Originally posted by /^Blackmagik^\
not exactly... a manifold and a header are two different things. yes they serve basically the same purpose, but the header is less restrictive.
a manifold has a signifigant amount of backpressure because exhaust gases from one cylinder build up pressure in the manifold that affects the next cylinder that uses the manifold. basically all the cylinders dump into a common pipe. the gasses from the exhaust stroke from each cylinder are not evenly spaced in a manifold. this causes the exhaust stroke from each cylinder to interfere with the next.
in a header the pipes are bent and approximately the same length to keep the exhaust stroke from one cylinder from affecting another therefore eliminating a signifigant amount of back pressure.
http://www.dictionary.com/search?q=manifold
manˇiˇfold Pronunciation Key (mn-fld)
n.
A whole composed of diverse elements.
A pipe or chamber having multiple apertures for making connections.
http://www.dictionary.com/search?q=header
headˇer Pronunciation Key (hdr)
n.
One that fits a head on an object.
i guess that's where they got the name for it? so let me get this straight.... the stock jdm it-r 4-1 exhaust manifold (almost equal length), isnt an exhaust manifold? its actually a header? is the it-r 4-2-1 a header or exhaust manifold? but the 4-2-1 looks like the stock one on my accord... which im sure is an exhaust manifold... i bought a GReddy header 4-2-1 for my accord, and its def. not close to equal length. So should GReddy call it a manfold? i do have a dc header for my civic (4-1) which is almost equal length.... blahblahblahblah.....