Choosing the right muffler

[Yeo]

Sourced from http://www.enjoythedrive.com

Choosing The Right Muffler
How to get the sound and performance you desire.

If you�re running on the street--or in many racing series--you need mufflers. They also come in handy during long drives, when the drone of the exhaust can be downright exhausting.

But which muffler should you choose? It depends on your taste, your engine, the space available on your vehicle and how you use that vehicle, too.

After all, a muffler can be used to tune your engine�s powerband, so that it makes more peak power (a good goal if you�re drag racing or hitting the Autobahn) or more midrange torque (preferable if you�re road racing or driving on the street). By its nature, a muffler also will have a profound impact on the way your vehicle sounds. Often, you can find several mufflers that provide comparable performance for your application, but one is quiet, one�s loud and another is somewhere in between. Hi-po mufflers offer some other advantages over stock units, too. For starters, most hi-po models will last considerably longer. Some even come with a lifetime or million-mile warranty. Performance mufflers also can improve your vehicle�s fuel economy by helping the engine become more efficient. And because some mufflers come with exhaust tips already attached, a simple swap can make a styling statement, too.

* Muffler Designs
A muffler�s purpose is, quite simply, to muffle the noise produced by the engine. When it comes to high-performance mufflers, there are essentially three designs: cancellation, absorption and diffusion.

A cancellation muffler features chambers inside, which tune and cancel various sound frequencies.


In an absorption muffler, the exhaust passes through a perforated tube that�s wrapped in sound-deadening material. Various kinds of packing material are used to absorb sound, including fiberglass (hence the term �glasspack�), stainless steel mesh and ceramic products. Absorption mufflers often feature a straight-through design. Some hybrid models, including �turbo muffler� designs, also use cancellation-style chambers to help muffle sound.


A diffusion muffler uses diffuser plates at the end to split up the sound so it follows many different paths. The sound coming out of this type of muffler can be tuned by adding or subtracting diffuser plates. (Contrary to what you might imagine, you get a quieter exhaust system by running fewer discs.) Some hybrid diffuser mufflers also use absorption material to reduce decibel levels even further.


* Better Performance & Gas Mileage
Virtually all factory mufflers are designed to be quiet. Power is a secondary concern. This means you typically can reap performance benefits by swapping mufflers.

How does a muffler improve performance? At the most basic level, by increasing exhaust flow. Virtually all specialty equipment mufflers are less restrictive than stock-style units. Because more exhaust can pass through at a given time, backpressure in the exhaust system is reduced. Some hi-po mufflers even create a scavenging effect.

The difference between a stock muffler and a hi-po unit can be considerable. For instance, Corsa Performance says its Power-Pulse mufflers for the Corvette LS1 engine flow 45 percent more exhaust than the stock Corvette system. Powertone says its patented open-chamber-design mufflers provide an 8 to 10 percent increase in horsepower, with improved throttle response and better gas mileage.

And Edelbrock says its RPM Series mufflers net a typical 0-to-60 improvement of .24 second on a 1989 5.0 Mustang and .43 second on a 1993 5.7 liter V8 Camaro. On the dyno, the company says, �From 4500 rpm up, our 3-inch center in/out [RPM Series] muffler made more torque than a 3-inch straight pipe, with a maximum improvement of 11 lb.-ft. at 5000 rpm.�

* Scavenging Effect
The ultimate performance gains are to be found when an exhaust system, including the mufflers, creates a scavenging effect. This can increase horsepower, torque and fuel economy, all at the same time.

�Scavenging is when a [reflective] low-pressure wave comes back up the header pipe,� says Kevin McClelland of Flowmaster. �You want it to get back to the exhaust valve when the engine is in overlap. It creates a low-pressure area at the exhaust valve and aids in the induction charge, ... getting your intake flow started into the cylinder.�

The diameter and length of your exhaust pipes, your muffler design and your cam timing are all factors that affect scavenging.

�When you get this optimized,� says McClelland, �you can get a boost in torque. Between that tuning and the intake manifold tuning, that�s how you can achieve over 100 perfect volumetric efficiency on a naturally aspirated engine.� A variety of high-performance mufflers are designed to enhance this scavenging effect.

