Ford had already produced successful high-performance 427 cu in and 428 cu in racing engines from older blocks, but was looking to develop one based on its newest engine family to go forward with; specifically to attempt to challenge the extremely powerful but aging Chrysler 426 Hemi in NASCAR's Grand National Division, now known as the NASCAR Cup Series.

These used the "dry-deck" method, meaning the coolant circuit for the block was separate from the cooling circuit for the head The "dry-deck" method of design is intended to strengthen the block by removing the open coolant jackets around the cylinder and reduce hot spots by providing more direct cooling.

[clarification needed] The Boss 429 engine came standard with a 735 CFM Holley 4-barrel carburetor mounted on an aluminum intake manifold that flowed well for its time.

The cars were then shipped to Kar Kraft's new assembly plant in Brighton, Michigan for engine installation and further modifications.

To help offset this, the battery was relocated to the trunk, and a 3/4" sway bar was added to the rear end to limit body roll.

So did an oil cooler which allowed both high RPM and endurance loads on the engine, and a manually controlled hood scoop for bringing in denser air for more thorough combustion.

For better ground clearance the front spoiler was made shallower than the Boss 302's, and a 3.91 ratio rear axle came with a "Traction-Lock" limited slip differential.

With the release and homologation of the extreme 440-powered Charger Daytona by rival manufacturer Dodge, the Boss 429 Mustang's NASCAR plans were scrapped.[why?]

However, as the Boss 429 engine was homologated in the Mustang, Ford used it in NASCAR until 1974 in other Ford and Mercury body platforms,[example needed] and later in NHRA Pro Stock class during the 1980's, its main proponent there being Bob Glidden's championship winning Pro Stock Thunderbird.

The rest of the car featured a very clean look that was atypical of most performance Mustangs that Ford had produced, which often emphasized appearance over its reality.

The fully functional hood scoop was body color and was noticeably larger than anything else offered on any Ford or Mercury vehicle.

[6] The huge engine, shoehorned into a modified Mustang front end, left no room for air conditioning.