Automotive  

Free-flowing exhaust systems may maximize peak horsepower; this is typically accomplished by making the path as straight as possible, using a consistent diameter throughout the system and eliminating obstacles such as catalytic converters and pre-catalytic converters or by replacing the muffler with a less restrictive (and usually louder) one. In a normally-aspirated engine, this may result in the use of oversized piping which may negatively affect low-end torque. (Forced induction engines are not as susceptible to this side effect). Furthermore, eliminating catalytic converters and other emissions control hardware will often render the vehicle illegal for street use in many jurisdictions. Another thing you may do to get a little more power out of your engine is the installation of an electric or basic cable activated exhaust cutout. This opens the exhaust either before the catalytic converter or after. Catalytic converters are the objects that clean your exhaust as it leaves the motor, so putting these cutouts before the catalytic converter may be illegal, because the exhaust coming out of them isn’t being cleaned. If you place them after the catalytic converter, as in before the mufflers, it may be legal (depending in jurisdiction) because the exhaust is already cleaned as it escapes. Doing this in most cars may improve your horsepower.

The piping that connects all of the individual components of the exhaust system is called the exhaust pipe. Contrary to popular belief, the largest diameter exhaust pipe is not always better. If the pipe is too large, the scavenging effect will suffer at low rpm, resulting in loss of torque and drivability. Running a pipe that is too large may also decrease a car’s ground clearance, increasing the risk of the exhaust being damaged when the car moves over an uneven surface.