* Backpressure
When it comes to an exhaust system, backpressure typically reduces performance. �The backpressure on the exhaust flow can help to reduce sound, but at the same time, it limits engine power,� says MagnaFlow. �This power reduction comes from an inefficient burn in the combustion chamber, where spent exhaust gasses are backed up into the combustion chamber and contaminate the next burn cycle.�

What causes backpressure? �It is often the result of restrictions to exhaust flow,� says MagnaFlow, �which results in pressure buildup in front of the restriction. Turbulence entering or leaving a system component or abrupt changes in the direction of exhaust flow may also add to backpressure in the system.�

According to the company, �A second problem associated with backpressure is heat buildup. ... The heat builds up in the muffler and then backs itself up through the entire exhaust system to the exhaust manifold and engine. This heat retention causes damage to the muffler, as well as the catalytic converter, the system tubing, the manifold and gaskets. Even ignition wires can burn up due to an overheated, inefficient exhaust system.�

* Where Do You Want Your Power?
Some mufflers are designed to enhance peak power, while others improve mid-range torque.

A'PEX says, "In tuning, every gain usually sacrifices another aspect of performance. Some sacrifices may be low-end power in exchange for a high-end punch. Other examples could include midrange torque for peak horsepower. In any case, it is important for the customer to know exactly WHERE the sacrifices of a particular exhaust would occur and WHY. Drag racing exhaust systems would want power on the top end, while a road racer would want plenty of midrange torque to propel them through the corners."

Even on street cars, you may prefer top-end power, or you may want more grunt off the line.

The key is to ask how a muffler is going to affect your vehicle�s powerband.

* Bigger Is Not Always Better
We've all heard rumors of people who swap on a bigger exhaust system and actually lose power. How can this be?

"An engine needs a certain amount of backpressure , or resistance to flow, below the torque peak of the engine," says Kevin McClelland of Flowmaster. �When you take away that restriction, ... the engine loses quite a bit of performance below torque peak, which is right where you drive for gas mileage and towing, when you�re just driving around stoplight to stoplight, accelerating away from a stop.

"An oversize exhaust will not hinder performance at high rpm. An oversize exhaust system would do about the same at high rpm, but you would lose power at low rpm. So the bigger is better theory doesn�t work on exhaust systems."

And we aren�t just talking about 1 or 2 lb-ft of torque, either. "If your engine�s torque peak is 4500 rpm," says McClelland, "you spend a lot of time below that peak, which is where you lose your performance. And it can be significant. We've seen losses of 20 or 30 lb-ft of torque, and if your engine only makes 150 lb-ft to begin with, you�re losing 20 percent." The key, once again, is to get the right muffler for your vehicle, your engine and any modifications you�ve made.

* Getting The Right Sound
The question is: Do you want to go stealth or do you want to turn heads? Many manufacturers offer a variety of muffler designs, some of which are markedly louder than others.

As a general rule of thumb, Edelbrock says, �Offset mufflers (single or dual offset) will generally run a few decibels quieter than center/center mufflers. They should be used whenever sound is a greater consideration than maximum power. Center/center mufflers will outflow offset mufflers and should be used whenever maximum performance is a greater consideration than sound.�

The size of the inlet pipe going into the muffler also has an effect on sound. If you want a quieter sound, Edelbrock says to use a smaller inlet tube diameter.

Another consideration: Some companies offer an absorption-style muffler with two or three--or even no--expansion chambers. A muffler with more expansion chambers will be quieter, while one without any is going to be much louder. Also be aware that sound levels can vary according to engine speed. Many manufacturers note that their mufflers are quiet at idle and at cruising speeds, but produce a �bold� or �aggressive� sound during hard acceleration and at high rpm�s. Another thing to consider is how the muffler sounds from both inside and outside your vehicle. Flowmaster says, �The source of the [exterior sound level] is primarily from the exhaust exit. ... The source of the [interior sound level] is less from the exhaust exit, and more from the resonance that is generated within the muffler and transmitted into the vehicle interior.� While you may think louder is always better, remember that interior resonance does cause driver fatigue, not to mention a sore throat from shouting at your passengers. If you�re going to be driving this vehicle on a regular basis, you may want to find a muffler that provides plenty of exterior sound level but keeps things relatively quiet inside. You also can install a heat shield between the muffler and your vehicle�s floorpan to reduce the amount of noise transmitted to the interior. One last thing to think about, when it comes to sound level is the law in your state .

* Materials
Over the years, stock mufflers have displayed an unhappy tendency to rust out. Newer designs are more durable than their forebears. But the short-lived units of the past certainly emphasize the importance of a muffler�s material.

