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It wasn’t that long ago that exhaust systems in general and mufflers in particular were considered a necessary evil with the performance crowd. Noise meant power. Or at least, that was the consensus. On the other hand, a quiet exhaust system certainly does have a number of positive attributes: It keeps your ears from ringing incessantly, it promotes friendly relations with your neighbors (more or less), and equally important, it keeps the boys-in-blue off your back. Good news, we’d say.
Unfortunately, many original equipment production-based muffler configurations (along with inexpensive replacement systems) also soak up valuable horsepower. That’s no secret to anyone reading these pages. Other than keeping the noise down to a dull roar, the main objective of an exhaust system is to "cleanse" the combustion chamber during the exhaust stroke. This "blow down" creates the ideal environment for the fresh air-fuel charge to be introduced into the chamber during the intake stroke. Clean out the combustion chamber efficiently, don't plug up the exhaust and you make more power. That’s the basic concept. But the reality is you can also make plenty of unwanted racket if you’re not careful.
How do you clean out the combustion chamber, maintain decent flow through the exhaust and still keep things quiet (and legal)? It’s not that easy - especially when high performance cars are concerned - but today high tech exhaust system manufacturers such as Hooker Headers have a number of equally high tech answers.
Seriously, not much can outflow a straight section of pipe. The trouble is, an open section of pipe does little when it comes to the sounds of silence. One type of exhaust "silencing" that was once overlooked is absorption technology. When you first think about "absorption" mufflers, you automatically consider the old straight-through glass pack designs. They've been available forever. In practice, a glass pack includes a pair of tubes - one inside the other. The inner tube is punched with louvers, and sandwiched between the tubes is a packing material (almost always made from fiberglass). As the spent gasses pass through the muffler, the sound (or at least some of it) is transferred through the louvers in the inner tube and 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 that 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 that'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 lineup, 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 aluminized steel case. Between the core and the case, these mufflers are filled with a specialized 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, fiberglass or steel fibers 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 that helps scavenge exhaust gases for increased horsepower and torque. One more chamber often follows: Here, a series of delta-shaped internal deflectors are strategically located in order to cancel noise by separating, then recombining pulses. Finally, a low-pressure balance chamber is usually incorporated at the rear of the muffler. This chamber is designed to block atmospheric pressure from moving back into the system.
Hooker Headers’ high tech take on this is their Aero Chamber muffler. Here, as exhaust enters the muffler, it encounters an aerodynamic lens that directs sound pressure waves into what is called an “acceleration chamber.” The stepped acceleration chamber then increases the velocity of the exhaust, promoting maximum flow. An internal resonance chamber coupled with a tuning tube cancels unwanted frequencies and amplitudes. In place of louvers, these mufflers use a large stainless chamber perforated with small holes. This is the sound absorption chamber, which quells high frequency sound waves. Since there are no louver edges dropping into the exhaust flow path, there is no restriction in the flow of exhaust gas. But at the same time, the perforations still allow the sound to be absorbed. At the tail end of the muffler, another aerodynamic lens directs sound pressure waves out of the muffler.
The result of the Aero Chamber arrangement is maximum scavenging and added torque in many applications. In terms of construction, the internal chambers are built from stainless steel while the case is constructed from 16-gauge aluminized steel. As far as sound is concerned, this muffler will not drone at cruising speeds and the internal sound absorption chamber eliminates the high frequency sound waves that tend to make that tin can sound we’re all familiar with. What you’ll end up with is a deep, throaty exhaust note. Typically, the Aero Chamber is also an extremely high flowing design – second only to the Maximum Flow design mentioned above.
In terms of weight and dimensions, here’s how our trio of Hooker high flow mufflers measured up:
Muffler * Weight * Length * Width * Height
VR304 * 5.5 lbs. * 14.00-inch * 9.00-inch * 4.25-inch
Maximum Flow * 8.5 lbs. * 14.375-inch * 10.625-inch * 5.00-inch
Aero Chamber * 12 lbs. * 14.375-inch * 10.625-inch * 5.00-inch
Today, aftermarket manufacturers such as Hooker Headers go to great lengths to produce mufflers and exhaust systems that out-perform OEM pieces. Case-in-point is this trio of mufflers from Hooker Headers.
Many mufflers look similar from the outside, but the differences internally can be staggering. The left muffler is a Hooker Aero Chamber. The center muffler is a Hooker Maximum Flow while the muffler on the right is a Hooker VR series.
This high tech Hooker Aero Chamber muffler is based upon a series of internal lenses 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.
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 fiberglass/stainless packing. This is one of the highest flowing muffler configurations available.
On the outside, the Aero Chamber and Maximum Flow make use of the same heavy duty 16-gauge aluminized steel case. Both measure 14.375 inches long by 10.625 inches wide by 5.00 inches tall.
Maximum flow mufflers are not “directional.” That means you can install them in any direction you choose (there is no dedicated “IN” or “OUT”).
Aero Chamber mufflers are directional; they can only be installed in one direction.
