NZ Hot Rod – August 2019

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

> 39

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.