The 164 was build around the 'Tipo 4' (Type 4) project.
The Type Four chassis was a common front wheel drive platform used in the 1980s for the Saab 9000, Fiat Croma, Lancia Thema and Alfa Romeo 164.
It emerged as an agreement between the four carmakers in October 1978 to reduce development costs.
The wheelbase is 2.67 m (105 inches) on all models. Because they were very similar, many parts can be exchanged between the four cars regardless of brand.
For example, the doors from the Fiat Croma fit directly on the 9000, but are lighter, due to less side impact protection.
The windshield from the Croma can also be used on the 9000. Likewise the wing mirrors off both the 9000 and the Thema are almost identical (9000 has a pressed recess on the mirror casing, Thema is without recess) and should fit both cars with the doors being similar albeit in crash structure.
Because it's platform was shared closely with three other cars, the Saab 9000's ignition key was situated on the steering column instead of between the front seats.
The design of the 164 was made by Pininfarina. Because of the fold in the car (wich also runs trough the door) the 164 only shared the chassis of the Type four.
Alfa Romeo was very glad that they could stand out with they're model. Now they could say: It's a real Alfa Romeo!