The catalytic converter became mandatory automotive equipment in 1981. Some drivers choose to remove the pollution-preventing device in favor of a straight pipe that installs into the catalytic converter's location but offers no environmental benefits. This is called a "test pipe."
A test pipe replaces an automobile's catalytic converter. Whereas a catalytic converter changes some of a car's toxic exhaust into harmless gases, a test pipe lets pollutants in the exhaust flow straight out of the tailpipe.
Power-hungry drivers install test pipes to increase horsepower. Catalytic converters restrict exhaust flow, which reduces horsepower. Test pipes don't contain the honeycomb of reactive that purifies harmful exhausts, so they don't restrict exhaust flow. They actually increase horsepower.
Operating a vehicle without a catalytic converter breaks the law. Drivers in the United States can not legally remove their cars' catalytic converters. Using a test pipe also allows more harmful emissions to enter the atmosphere.
