i guess it would depend on what class, its no more a power adder than a surercharged cobra, lighting or the other stock forced induction cars, but from what i have seen in the rule books, it really doesn't matter if it came with a turbo, its still considered a power adder, if you look in the engine section of each class it says what your allowed to have and no where i hav seen does it specify stock or aftermarket installed, so from what i have seen rule wise i would say yes its considered a power adder, might sound unfair, but rules always seem unfair
Grant