KNOW YOUR EXHAUSTS

Once upon a time, an exhaust system just carried away waste gas from an engine. Oh, how things have changed, as our techy expert Neil explains…

Tech Talk

WORDS: NEIL ‘KNOW - IT - ALL’ CHARLTON IMAGE: FB ARCHIVE

FB: What do exhausts do?

NC: Bike exhaust systems endure a tough, thankless life. They carry violent bursts of hot (up to 7000ºC) exhaust gas away from the engine, manage pressure pulses travelling at the speed of sound, are exposed to rain, salt, flying stones and dirt and are constantly heat cycled. They also suffer considerable vibration and stress forces too.

In addition to resisting fire and brimstone, the exhaust system manages the flow of exhaust gas from the engine into the atmosphere, and somehow increases engine performance while doing so.

They also remove sound energy from the exhaust gas flow and on modern machines alter the chemical properties of the exhaust gas, reducing harmful emissions.

FB: How do they improve engine performance?

NC: Four-stroke engine exhaust systems can be specially tuned to the requirements of the engine they are fitted to. Doing so improves the flow of exhaust gas beyond what would otherwise be achieved just by allowing the gas to exit to atmosphere at the exhaust port. A tuned exhaust systems pulls off this neat trick by taking advantage of pressure pulses contained within the stream of exhaust gas. A sudden pulse of high pressure gas is introduced into an exhaust system when one of the engine’s exhaust valves is opened.