It's no mystery that Porsche->ke1 has built some of the most fascinating sports->ke506 and race cars->ke148 the world has seen since the late 1940s. Some of these vehicles took years to develop and had numerous prototypes that preceded them. Some of them are already famous, while Porsche kept others under wraps until the 21st century. Now, after decades of silence, the Germans are revealing their full lineup of prototypes and concept cars->ke169 in a new exhibit at the Porsche museum.

The exhibit goes by the name "Project: Secret!" and includes 14 projects Stuttgart engineers have worked on in the past. Test mules, prototypes, concept cars or plain design studies that helped the Germans develop and create the production cars we're all familiar with.

You probably recall the front-engine 924 that Porsche offered from 1976 through 1998. But did you know Porsche also built a 924-based world-record car? The project came to an abrupt halt before being finished, but the vehicle still exists. Then there's the 959 C29, an early prototype that helped Porsche engineers come up with the outstanding aerodynamic properties of the mighty 959.

Did Porsche's first sedan->ke142, the Panamera, take you by surprise when it hit the road in 2009? Then you probably don't know the company pondered the idea of a 911->ke282-based sedan from the late 1980s. That's how the 1991 Porsche 989 concept was born, a study that didn't make it to production, but end up inspiring the design of the 996-generation 911. These are just a few of the previously unknown vehicle included in the "Project: Secret!" exhibit. Watch the videos->ke278 for more intriguing prototypes the manufacturer has been hiding all these years.

One more video after the jump.