What does it mean if a turbo is t3? how do you know if a turbo is twin scroll?

 

Generally, when someone refers to a turbo as T3, it means it uses a T3 sized inlet flange for the turbine housing.

As to the question of twinscroll turbos, they don't have an open exhaust volute on the turbine housing. There is a divider that runs from the inlet to the turbine wheel, giving 2 smaller exhaust volutes.

You might try googling it, as you can probably get an easier to digest explanation.