hey guys after reading the backpressure myth stickieI was wondering that if i just got a megan 4-1 header and keptmy stock exhaustpiping, wouldn't I get more power in the lower RPM range since smaller piping means high velocity and more power at lower rpm range? Has anyone ever tried this? it beats getting a 4-2-1 headersince 4-2-1are expensive... BTW I have an 04 civic ex and want more power at lower rpm range...

 

backpressure is all about finding the perfect balance between flow and velocity. Stock piping has low flow, but high velocity, 4" piping has high flow but super low velocity, but for an N/A civic with I/H/E, 2.25" would probably be the best balance with high flow, and pretty good velocity at the same time. Theres a chart around here somewhere that lists what size piping is best for how much HP you have, but idk where it is....

 

a magnaflow catback will give you good low end gains, i have an 02 DX with aem SRI and magnaflow catback, with megan 4-1 race header and downpipe coming in the mail. with just the intake and exhaust, its a quick car, keeps up with base line teg's and loses to cavy Z24's by 2 car lengths, cant go wrong with i/h/e

 

with the big header and small exhaust your gonna create adverse effects in the flow. not a horrible amount but the hot gases are gonna exit out fast and than have to funnel into the stock exhaust. this will create back pressure and not the exhaust gas velocity, most valued for the engine. with that effet, you will lose the exhaust scavenging effect and will not realize the full potential of the engines power.

either stick with the stock exhaust or just a catback but not just the header IMO. but the exhaust will only flow as good as it's smallest part, so try to match the exhaust up as best as possible to keep things flowing smoothly and without obstruction. Your best bet is 2" to 2.25" becuase most header collectors are in that range. you don't want to create an area that acts as a bottleneck or as a pressure canceller, as this will limit the whole engine ability to make power. Not only in the exhaust but will affect the intake as well.

I hope that helps. if you have anymore questions feel free to ask.

 

^^^ 100% correct ; ) i have that exact setup as he said, I/H/E 2.25 piping. stock cat, and threw in a new 18' resonator. sounds awesome, and great gains from that