Change in setup - better gas mileage?

[DamnYankee]

Are mufflers need/typically used with turbo?

[ducky]

Are mufflers need/typically used with turbo?

I have stock manifolds/stock y pipe just mated to the turbo. Getting into the throttle it doesnt sound deep or throaty, has a slight tune to a glass pack, but its not that bad. At cruising my truck is reallly quiet with just the sound of the whistle, full throttle, its loud. The turbo is soooo loud