Porsche 916
Even if it looks like an ordinary, four-cylinder Porsche 914, 916 is a different animal. This special model was a rolling experiment on how to put an engine from a fantastic 911 2.7 RS into a smaller and lighter body (via Motor Trend).
The results were amazing, But Porsche feared that nobody could tame this beast or buy it since it was so expensive. In the end, the company only made 11 examples. Which are now considered the Holy Grail of the Porsche collector community.