Its just a seperate exh from the wastegate itself to vent the extra gasses after the preset boost level has been reached. i think the yanks came up with the screamer term as once the ext wastegate opens the screamer pipe is essentially an unsilenced exh
ebay has loads of screamer elbows which arent the real deal (no performance advantage) they can sound a bit pants and often bugger up the idle/low speed running of the car. only way is a proper ext wastgate imho if you want to improve performance and reduce spiking
to stop them being loud, you can re-join the screamer pipe back into the main exhaust. best bet is to rejoin minimum of 5ft from the turbo though or itll be a restriction (two lots of exh gasses squeezed into one pipe straight after the turbo)
does that make sense? does in my head, but let me know and i will try and explain better
