Summary . During engine operation, each time the exhaust valve opens, pulses of hot exhaust gases are forced into the exhaust manifold. These hot, rapidly expanding gases produce a lot of noise, some of it at very high frequency. The exhaust system does several jobs. It has to reduce the noise of the exhausting gases to acceptable levels. It has to discharge the gases safely, far enough away to prevent them re-entering the vehicle. Some of these gases are highly poisonous. In an enclosed space, carbon monoxide can cause death in minutes. It is odorless and colorless, which makes it difficult to detect, and removing it is especially important. In modern vehicles, it also keeps harmful emissions to a minimum. The exhaust system is designed to enhance engine operation. A well-designed system can improve drivability and performance. In this simplified model, burned gases exit the cylinder through the exhaust port and pass into the exhaust manifold. The first pipe is usually called the engine pipe. It is connected to the outlet of the manifold which carries the exhaust gases to the muffler, which reduces exhaust noise. Exhaust gases are then discharged through a tail pipe, usually at the rear, or sometimes, to the side or above the vehicle.