More power at the top end!
Headers (also known as the Exhaust manifold) are a worth while upgrade that
will help bring out more horsepower and torque. Headers have a slight increase
in diameter over that will help flow more of the exhaust gasses over stock.
There are a couple different kinds of headers that you’ve probably seen
such as: One Piece, Two Piece, Equal Length and Un-Equal length. One Piece means
that the Header and the up-pipe come as one piece, you can’t separate
them. “Two piece” means the exact opposite. Either the Header will
come by itself, or it will come with an up-pipe that will have to be bolted
to it for installation. For example: The Invidia Header unit comes as one solid
piece. Notice how the up-pipe is welded on so it is “One Piece”,
and when you look at the APS unit, it has the Header and the up-pipe as two
separate pieces. Some “Two Piece” units have to be bought with the
right up-pipe because it will not bolt up to any other up-pipe.
“Equal Length” and “Un-Equal Length” are pretty much
self explanatory. “Equal Length” means that both lengths of pipe
that come off the block are of equal length such as the PERRIN header, and yup
you guessed it “Un-Equal” mans that the length of pipe that comes
off the block are un-equal.
The unequal length header is what gives you the “Boxer Rumble”
we love. I think PERRIN gives a good description of what happens: “Because
of the unequal nature of the OEM header, the exhaust pulses are paired together
causing that lump sound. The PERRIN header changes the note of the exhaust because
of it equal length design. The sound pulses from the exhaust are equalized and
spread out, causing the smoother, more refined sound coming from the exhaust”.
Headers are usually good for about 10-15hp and will help you out in your top
Invidia "One Piece Header"
PERRIN "Equal Length" Header Borla "Un-Equal Length" Header
APSTwo Piece Equal Length Header installed on a STi