The 429 Cobra Jet was available in the Mercury Cougar for exactly one model year, 1971, rated at 370 horsepower with an 11.3:1 compression ratio that made premium fuel mandatory. Pair it with a four-speed and a convertible top and the production numbers collapse to a level where registry keepers still argue over the exact figure. Mercury built a small batch in metallic blue with white tops purely for press duty. Read on for why so few buyers ever said yes.