How Exhaust Systems Add Power
Exhaust systems are one of the most common entry-level performance modifications out there. Most drivers know that adding an exhaust system will help their car’s engine make more power and anyone can hear when a performance exhaust sounds great, but not as many people understand the components included in a performance exhaust system and how each of them help your engine make more power. Here is a quick explanation of the principals at work in your vehicle’s exhaust system and what each component does to take advantage of these to increase exhaust system efficiency.
As your vehicle’s engine burns fuel, exhaust gasses are produced as a byproduct and they have to be moved out of the cylinder and away from the engine. However the gasses produced are very hot and potentially harmful and they have to be properly contained. This is the exhaust system’s job. This containment of the gasses is a potential problem from the performance perspective. If pressure develops in the exhaust system, that makes it more difficult for the engine. It has to “push” harder to force the waste gasses out. This phenomenon is known as backpressure, and it is one of the primary “power robbers” in the exhaust system.
Each cylinder releases its waste gasses into the exhaust system at a different time. This job is performed by the exhaust valves. They open and close at specific times called a “firing order.” When the exhaust valve opens, it releases a sudden pulse of exhaust gas into the system, which drastically increases backpressure in the system for a short time. This is the source of the “thrumming” sound made by a car’s exhaust—the gasses exit in pulses rather than a uniform stream.
Here are some of the most common exhaust modifications and a quick explanation of how they use these principals to increase efficiency.
Exhaust headers are custom made pipes that replace the exhaust manifold on the engine. The performance increase realized when you add headers mostly has to do with management of the exhaust pulse. Headers are designed to separate the exhaust stream of the different cylinders, isolating the exhaust pulses that occur close together in the firing order. For example on a 4 cylinder car with a firing order of 1-4-3-2, the headers would join cylinder 1 with cylinder 3 and cylinder 2 with cylinder 4. This isolates the exhaust pulses away from each other in a uniform manner, increasing efficiency.
Larger Diameter Piping
Larger diameter piping allows more space for exhaust gasses to collect, and helps move them away from the engine more efficiently, reducing backpressure.
High-Flow Catalytic Converter
On most vehicles, the catalytic converter is the biggest obstruction to exhaust flow. A high flow converter helps the exhaust gasses move past this bottleneck faster, reducing backpressure.
High Flow Muffler
High performance mufflers offer an increased flow capacity over stock equipment. Although mufflers aren’t usually the most significant obstruction to the exhaust stream, an aftermarket muffler can reduce backpressure enough to free up a couple extra horsepower.