[MetroMPG]

Every once in a while, GM has shown it's capable of hitting one out of the park, aerodynamically speaking. Unfortunately, this one never saw North American roads.

Here's a pic of the Opel / Vauxhall / Holden Calibra, for those who don't know it:

Launched in 1989, it was designed by an American who headed GM design in Europe. At the time, it was apparently the most aerodynamic production car available anywhere. (Source: Wikipedia)

Obviously they started with a decent shape.

But the designers paid a lot of attention to optimizing the details as well, such as the grille openings: only the 8-valve version of the car had the Cd 0.26 figure - the 16v engine needed more cooling, which meant a bigger hole in the front, and a worse Cd of 0.29 (other contributors to the change were probably things like wider tires, chunky rims, etc).

Here's another line about the small and sometimes counter-intuitive details that the Calibra engineers dealt with:

In the case of the Calibra, the centre section of the front spoiler was lifted to allow more (yes more!) air to flow under the middle of the car, so making the total flow more parallel with the car’s long axis. This reduced the amount of air being deflected outwards by the front wheels, reducing the size of the wake and so drag.
(Source: Modifying Under-Car Airflow, Part 1)

This YouTube vid contains a bit more of a look into what makes the car slippery:

Some points made in the vid:

• obvious attention to boat tailing/tear drop shape
• side skirts
• continuous front contour, from hood, to lights, to bumper, to front undertray

And an interesting quote:

One serious shortcoming is ventilation. Like many streamlined cars there's no through-flow of air, and the only way to get that is to have the fan on full almost all the time.

These sloping windscreens also allow an awful lot of sunlight in here and it gets very hot & stuffy.

The reviewer also notes that the sharply raked A pillars make ingress/egress more difficult. (My observation: they also affect outward visibility.)

One design issue that was out of place on the slick Calibra was an outward opening sunroof (the kind that slides on top of the roof, rather than inside). In the open position, it would destroy the car's Cd.