The idea that exhaust backpressure is crucial for engine performance has shaped automotive opinions for decades. This long-held belief, however, does more harm than good. Understanding why this myth is misleading — and how it negatively impacts your engine’s performance — can make a significant difference in how you approach performance. Banks Power Dives into this long-help misconception in this video.

What Is Exhaust Backpressure?

Exhaust backpressure is the force opposing the flow of exhaust gasses from the engine cylinder to the tailpipe. Airflow resistance is present in many places such as mufflers, emissions equipment, bends in the tubing, and even ambient air.  While some have argued that a little backpressure is beneficial, the truth is that any resistance in the exhaust system takes away power that could be used for better vehicle performance.

Think of an engine as an air pump. It pulls in air during the intake stroke and pushes out exhaust gasses during the exhaust stroke. For optimal performance, this process needs as little resistance as possible. When backpressure builds up, the engine has to use more horsepower just to push those exhaust gasses out. This is called pumping loss — horsepower wasted on overcoming resistance instead of driving the vehicle. The result? Less power, poor fuel economy, and a less efficient engine.

Designing a proper exhaust is a lot trickier than it sounds. You need to size the tubing so that you don’t hurt flow by being too large, while not being so small that you introduce a restriction.

Excessive Backpressure

A less-obvious drawback caused by high backpressure is the exhaust gas getting stuck in the cylinder at the end of an exhaust stroke. That residual gas takes up some of the volume space where rich, oxygenated air can enter on the next intake phase. The next combustion cycle loses some of its power due to insufficient fresh air. That translates into reduced energy output, resulting in a corresponding decrease in your car’s performance.

Additionally, when exhaust gasses stay in the cylinder, combustion temperatures can spike, which allows for increased inefficency and even potentially damage to the engine over time. So, while some might say that a little backpressure is harmless — or even helpful — the reality is that it creates more problems than it solves.

Challenge of Turbocharged Engines

With turbocharged engines, the scenario is even worse. Those systems use exhaust gasses to turn the turbine and generate boost. This causes a giant restriction in the exhaust flow, both before and after the turbocharger. The balance between drive pressure (exhaust pressure at the inlet of the turbine) and backpressure (exhaust pressure at the outlet of the turbine) determines how effectively the turbocharger works. Excessive backpressure before or after the turbine means the engine has to exert more horsepower just to overcome that resistance. This robs the engine of potentia; power and diminishes the engine’s overall efficiency.

The Origins of the Backpressure Myth

So, where did the belief that backpressure is necessary come from? It dates back to the 1950s, when glass pack mufflers were popular. These mufflers were restrictive, but muffler shops promoted them for their sound. To address concerns about performance losses, they claimed that “a little backpressure” was beneficial. This statement took hold in car culture and has been passed down through generations, persisting even in conversations about modern vehicles.

Adding to the confusion is the concept of exhaust scavenging. Scavenging happens when exhaust pulses from one cylinder help pull gasses from another, aiding smoother flow. This process can be beneficial, especially in high-performance exhaust designs, but it is not the same as backpressure. Properly designed exhaust systems that incorporate scavenging features enhance performance without introducing the negative effects of increased backpressure. So simply running massively sized tubing isn’t the answer, either; it’s about balance: maximizing flow while minimizing restriction.

Why Reducing Backpressure Matters

Minimizing backpressure is key for better engine health and efficiency. By lowering resistance in the exhaust system, the engine doesn’t have to work as hard to push out gasses, reducing parasitic loss. This allows the vehicle to generate more power using the same amount of fuel and contributes to a longer-lasting, better-performing engine.

Moving away from the myth of necessary backpressure can help you make smarter choices for your vehicle. Putting a 3-inch exhaust on a stock 2.0-liter naturally aspirated engine makes about as much sense, performance-wise, as putting a 1.5-inch exhaust on a supercharged Hellcat engine. Forget backpressure, it’s about balance.

Banks’ new scavenging exhaust tip, as the name suggests assists in scavenging exhaust by creating a low-pressure area that helps draw the exhaust out.