Installing a straight pipe can potentially increase fuel consumption, especially if the lack of backpressure causes the engine to run less efficiently at lower RPMs[1]. However, the impact on fuel economy is influenced by various factors, including your driving style, engine tuning, and the specific vehicle model[1].
Some sources and user reports suggest that, under certain circumstances—often with performance modifications or highway driving—fuel economy may improve due to reduced exhaust backpressure and decreased engine strain[3][5]. But these gains are not guaranteed and results vary; in many daily driving scenarios, straight pipes tend to make negligible difference or can even reduce fuel efficiency if not properly tuned[1].
It’s also worth noting that driving habits often change after installing a straight pipe, as a louder or more aggressive exhaust note may encourage heavier acceleration, indirectly increasing fuel consumption[7]. In essence, the exhaust modification alone does not directly cause a major increase or decrease in fuel consumption—it depends largely on how the car is driven and whether the engine management system is properly adjusted for the new exhaust setup[1][7].