The XK140 and XK150

On the roadster and drophead cars the bulkhead was moved forward 76 mm (3 in) to give more room in the cockpit; on the fixed-head coupe the bulkhead was reshaped to give a similar effect without changing the roof pressing, although the roofline was raised 25 mm (1 in) to heighten the impression of airiness in the cockpit. The extra space liberated in the drophead (which also had a 25 mm-1 in-higher hood) and fixed-head coupes was used for two tiny rear seats, which made the cars more appealing to families with small children, At a pinch, an adult could squeeze in the back across the seats for short journeys.

The XK140, which was introduced in October 1954, was easily identified because it had similar bumpers (fenders) to the Mark VII saloon, a development that gave better protection against clumsy parkers, and a different radiator grille with a new cooling system, following complaints about overheating in traffic. It was also a better car mechanically. The special-equipment XK120's engine was used as standard on all XK140s, with a single exhaust to give 180 bhp, or with a high-compression C type head and twin exhausts to give 210 bhp. The standard XK140 was called the XK140M in the United States (because of its 'modified' engine) and the XK140 with a C type head, the XK140MC, following similar, but unofficial, designations given to export XK120s, A close-ratio gearbox, which had been available as an option on XK120s since 1953, was now standardized, and more cars left the factory with wire wheels.

This range continued virtually unchanged until October 1956 as the factory concentrated on introducing the Mark I saloon (described in the chapter 'The Businessman's Express') and revising the Mark VII. It was at this point that automatic transmission like that offered on the Mark VII became available as an option on the drophead and fixed-head coupes.

Soon after, in May 1957, the XK was revised dramatically for the last time, as the XK150. The XK150, introduced at first in drophead and fixed-head forms, was as near as you could get to an XK saloon. It was bigger and heavier, but a good deal faster in the middle range of its performance because it was fitted with a new B type cylinder head. This developed only 190 bhp but gave the engine a lot more torque in mid-range. The C type head was still available for ultimate top-end performance and the original head became known as the A type. Almost as soon as the XK150 went into production, following considerable difficulties with a factory fire, it was fitted with disc brakes all round which-like the C type on which they had been pioneered-made the new car far faster from point to point.

The chassis and running gear of the XK150 were substantially the same as on the XK140, but the coachwork looked very different. The body was given a raised waistline with bulbous doors and wings to allow the interior to be widened by 102 mm (4 in). This gave the passengers more room; and they also benefited from a further raising of the scuttle line. A wrap -around windscreen was fitted now that glass of the right quality was available and the fixed-head coupe was given a large saloon-style rear window to make it feel more spacious and airy. Other body changes included wrapping the rear bumper around the flanks for greater protection and fitting a wider radiator grille to improve cooling further. The fixed-head and drophead coupes shared a similar interior but the XK150 roadster was far more spartan. This variant was not introduced until March 1958 because the factory was still recovering from the fire, and to have launched it earlier would have added complications to already stretched resources. Naturally this was a faster car because it was lighter and it became even quicker when it was fitted with an optional straight--port cylinder head and triple carburettors, which increased the power to 250 bhp. In this form it was known as the XK150S. The brakes were improved at the same time by fitting square quick-change pads developed on the D type, in place of the older round type. At this point, wire wheels were fitted as standard on the special-equipment models and overdrive on the XK150s, which was not available with the option of an automatic gearbox: this was because it was intended primarily as a competition car. The S type options were made available on the fixed-head coupe from February 1959, but not on the drophead at first because it was intended purely as a touring car.

The 3.8-litre XK150’s

Then, in October 1959, an enlarged engine was offered to provide even
more power and torque, This was the 3.8-litre unit which became available on all XK models; it had been under development by the factory since it was first used on a D type in 1956, The factory's version of the 3.8-litre XK unit was considerably different to what had been achieved by people such as Phil Hill. Jaguar stepped up the capacity of the factory engine to 3781 cc by increasing the bore to 87 mm in a new block with dry liners, rather than by boring out the existing 3.4-litre block, which had proved risky.

In this form, with a gold-painted 9:1 compression ratio straight-port cylinder head and triple SU carburettors, the XK150s 3.8-litre, as it was called, produced 265 bhp; with a blue-painted B type 9:1 compression head and twin SUs, it turned out 220 bhp with drops of about 10 bhp each for the 8:1 and 7:1 versions of this head, The lower compression ratios were normally used in export markets where only poor quality fuel was available, These cylinder head and carburettor options were also available on the 3.4-litre range, which was retained, giving a seemingly endless variety of power units. In these forms the Jaguar XK sports cars continued in production until the end of 1960, when they were discontinued to make way for the sensational new E type.