To regulate the boost pressure on turbo charged cars a wastegate is fitted to allow exhaust gases to bypass the turbine and pass straight down the exhaust down pipe. This can cause turbulent airflow around the turbine so to overcome this problem gases can be re-routed down a separate pipe about thirty centimetres long and vented straight to atmosphere. The reason for the term screamer pipe is the phenomenally loud jet engine noise they produce which is popular and highly desirable for car modifiers. Due to the noise and the fact they miss out the catalytic converter these are not technically for street use.