Stock vs. Replacement Exhaust Systems

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It is usually the case that automobile manufacturers are more concerned with minimizing their expenses than with providing optimal performance for the consumer when it comes to the design and production of exhaust systems. Take for instance the bends and curves of the pipes used in most stock exhaust systems. Car manufacturers use a simplistic approach called “press” bending to mold exhaust pipes; in essence a prefabricated pipe is bent to conform to a design spec. As you can tell just by bending a straw, this significantly reduces the diameter of the pipe where the bend occurs. The result is a bottleneck effect , hampering the flow of exhaust away from the engine.

In the construction of performance exhaust systems, such as the Magnaflow system, a more nuanced approach called “mandrel bending” is employed. To make certain that the pipe retains uniform diameter at the end of the molding process , a flexible rod (or mandrel) is inserted into the pipe. Thus the pipe must conform to the diameter of the mandrel even where it is bent. This is a simple idea but when combined with the other optimizations mentioned below, it makes a huge difference.

While maintaining a consistent diameter for the pipes of your exhaust system is important, so too is making sure that the chosen diameter is optimal for your auto. Again, in an effort to minimize the costs of manufacturing, auto makers use as little material as possible in the fabrication of stock exhaust systems. The result ? Pipes that are too narrow to allow for the efficient flow of exhaust. Performance exhaust systems like Magnaflow provide pipe diameters that are customized to your particular automobile. Finding the right diameter for your exhaust system together with making that diameter uniform throughout the bending process puts basic geometry to work for you and your automobile. Hooray Pythagoras!

This brings us to the concept of “engine scavenging”. Whenever a fluid or gas moves through a pipe, a vacuum is created . In particular, a vacuum is created with every explosion that occurs in a cylinder's chambers, creating a suction effect that is continuous from the moment the car is turned on until it is turned off. In the context of combustion engines, this phenomenon is called “scavenging“ and a well-designed performance exhaust systems can capitalize on it to further enhance engine efficiency.

A “manifold” is an assembly included in most stock exhaust systems, and its purpose is to accumulate the exhaust from two or more cylinder heads and merge it into one pipe for extrication. Unfortunately, this usually results in an inefficient use of engine scavenging. In the design of a high performance exhaust system, engineers create a manifold without regard to cost of manufacturing or weight but with an eye to optimizing performance. The result is a manifold that is more efficient at scavenging the exhaust from the cylinders. Performance manifolds are usually fabricated from circular steel tubing with bends and folds measured to make the paths from each cylinder's exhaust port to the common outlet all uniform in length, and joined at narrow angles to encourage pressure waves to flow through the outlet. In a set of well-tuned performance manifolds the pipe lengths are meticulously calculated to enhance exhaust flow at a particular engine rpm. It is precisely this configuration of manifolds that allows performance exhaust systems to harness the power of engine scavenging.

Exhaust Tips

No performance exhaust system would be complete without a classy , eye-catching exhaust tip. While aesthetics are a major motivation behind one's choice of exhaust tip (or the decision to have one at all) , they can in fact serve as a functional part of a performance exhaust system. The tip is usually made of chrome (or chrome-plated) and is often of a larger diameter than the pipes in the rest of the exhaust system. This variance in diameter produces a final reduction in exhaust pressure.

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Truck Champ's Exhaust Systems Learning Center

(back to main Exhaust System page)

• What Is An Exhaust System?
• More Exhaust System Information
• Stock Vs. Performance Replacement Exhaust System