"they claim the OEM spoiler won't have any effect on the down force"
Well, it kinda does or not, depending on just how it is designed. Basically what these small spoilers can do is retard the turbulent airflow behind the rear of the car from climbing back up onto what would be the trunk area, if it had one. This encourages the airflow over the top of the car to remain attached further down behind, like a tailored Kamm effect, reducing drag a little and increasing high speed stability.
Remember the early pre-facelift Audi TT roadster, where they found that they had to end up adding a small spoiler on the aft end in order to decrease high speed instability, and reduce drag just a little as well.
I'm sure that this 4C car design, as I'm sure the new Giulia, was wind tunnel tested with and without the spoiler to determine the effect, and I'm inclined to believe that it is for the above purpose. Not big enough or in the proper position to produce downforce, but just enough to reduce drag inducing trunk reversed airflow.
A spoiler as mounted on the 164S however, may have less of an effect, as it has that slot below it allowing some turbulent air to flow up and forward onto the trunk lid, so I suspect that it is more for visual effects, not aero, but Alfa did mention somewhere that the 164S fairings, ie, 'aero package', did reduce the vehicle drag coefficient just a little, although it is mostly for visual effect. IMO.
89 Milano (wife's daily driver since 1989, Shankle Sport)
91 164S (my daily driver since 1994)
94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)
previously owned since 1964:
62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
Last edited by Del; 01-06-2017 at 07:51 PM.