In hopes of broadening their market appeal, Opperman built a larger mid-engined coupe with a sporty body, which they debuted at the 1958 Earl's Court Motor Show.

Compared to the Unicar, the new 'Stirling' featured things like 4-wheel independent suspension, winding windows, a 4-speed gearbox, a differential (made in-house by Opperman), and 7" hydraulic Girling drum brakes.

The added size and refinement compared to the Unicar meant extra weight, with the first car weighing approximately 900 pounds (408 kg).

Perhaps Opperman foresaw problems with having to build these 424cc motors for use in every Stirling, as the second car built featured an 'off-the-shelf' production engine; a 4-stroke, horizontally-opposed twin-cylinder unit from Austrian manufacturer Steyr-Puch, displacing 493cc and providing approximately 20 horsepower.

Unfortunately, production of the Stirling kept getting pushed back (some say due to supply issues caused by BMC, who were preparing to release their new Mini), and then later in 1959, Opperman was acquired by E.V.

The second Stirling (with the 493cc Steyr-Puch) returned from Austria a bit later, but as the company had already moved on with other projects, the car flew under the radar and avoided being destroyed.