Chevrolet Corvette ZL1
The ZL1 package was one of the best kept secrets of the late ’60s muscle car world. In fact, not many people even knew about the existence of this car. That is why they only made two. The heart of the ZL1 was the fantastic and basically racing-spec fully aluminum 427 V8. It produced up to 550 HP in mild tune.
This monster of an engine was far more powerful than anything Mopar or Ford had in production at the moment. Chevrolet produced around 200 of those engines. While most of them went to Can-Am racing teams, Chevrolet also made around 12 test Corvettes with that engine in late 1968.
The performance potential was unbelievable, so Chevrolet didn’t want to offer this wild racing engine to the public. So, they never mentioned the ZL-1 option to the press or in their official brochures. However, wealthy individuals close to the factory knew about its existence and could purchase the ZL-1.