaller pipes, and good merg collecters, to help increase scavenging and flow. Sure, 1 7/8 or 2" exhaust is free flowing, but given a certain application, it is useless. Search around here, and even decent import forums (good write up on this subject here
http://www.hondacivicforum.com/forum...ead.php?t=3064), and on our site go in depth about exhaust, back pressure, scavengin, ect.