Building horsepower for the street is a series of compromises. This is especially true when installing a muffler or a cat-back system. (For those not familiar with the term, a cat-back exhaust system is everything located behind the catalytic converter, usually consisting of tubing and the muffler.) A high-performance street muffler must do two things: flow exhaust gases as freely as possible and deaden as much sound as possible. In the past, these two goals have been at odds with each other. More flow meant more horsepower but more noise. Less noise meant a restrictive flowing muffler and a loss of horsepower. With some of today's innovative mufflers, these two may not be conflicting objectives anymore.
The advantage to a cat-back system or aftermarket muffler is that it increases horsepower and gas mileage while giving hot rods the deep throaty rumble we all love. Very few products will give you so much performance for so little money. Note, however, that while some companies claim that their mufflers "make" horsepower, what is happening in reality is the muffler is increasing the scavenging abilities of the headers or exhaust manifold. By creating a low-pressure area in the muffler, the velocity of the exhaust flow increases and this increases the scavenging in a cylinder head. Better scavenging increases the combustion efficiency of the engine and that is what increases horsepower.
There are two basic designs of mufflers. There is the straight-through design, which absorbs some sounds and has very little flow restriction. Its design consists of a perforated tube surrounded by high-temperature woven fiberglass tightly packed in a metal container. The sound energy flows through the holes in the perforated tube and the fiberglass absorbs the sound. The bigger the muffler, the more sound it can deaden. Because the airflow is straight through the muffler, there is very little backpressure to slow down the airflow. These mufflers work very well in a racing situation but they may be too loud for the street.
A chambered muffler is the second style of muffler. It has one or two pipes coming in and usually two leading out. As the name implies, there are chambers or bulkheads inside the muffler that allow the sound waves to bounce around and cancel out each other. This works very well with the higher frequency sound waves. Some companies use a perf-tube, while others use louvered tubes. The perf-tube can be designed to change the flow characteristics as well as the sound deadening ability of the muffler. The smaller and closer the holes, the better the sound deadening ability. There is generally not any sound absorption material used in a chambered muffler. This style introduces some backpressure to the exhaust system. The amount of backpressure and the rate of exhaust flow through the muffler can be varied to meet the needs of the driver.
The length of the tubes, the number and position of the holes or louvers and the position of the baffles all affect the amount of backpressure and the exhaust flow through the muffler.
It is difficult to predict how many decibels a muffler will reduce. Variables such as cam overlap and compression ratio affect noise suppression. Most muffler designs are a build it, test it, and rebuild it again process. Experience of the designer has a tremendous amount to do with the results.
Someone who has been in the exhaust system design and manufacturing arena for years is Ron Scranton at CGS Motorsports. He began designing exhaust systems in 1965. He has worked for Hedman Hedders and Jardine designing some of their systems. He spent the last two years developing CGS's new chambered muffler. It has three walls each with a single center hole to flow the exhaust gasses.
Scranton cites the importance of tuning the backpressure to the intended application. "Many of our competitors' products may work better on a race car but our stuff works best on the street," he says. "We experimented and got the right amount of backpressure for the onboard computers. On a total stock or modified stock truck, our system works well."
What about the exhaust note CGS' systems? "On the outside, you have the nice throaty sound," he adds. "They are quieter on the inside of the vehicle. We have no resonance noise inside the vehicle because of the way the louvers are placed in the pipes. Most companies use perforated tubes. We went with louvers to get rid of the resonance noise and make it quieter."
CGS uses 14-gauge aluminized piping to prevent rust and also to keep costs down. The piping is 2.5 inches in dual systems or 3 inches in single-pipe mufflers. He reports that his aluminized muffler will last as long as a stainless muffler, and comes with a lifetime warrantee. All CGS units are designed to be bolt on, and the company has custom systems for 1988 and newer trucks and SUVs.
CGS Motorsports also designed its own catalytic converter, which the company claims flows as much as 14 percent better than others on the market. How so? "We do it by putting in more precious metals," Scranton says. "It makes the converter ignite the exhaust gasses quicker so it doesn't need as much backpressure to get hot to start working. By using more precious metals, I can use bigger tubes and flow more air. Ours is a little more expensive than a stock replacement because of the extra precious metals."
Before removing the catalytic converter, keep in mind that the law says that you cannot change the converter unless it is on a vehicle that is over five years old or has more than 50,000 miles on it. If the vehicle has less than that, the original vehicle manufacturer must replace the converter when it goes bad.
When changing the system, you cannot move the oxygen sensors or the catalytic converters from the factory location. Approved aftermarket converters must mount in the exact same spot as the original converters. You cannot replace anything in front of the catalytic converter unless it is CARB approved. On new trucks, there is an oxygen sensor in front and behind the catalytic converter to check the air in and out of the converter to make sure it is working. If it is not working correctly, that annoying "check engine" warning light comes on in the dash.
