The XK140 was introduced in late 1954 and sold as a 1955 model. The primary visual change was the more substantial front and rear bumpers, with large over riders. Another new feature was modern flashing turn signals, operated by a separate switch on the dash. The twin amber lights positioned above the front bumper helped to distinguish the XK140 – until XK120 owners started installing the same equipment.

Front grille size stayed the same but became a one piece cast unit with fewer, thicker vertical slats. The Jaguar badge was fitted to the grille itself, rather than being mounted between the grille and hood/bonnet as on the XK-120. A chrome trim strip extended back over the bonnet and at the rear continued down the centre of the boot (trunk) lid, where it contained a red shield with the words "Winner Le Mans 1951–3" inscribed in gold.

The interior was improved for taller drivers with an addition of 3 inches (76 mm) of legroom, as a result of relocating the engine, firewall and dash forward. The new arrangement left no room for the XK120 battery compartment, and the single battery was now located low down inside the wing on the inlet side, making it almost impossible to replace.

The XK140 continued to feature the famous Jaguar XK engine with the Special Equipment modifications from the XK120 as standard, increasing the specified power by 10 bhp to 190 bhp (142 kW) gross at 5500 rpm. The special C-Type cylinder head was also carried through from the XK120 catalogue as an option, specified at 210 bhp (157 kW) gross at 5750 rpm.

A car fitted with the C-type cylinder head, 2-inch sand-cast H8 carburetors, heavier front torsion bars and twin exhaust pipes was known in the UK as an XK-140 SE. In North America it was popularly called an XK-140 MC.

In 1956 the XK140 became the first Jaguar sports car to be offered with an automatic transmission. As with the XK120, wire wheels and dual exhausts were options, although most cars imported into the United States had wire wheels. Cars with disc wheels continued to be offered with fender skirts (spats) closing the rear wheel arch.

The XK140 was available in three body styles. The OTS (Open Two Sweater) roadster had a light canvas top assembly that when lowered fitted behind the seats and thus completely disappeared inside the body. The interior of the OTS was trimmed in leather and leatherette, including the dash. Like the XK120 Roadster, the XK140 OTS had removable canvas and plastic side curtains on light alloy doors, and either a long or short tonneau cover to keep the cockpit dry with the top down.

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