9. Corvette ZL-1
Although it was sort of a production car, the 1969 Corvette ZL1 was basically an experimental car. It came with a special, all-aluminum 427 V8 engine they designed for racing. But because they never marketed the car, most dealers never knew it was available. It looked like a stock big block 1969 Corvette, but it was far from it.
Only factory insiders and people who were well-informed of Chevrolet’s activities knew the ZL-1 even existed. However, they only produced two examples, but the rumor is that there was one more.