 |  | | | If you think of your vehicle's engine as basically a big pump, the need for free-flowing exhausts becomes obvious. Air in, air out—that's what it's all about.
Factory Flow | Back To Top
Your engine takes air in through the intake system, mixes it with fuel, compresses the gases, ignites the gases, and passes the combustion byproducts out the tailpipe. Sounds simple enough, but the economics of mass-production and other concerns don't always allow for optimum design of the exhaust headers. Factory exhaust systems, usually made of cast iron, are a matter of compromise. Performance is important, but so is noise control. While high-performance enthusiasts live for the sound of rumbling exhausts, the average consumer feels less is more when in comes to exhaust noise. Factory cast-iron exhaust manifolds are quiet, plus they are inexpensive, easy to install and remove, and usually outlast the engine.
The downside is that the design of most cast-iron exhaust manifolds isn't especially free flowing. That contributes to backpressure, which impedes performance. Cast-iron exhaust manifolds are also big heat sinks, retaining a lot of exhaust heat right next to the cylinder heads, which isn't good for the rapid evacuation of exhaust gases.
As mentioned at the outset, the principles behind a good exhaust system are fairly basic. When exhaust gases flow out of the cylinder heads and then progress through the system, they cool and contract as they go. The goal is to get exhaust out of the system as quickly and thoroughly as possible—greater heat dissipation allows the engine to run cooler, and less exhaust in the cylinders allows more fresh air in for a better burn.
Upgrade Benefits | Back To Top
Exhaust headers are the first link in the performance-exhaust chain, and manufacturers claim that these can add as much as 40 more usable horsepower. Aftermarket exhausts don't actually make horsepower, but they do choke off less power by reducing backpressure for better flow. To improve performance, a set of performance headers typically has thinner walls and a smoother inside finish. Not only that, custom exhaust headers look way cooler, especially when chromed or coated. Thermal-barrier coatings can improve heat dissipation on headers and exhaust components. These coatings contain either aluminum or ceramic fragments that are either baked on or electro-statically applied. In addition to improving exhaust flow, a thermal coating can also reduce heat soaking of a sensitive component such as a starter motor, which might cause it to otherwise malfunction.
While the ideal situation is to have equal-length exhaust tubes, even a set of aftermarket headers has to strike a compromise between length of the primary tubes and fitting in the engine compartment. In addition, the so-called Shorty headers are more adaptable to a wider range of applications.
Consistency of diameter is another advantage of aftermarket headers. Most OEM applications and franchise muffler shops use press bends, which constrict the inner diameter at the radii. Almost all aftermarket systems use ball-mandrel bends, which maintain a constant inner diameter at the bends for less restricted flow.
Proper Setup | Back To Top
Due to these design differences, upgrading your exhaust system is one of easiest ways to make impressive horsepower and torque gains. You can also spend a lot of money adding parts that do little or nothing to increase power. In exhaust systems, bigger is not always better. The best exhaust system is one that is ideally matched to the engine and how your vehicle is most often used. It doesn't make any sense to tune for high rpm or top-end speed if you spend most of your time towing a heavy trailer or sloshing through mud bogs.
It's important to strike a balance between increasing exhaust gas velocity and having a pipe diameter that's sufficient to extract the gases. A smaller diameter header can boost exhaust gas speed at low rpm (great for hill-climbing torque), but can become restrictive at high rpm. This situation is more critical in a sports car than a 4x4. As long as you realize where your headers work best and match that to your most common driving situations, you should be happy. You can find several different header designs for the same engine.
Installation | Back To Top
As shown in the installation photos on this '02 Chevy Suburban, bolting on a new set of headers may not be as easy as it might sound. Accessing header bolts can be a real pain near tight-radius tubes. You may need to buy some special tools because there are special small head bolts in six-sided, twelve-sided, and Allen-head configurations. Also, be prepared to remove some other components such as the steering shaft in order to remove the stock headers and squeeze in the new ones. Don't let any of that deter you, though, because once you've installed a new set of exhaust headers, you should immediately notice a big improvement in your vehicle's performance.
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