The Boss 429 was also built in response to Chrysler's 426 Hemi and it's success in Nascar. Ford built a 427 Hemi-headed single overhead cam motor first, but it wasn't considered stock enough for the series so along came the "semi-Hemi" head 429. Kar Kraft was given the task of wedging a 429 into the Mustang. Quarter-mile times were reported to be in the lower 14s. Although another of the hot rod magazines, Car Craft, slightly modified the stock 429 and got a 1/4 mile in the mid 12s. The street cars came from the factory with a conservative cam and a somewhat small carburetor.
Under the hood, Ford started with the 200- and 250-cubic-inch V6 motors that generate 115 and 155 horsepower, respectively. The base V8 option was a 302-cubic-inch motor that produces 220 horsepower. The big-block 390 hammers out 320, down five horsepower from the version that Ford included in the 1968 model. The top option was once again the Cobra Jet 428 that Ford conservatively rated at 335 horsepower with or without the optional ram-air induction.
2012 Ford Mustang Boss 302 Interior Design