At speeds above 100mph, the Ghia exhibits visible nose (and therefore axle) lift, translating to oversensitivity in the steering, and it generates enough rear axle lift and overall aero drag to be a factor. Now that we are running for top end, this matters. With 150 hp, we can run a theoretical 153 mph with a 3.78 r&p and stock gearing, which means a practical 140 mph.

Porsche began paying serious attention to aerodynamics for its road cars in the 1974 911 2.7 Carrera with its now-famous "ducktail" jutting up off the engine lid, and a specially designed front bumper "chin" spoiler.

The ducktail and chin spoiler did not add downforce, but reduced lift. The ducktail alone kept the rear well planted at speed by reducing rear lift by about 70%. It also improved airflow through the engine-cover grille and moved the effective center of pressure about six inches rearward as another aid to stability.

The center of pressure should be behind the center of gravity for stability. A car tries to rotate at its center of gravity. The center of pressure is the point on the side of a vehicle where wind most affects the car to make it rotate.

Porsche's wind tunnel tests indicated that the front spoiler and rear ducktail did not increase the car's top speed, but it didn't slow it down, and the common 911 nervousness at top end was conquered.

Taking advantage of Porsche's research, RetroRacing replicated the ducktail exactly, but instead of the short steet-practical chin spoiler, now runs a tarmac-scraping airdam copied from the Porsche 934 series.

Previous tests are below please click on the link to view them.