Could actually be better off going a tad bigger further back for more expansion room, so the same volume can move even though the exhaust gases lost heat. But, going too big, too soon, forcibly slows everything down.

Back pressure has but one purpose in the world, it IDs those that really know what they're talking about. Velocity is key, not back pressure.

I have a few experiences with "Back pressure"

Muffler baffle came loose internally, restricting flow... drove like crap, lost mpg.

Cat converter clogged... drove like crap, lost mpg.

Some idiot fitted a muffler 1/2 inch under stock size... drove like crap, lost mpg.

Dented exhaust before muffler on rock... drove like crap, lost mpg.

Dented exhaust before muffler on rock, part Deux... actually this happened to the feeder pipes before they joined a collector on a car where they passed under the sump from the front, maybe 18 ins from the exhaust ports... made power band very "notchy" and cut off the top end... BUT... inside the "notch" mpg increased slightly. Had no tach on that car, but it was smooth until 2000 rpmish, then got resistance and stumble, then resonated and pulled like a train between about 2500 and 3500, then stumbled coming out of it, sounded asthmatic in the 4000s and was hitting a brick wall at 5000ish.

since no one else has said it, and its been annoying me..... if you put headers on your 4 banger, it'd better be a V-4 and not an I-4.

and yes, back pressure is something I like for a massage, not my car's exhaust. For that I like velocity.

Had a random thought a long while ago while building up my protege; what rpm band will it primarily operating in? Figure out the intake CFM and exhaust CFM and design manifolds and piping to match that for optimal velocity. Sure, it'll suffer when not in that band, but for what you designed it, it'd be ...many percentages (I have no idea how much better) more efficient than one designed for the entire rpm band. Nascar stock cars tend to stick above 6000rpms and have tuned their open exhaust to promote free flowing, high velocity.

Just a random thought.

^^V4? i never knew they existed in cars?
i think i have to go with everyone else on this that the 4-2-1 header is the best. it gives you low end torque where you really need it in our honda's. i'd go with a DC or just some cheap ebay header.

I've only seen V4s in older (1970s) econboxes in Europe. As far as I know only bikes are made with them now.

Cheap headers are probably NOT going to give you low end torque, they will be too big, they're made for 9000 rpm dyno queens.

yea thats what i was thinking too, and why not put a header on a inline 4?

what kind of header do you recommend for a 1.6 civic? would it have to be custom made? :confused:

If that's a D16, I'd look to see if I could order a D13 or D14 header that would bolt up, or I'd look for a "rally" header, 'coz rally performance guys know better than dyno freaks, or I'd get the cheap eBay header anyway and hammer it a touch flatter on the inside curves where possible. you want about 1 inch primaries, and if you're lucky you'll find 1.25 primaries which are more ideal for 2.0L motors, but will probably find ones with 1.5 inch primaries, because they can sell more to the all knowing "bigger is better" crowd. However, it's area that counts, and deforming 1.25 inch tubes to the same area of 1 inch tubes should work (And due to a quirk of fluid dynamics, may flow better than a header with the same curve radiuses made in 1 inch round tube, because the flattened short side radiuses may flow better)

oh putting a header on a I4 is a good idea. But headers? I've never seen one. header, headers. there's a difference. That's what I was getting at. Currently I have a simple 4-1 header on my protege, but its stock from mazda, (different year) and according to the sheets, only adds power up top above 4000rpms, so not terribly useful for FE.

I beleive a tri Y type header is best for FE as it frees up low to midrange torque. I have one of these on my wagon and it seems to have helped a bit...