That's a pretty broad question.
Usually a single turbo will work better but twins are chosen for aesthetics or for packaging. EFI with a wide band O2 and tuning can really make a turbo setup shine, although carbs can be made to work. Going lean in any form will be disastrous to the engine. Forged pistons are recommended. Newer engines with aluminum heads and well designed combustion chambers will work much better than engines with early combustion chambers. LS style engines seem to really like forced induction.
