NZ Hot Rod – August 2019

(Axel Boer) #1
it) is transferred through the louvers
in the inner tube and is eventually
absorbed by the packing material.
Unfortunately, that’s where the trouble
begins. The old system of louvers
restricted the flow (some louver designs
were and still are more restrictive than
others), but the inner pipe which is
sandwiched inside the muffler was (and
in many cases, still “is”) often much
smaller than the inlet and outlet sizes.
In the end, some supposedly “big” glass
packs might have a true inside diameter
which’s over an inch smaller than
the inlet or outlet ports (taking into
account the side of the louvers which
protrude into the exhaust stream).

In direct contrast is Hooker’s modern
take on the glass pack system. Instead
of a punched louver interior, Hooker’s
VR304 series mufflers along with their
Maximum Flow muffler line-up make
use of a stainless steel internal core.
The core is perforated with a series
of punched holes (no louvers hanging
down and interfering with exhaust
flow or interrupting exhaust pulses).
That core is the same diameter as the
inlet and the outlet (that means a 3-inch
muffler really is a 3-inch muffler. The
case on the VR mufflers is stainless steel
while the Maximum Flow muffler is
based upon an aluminised steel case.
Between the core and the case, these

mufflers are filled with a specialised
form of packing made from stainless
steel and high temperature glass. It
lasts far longer than the traditional rock
wool packing used in other mufflers.
The end result is an exceptionally high
flowing muffler design (in fact, this
design is one of the highest flowing
mufflers out there; period). Hooker
notes this muffler actually flows 99%
of a section of 2-1/2-inch open pipe.
Fitted to a car, they’ll typically produce
more torque and more outright power
than that pipe too. They’re quiet at idle
and have very little resonance. Under
power, you’ll find the tone is mellow.
Some companies use the pressure
and sound energy released from the
engine’s combustion chamber into
the exhaust system to create a low-
pressure area between exhaust pulses.
Manufactures of these systems claim
this arrangement helps scavenge or pull
spent gases out of each cylinder. Instead
of using ceramic, fibreglass or steel
fibres to act as baffles, these mufflers
use of a sequence of internal chambers
to control the sound. Beginning at
the front of the muffler, a resonant
tuning chamber is incorporated.
This chamber captures and cancels
specific sound frequencies, reducing
resonance inside the vehicle. Next is
a power chamber. According to the
manufacturers, this area of the muffler
creates a negative pressure which helps
scavenge exhaust gases for increased
horsepower and torque. One more
chamber often follows: Here, a series
of delta-shaped internal deflectors are

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Many mufflers look similar from the outside, but the differences internally can be staggering.
The left muffler is a Hooker Aero Chamber. The centre muffler is a Hooker Maximum Flow while the
muffler on the right is a Hooker VR series.


Internally, the Maximum Flow and VR mufflers
incorporate a special perforated stainless
steel core. In turn, that core is surrounded
with a composite high temperature fibreglass/
stainless packing. These are one of the highest
flowing muffler configurations available.

This [extremely] high tech Hooker Aero Chamber muffler is based upon a series of internal lens and
various chambers to actually enhance the aerodynamics of the exhaust gases before they’re expelled
(much like a “stepped” racing header). Simultaneously, they use special internal chambers within the
mufflers to cancel out unwanted frequencies and amplitudes.

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