After setting the wheels in motion by fitting a V8 engine in an  AC Ace to create the first Shelby Cobra Series, the 260-289, Carl Shelby set the wire a lot higher with the launch of the 427, an eminently more powerful vehicle.

The reasoning behind the upgrade was that AC and Shelby had reached the mutual conclusion that they had no means to increase the power of the racing 289s without seriously compromising reliability. 

Eventually, the decision was reached to fit a more the 7-litre (427 cu in) big-block V8 engine, the same as currently installed in Ford's  Galaxie NASCAR racer to leave the opposition in their wake.

TheCobra 427's massive engine was matched up to a manual 4-speed gearbox.

For the faint of heart, AC also offered Ford three-speed automatic transmission.

AC used an updated version of the parallel tube concept for the 427 chassis, a system  first used on the updated (Mark III) Shelby Cobra, although this time longer and designed to provide a smoother and softer ride.

More so than any of its predecessors, construction on the 427 was a multi-step process, with the engine arriving from Michigan; placed in a chassis in Britain; body added and final assembly undertaken in Italy; then back to Britain for testing and inspection.

When everything was in place, prior to its commercial release,  AC  handed the opposition, in particular Aston Martin, a rapid wake up call that the 427 was coming, setting the benchmark for performance by accelerating from 0-161km/h (100mph) then back down to a standstill in just 13.8 seconds- almost half the time that any of their rivals in the sector had achieved.

Confident in the 427’s abilities, AC presented a prototype version at the London Motor Show in late 1965, with production beginning during 1966.

The styling of the new drophead coupe was markedly different from the original  Ace or the other Cobra Shelby models, although once again a two-seater body, this time designed and created by the legendary Turin coachbuilders Frua.

The 427 bore a remarkable resemblance to Maserati's Mistral (not too surprising as Frua also designed it) was characterised by its low, flat grille, with wraparound parking lights below the headlamps.

The vehicle's body was idrntical to that of the Cobra 289, apart from its massively flared wheel arches, neccessary to accommodate the 427's wider track and oversized wheels.

Media response to the new Cobra 427 was overwhelming, with magazine sponsored road tests instantly categorising it as " a fearsome and single-minded machine".

Despite the intitial excitement, it soon transpired that the AC Shelby Cobra 427 was too rich for most people's blood, causing sales to be well below expectations.

TheAC Shelby Cobra 427 Frua continued in production, although with numbers steadily dwindling until October 1966 when AC replaced it with the slightly more conservative, but no less powerful 428.