||Cost: a lot...
BMW E 34 535i Racing Dynamics headers
The Bmw E34 exhaust is not really restrictive to start with.
The very basic idea behind exhaust tuning is that the exhaust
gas coming out of your engine isn't a stream of gas, it is
made up pulses of gas. These pulses are essentially shock
waves, with high pressure at the front and low pressure behind
it. The low pressure end of one shock wave essentially "pulls"
the next shock wave along. This means the engine has to do
less work to get the exhaust gas out of the car, thus increasing
power. The trick is that all of these pressure waves only
line up at a certain RPM, at and around that RPM is where
you will get the most power increase. The tube length and
diameter is critical for this tuning. This tube length must
be exactly the same for each pipe connected to each exhaust
outlet. A larger diameter tube will tune at a higher RPM,
a smaller diameter tube will tune at a lower RPM. A longer
tube length before the collector will tune at a lower RPM,
a shorter tube will tune at a higher RPM. Tube length is more
critical to tuning than tube diameter.
The BMWs have an exhaust manifold whose job it is to collect
the exhaust gases from each of the exhaust ports of the head
to which it is attached. The manifold is cast iron to reduce
noise and provide some longevity. In a typical exhaust mainfold,
the individul "runner" for an exhaust port is virtually non-existent
and the exhaust gases from all cylinders (on the same bank)
merges within just a few inches - at most.
A header, is composed of dedicated "runners" (tubes) for
each exhaust port. In nearly all header designs, there is
an intent to keep the length of each tube identical and the
same as tubes attached to the other head (if any). There is
a great deal of science around header design and like most
other engine designer choices - it is an issue of compromises.
Length of the tubes and diameter of the tubes as well as the
collector can be varied to optimize torque and HP at different
RPM ranges. Of course all of this extra *plumbing* usually
has to fit in a rather confined space - which presents additional
Installing aftermarket headers from RD or supersprint will
give you a performance gain. Reducing the pressure from the
cat back makes it easier for your engine to push exhaust gases
out, this really on helps at high rpms. Headers makes the
exhaust gases come together more smoothly than stock before
entering the cat. Exhaust systems to have small gains on stock
engines, but if you are planning on NOS, turbo, or supercharger,
you can expects your 10 hp exhaust to produce something like
30 and 50hp.
|Does Muffler give more HP?
Sorry to disapoint you, but the answer, simply, is no. The
most efficient mufflers can only employ the same scavenging
effect as a header, to help slightly overcome the loss of
efficiency introduced into the system as back pressure. But
no engine makes more power with a muffler than an open header
There is three types of muffler:
Absorption mufflers are the simplest. the construction
consists of a perforated tube that goes through a can filled
with a packing material, such as fiberglass or steel wool.
This is similar to simply punching holes in your exhaust pipe,
then wrapping it up with insulation.
Restriction mufflers: Obviously, a restrictive
muffler doesn't require much engineering expertise, and is
almost always the least expensive to manufacture. Thus, we
find restrictive mufflers on almost all OEM exhaust systems.
Reflection mufflers: Probably the most sophisticated
type of muffler. They often utilize absorption principles
in conjunction with reflection to make the ultimate high-performance
silencer. Sound is a wave. And when two like waves collide,
they will "cancel" each other and leave nothing to call a
corpse but a spot of low-grade heat.
|An exhaust resonator is used in some exhaust stystems
to change the tone and timber of the exhaust sound. The resonator
helps reduce the annoying vibrations of exhaust gas pulses with
a length of perforated tubing inside an expansion chamber. The
exhaust gasses partially escape the tubing diameter through
the perforations into the expansion chamber. In the expansion
chamber, the exhaust gasses expand and change tone. When the
gasses re-enter the tubing, they rejoin the exhaust flow and
dampen the vibrations of the combined flow, creating a more
(Thanks to www.nsxprime.com & Justin)
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