close, the external wastegate bleeds off exhaust gas from the manifold to control the boost, similar to how the actuator on a std turbo opens the poppet valve in the rear housing, bypassing the exhaust turbine, limiting the boost, on an external the screamer pipe basically vents the 'bled' gas either back into the downpipe, same a a std turbo, or into atmosphere, making the 'scream' noise as it exhausts raw unsilenced exhaust