Sadly, two of the most enticing V16 engines never made it to production. In 1987, BMW engine development boss Karlheinz Lange had his team graft two extra cylinders onto each bank of their existing V12, making a 402-horsepower V16. The next year, the carmaker dropped that 6.7-liter engine in an E32 series 750iL, cutting vents in the rear fenders to feed air to the radiator, which had been moved to the trunk to make room for the extra four cylinders. 

The gill-like cutouts gave the prototype the nickname “Goldfisch” (goldfish), but it was flushed by BMW before it saw a showroom. In 2003, Cadillac paid homage to its V16 past with the Sixteen concept car, a 5,000-pound behemoth with a 13.6-liter V16 capable of 1,000 horsepower and 1,000 pound-feet of torque. That engine featured a now-common technology that deactivates cylinders when they’re not needed, and the car now lives at the Audrain Auto Museum in Newport, Rhode Island.

A few other cars with V16s never really got rolling. The Cizeta-Moroder V16T actually went into production briefly in 1991, but only about 10 were made before Cizeta went under. Around the time BMW and Cizeta were working on their V16s, Mercedes-Benz also reportedly built about 85 prototype cars with V16 engines. Finally, Rolls-Royce made the V16-powered 100EX in 2004, but that car was an experimental model built solely as a test platform for new systems.