�Exhaust gases are a mixture of moisture, unburned hydrocarbons, carbon monoxide and oxides of nitrogen,� says Bassani. �In exhaust systems, particularly on cars that are driven short distances, these gases condense and corrode mufflers from within. In fact, mufflers collect more moisture than any other exhaust component.� Road salt also does a number on mufflers, attacking them from the outside.

To resist corrosion, most performance mufflers are made from galvanized, aluminized or stainless steel. Some also feature a rust-inhibitor coating. If you live in the Salt Belt, it�s probably wise to look for a muffler with a lifetime warranty against rust-through.

If you�re shopping for an absorption-type muffler, also ask about the durability of the sound-deadening materials that are used. Some packing materials will last longer than others.

* Will It Fit?
Obviously, mufflers come in different sizes and shapes. That�s why it�s important to look under your vehicle--or check with the manufacturer�s tech department regarding dimensions--before you buy.

Many mufflers are available in a variety of configurations, with single or dual outlets, and with offset or center-to-center inlet and outlet designs. Some companies offer different tubing diameters and different case lengths, as well. You�ll need to choose the right combination of options, especially if the rest of your exhaust system is stock. After all, you�ll need to match the muffler to the pipe coming off your catalytic converter (or, in cat-free applications, to the pipe coming off your header collector).

It�s also important to have sufficient ground clearance, since beating your muffler against curbs and speed bumps will severely affect its longevity. Several manufacturers offer low-profile designs--or models with offset outlet locations--specifically to accommodate the in-the-weeds crowd.

* Single Or Dual Exhaust
Typically, a vehicle with single exhaust has one muffler and a vehicle with dual exhaust has two. But there�s an exception to every rule. Sometimes, space considerations under a vehicle--typically a pickup truck or SUV--force automakers to run dual exhaust through a single muffler. That�s why some mufflers are available with dual inlets.

If you have single exhaust on your vehicle but prefer the look of dual exhaust, you can swap on a muffler with dual outlets. Just be sure there�s room for two tailpipes. For instance, PaceSetter notes that on trucks, you need to watch out for interference with your spare tire, hitch and bumper or roll pan.

* Is It Legal?
If you�re looking for mufflers for a car or truck that�s driven on public roads, you�re going to want something that�s street legal. These mufflers have been certified, usually by the California Air Resources Board (CARB), as not adversely affecting a vehicle�s emissions.

Virtually all mufflers on the market that are designed for street vehicles are 50-state-legal, but those that are designed specifically for full-time race vehicles are not.

Of course, emissions aren�t the only issue, when it comes to mufflers. Some states also place limits on a vehicle�s sound output. If you�re concerned about the decibel levels generated by a particular muffler in your application, be sure to check with the manufacturer or retailer regarding the laws in your state.

* Street/Strip Designs
If you drive your vehicle on the street but also race it, you may want a muffler that can be disconnected quickly, so you can run open exhaust on the track.

For instance, Flowtech offers a line of mufflers called Race Readies. �Race Readies let you keep your exhaust system closed for the street, but wide open for the strip,� the company says. �You're just three wing nuts away from power and performance.�

Of course, many racing series and tracks require mufflers. That�s why a number of companies have developed products designed specifically to run while you�re racing.

* Racing Mufflers
Many racing series now require mufflers, so it�s only natural that manufacturers have created some ultra-high-performance race-only designs.

The good news: Bolting mufflers on a race car doesn�t have to harm its performance. Borla Performance says, �[Our] uninterrupted highest flow straight-through patented design has been tested again and again to actually out-flow a straight piece of pipe.�

Running mufflers on a race car also has been shown to reduce driver fatigue, which is important in longer oval track and road course events. Plus, with a quieter exhaust, you can better hear what the rest of your race car is doing.

Most racing mufflers feature a straight-through absorption design, but there are some cancellation-type mufflers available, too. Racing mufflers typically come in round, oval, bullet and collector muffler configurations.

Collector mufflers are used in drag racing applications, and they mount right after the headers. In races that involve turns, bullet-style mufflers are the design of choice for really tight spaces. Unfortunately, they�re considerably louder than round and oval designs, which tend to include chambers in addition to the sound-absorbing packing material.

Durability is another concern. Running at high rpm�s for a prolonged period can be tough on a muffler, so some race mufflers feature heavier-gauge steel and more durable packing materials inside.

On the other hand, weight is another big issue, so several manufacturers offer lightweight racing mufflers. Whether you sacrifice weight for durability or vice versa will depend on how close the competition is in your class--and on the size of your muffler budget.
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[Plex]

nice infor...

[Fuzz Windu]

good read