1999 Mitsubishi Eclipse tubo charger

I think you are referring to a bov? (Blow Off Valve). It is recommeded to buy an aftermarket bov to get a louder sound as you let off the gas or shift the relief of the pressure built up in the line is released through a bov and not back through the turbo. Your car is equip with a bov that dumps air back into the intake. Removing this line and plugging it would make your bov louder but will also cause the maf to make the car run like crap. Also in order to hear the turbo spool itself you would need to open the exhaust up.