Ford Big Blocks

Everything about the 1971, 1972 & 1973 Ford Mustang

429 Big Block

The late ’60s is overflowing with tales of “What if?” For one, what if the post-war momentum in American performance hadn’t been challenged by anything other than the next-fastest car? Well, then the early ’70s came. It was a time when the oil crisis, government regulators, and insurance agencies drowned out the voices of racing teams. Manufacturers didn’t know how to react other than to drop everything and restart. For fans of Ford’s 429-cubic-inch performance V-8, a lot of what-ifs persist surrounding this engine whose flame burned to its full brightness for only a short spell. On this day of April 29 (4/29), we think it deserves some recognition.

For Ford, the 429s it produced from 1968–73 for its next generation of big-block power were visible victims of this rapid change in direction. These engines benefited significantly from new casting procedures, which helped to drop weight compared to the outgoing Ford-Edsel big-blocks. Since its days as the king of flatheads, the Blue Oval had been studying its cross-town rivals over at GM and Chrysler; Ford began experimenting with advanced overhead cams and other exotic tricks in Indy car, and the new 385 family of big-blocks looked like they would continue the innovative traditions of their forefathers. It was never meant to be, however. Ford would ultimately kill high-performance big-blocks by 1974, leaving the brand’s trucks and full-size sedans—which used the longer-stroke 460 until 1997—as the last bastions of the big-inch legacy.

Cobra Jet:

Cobra Jet 429
Photo by Colin Comer

In 1968, the 429 superseded the 427 as Ford’s premier big-block, replacing the heavier FE-series. This new 385 series, dubbed the Lima, served a wide array of luxury sedan pickups thanks to its brute force at low rpm. These more pedestrian uses for big-blocks were great for the high-performance divisions, too. It gave them an abundant source of big-displacement foundations upon which to build. While most of the big-blocks churned out of Lima, Ohio, were the sorts of things you’d find humming under the hood of a Lincoln Mark III, a select few would slide down another assembly line to be born as Cobra Jets.

With a 4.36-inch bore and shorter 3.59-inch stroke than the 460, the 429-cu-in Cobra Jet promised at least 370 hp thanks to its snappy 11.3:1 compression ratio, and it became the go-to power plant for the late-’60s Fords. You could get a Cobra Jet, with or without a shaker hood scoop, in everything from the Cougar to the Ranchero, and it was the last big-block performance offered in a Ford car as the pressure from insurance agencies and government regulators began to end OEM involvement in motorsports. By 1972, the Cobra Jet had fallen off the ordering sheets as Ford prepared to enter a decade of despair and neutered performance.

The Boss:

Boss 429 Engine
Photo by Colin Comer

If the loss of the Cobra Jet wasn’t tragic enough, the Boss 429 was a truly unfortunate victim of being at the right place at the wrong time. Conceived for production as a justifiable expense of hewing to NASCAR homologation rules, the weapons-grade dominators dropped into the Mustang by Kar Kraft were possibly the peak of the “Win on Sunday, Sell on Monday” mentality among Ford’s racing efforts in the period. Building upon wisdom that was honed through countless laps in the pursuit of speed, Ford threw its engineering might at the 429 to give it one last hoorah in stock car racing, where the big-port Hemis were continually trouncing the field. Unleashed for the Boss was a mammoth big-block with canted valves, hemispherical combustion chambers, and enough port volume swallow an oil tanker. Learning its lesson from the 427 SOHC mishap back in ’66 (when the engine wasn’t properly homologated and became a massive investment loss when NASCAR banned it), Ford met the required production numbers for the almighty Mustang Boss 429’s engine to be eligible into NASCAR competition, selling 859 units in 1969 and 499 in the following year. Notably, two Mercury Cougars were equipped with the Boss 429, sold respectively to “Dyno Don” Nicholson and “Fast Freddie” Schartman for the princely sum of $1.

Boss 429 Ad Ford
Photo by Ford

Due to the placement of canted exhaust valves, which ease the angle at which the exhaust gasses must turn in order to escape the head compared to a traditional wedge design, the Boss’ cylinder head itself was massive. It provided a few packaging challenges, especially in light of Ford’s decision to solicit Kar Kraft to place the wide-shouldered beast between the strut towers of the compact Mustang. Kar Kraft had to modify the Mustang’s strut towers and front suspension to allow for the necessary additional berth. The result, the Mustang Boss 429, was a nose-heavy brute sold to dealers with the claims of a modest 375 hp. The truth? These were barely-detuned NASCAR engines.

With the laser focus Ford was applying to motorsports at the close of the 1960s, we wonder what could’ve happened if the 429 had the privilege of continued development. While it served well with Ford’s Torino and Mercury’s Cyclone in NASCAR, earning some success in the NHRA Super Stock with the Boss 429 Mustangs, the new big-block never experienced the continual development and persistent polish that the venerable FEs did, despite showing exceptional promise. And on that high water mark, we salute the 429. 2020