Screamer pipe
A screamer pipe is a type of exhaust configuration fitted to some automotive turbocharged petrol engines with an external wastegate set-up.
Principle of Operation
To regulate the boost pressure on turbo charged engines a wastegate is fitted to allow exhaust gases to bypass the turbine and flow straight down the exhaust down pipe. This can cause turbulent airflow around the turbine and high exhaust back pressure. To overcome this problem, gases can be re-routed down a separate pipe and vented straight to atmosphere resulting in improved performance. The reason for the term screamer pipe is the phenomenally loud jet engine noise which is popular and highly desirable for car modifiers.
Limitations
By definition, this configuration allows exhaust gasses to flow straight to atmosphere. Consequently the gasses do not pass through the catalytic converter or exhaust silencer which renders it illegal for street use due noise and exhaust emission regulations in many countries. Whilst exhaust emission laws do not apply away from the public highways in most countries, many race tracks have strict noise rules in place once again outlawing screamer pipe use.