The KR-8 earned nationwide fame when it was featured in Hot Rod magazine, and from that point on, Mustang enthusiasts from all corners of the country started flooding local dealerships, enquiring about the availability of a similar engine setup. Some even went as far as tearing up the article from the magazine and mailing it to Ford's headquarters, demainding the powerplant.
In April 1968, the Blue Oval obliged, introducing a factory-built 428 inspired by the Tasca Ford units and called it Cobra Jet.
The engine (in both Cobra Jet and Super Cobra Jet configurations) was built on a regular production line and used different heads throughout its lifespan, but the output rating remained the same: 335 hp and 440 lb-ft (600 Nm).
It turned the Mustang and Cougar pony cars into veritable supercars but also powered intermediates such as the Torino, Fairlane, Comet, or Cyclone.
5. 1969 Mercury Cyclone Cobra Jet
Apart from the high-powered engine that gave it its name, the Cyclone Cobra Jet was available with bespoke hood stripes, a blacked-out grille, dual exhausts, a competition handling package, a 3:50:1 rear axle ratio, and an optional Ram Air intake.
Though it had a slight weight disadvantage over its CJ-powered pony car sibling (the Cougar), the Mercury Cyclone CJ was slightly faster for that model year.
In a test conducted by Motor Trend, the intermediate fastback was able to run the quarter mile in 13.86 seconds at 101.7 mph (163.6 kph). In contrast, the 1969 CJ-powered Mercury Cougar Eliminator's fastest independently-tested run (courtesy of Supercar Annual) yielded a time of 13.90 seconds. Not a huge difference by any means, but still enough to make the 1969 Cyclone faster.
4. 1968 Mercury 428 Cyclone GT
As I mentioned earlier, the Cyclone became its own model in 1968, receiving a thorough redesign that differentiated it from its Mercury Comet and Ford Fairlane siblings.
The high-performance trim was the GT which came with a 390-ci (6.4 liters) V8 as standard, but by mid-model year the newly-introduced Cobra Jet 428 became an option, replacing the old 427. Only some of the 1968 GTs got this option, and even fewer have survived.
The 3,740-pound (1,696 kg) 428 Cyclone GT was not the fastest muscle car around in 1968, but with a quarter mile run of 13.85 seconds at 101.69 mph (163.6 kph), it was the fourth fastest factory model ever powered by the Cobra Jet.
3. 1969 Ford Mustang Mach 1 428 Cobra Jet
However, even when equipped with the most powerful V8 option, it was far from a performance car. That started to change from 1965 onwards when Ford (initially with the help of Shelby American) began adding more power to the engine lineup.
For the 1969 model year, the whole Mustang lineup received another set of both cosmetic and mechanical improvements. That year also marked the introduction of a series of high-performance models, including the popular Mach 1.
Instantly recognizable due to its partially black hood and complementing side strips, the Mach 1 was only available as a SportsRoof (fastback) and came standard with a multitude of performance features. Its options list also included the 428 CJ engine, which transformed it into one of the most badass pony cars that one could buy that year.
Equipped with this engine, the Mach 1 'Stang ran the quarter mile in 13.69 seconds at a speed of 103.4 mph (166.4 kph) during a run by Popular Hot Rodding magazine.
2. 1968 Ford Mustang 428 Cobra Jet
Ford also built 50 CJ-powered 'Stangs (dubbed 135 Series) for NHRA stock class homologation and shipped them to select dealerships nationwide.
Compared to 1969, when anyone could get a CJ-powered Mach 1 in a bunch of available colors, only a chosen few could get one in 1968, and they had to settle for one color: Wimbledon White.
The folks at Hot Rod magazine got their hands on one and achieved a quarter-mile time of 13.56 seconds at 106.6 mph (171.5 kph).
1. 1968 Mercury Cougar GT-E 428 CJ
For the 1968 model year, a new high-performance version called GT-E was introduced. Initially, it could be had with the mighty 427, but the Cobra Jet became its sole engine option from April onwards.
Those who wanted to have the ultimate version of the Cougar also added the XR-7 package (shown above), which brought a wood-trimmed dashboard, full instrumentation with black-face gauges, toggle switches, and an overhead console.
The Cougar GT-E 428 CJ was capable of running the quarter mile in 13.23 seconds at 103.4 mph (166.4 kph). Not only was it the fastest factory-built, Cobra-Jet powered model, but, according to Super Stock & Drag Illustrated magazine, it was the fastest muscle car of 1968.