Jaguar XJ-S V12 HE

Jaguar XJ-S V12 HE

The Jaguar XJ-S V12 HE (High Efficiency) represents a crucial evolution of Jaguar's flagship grand tourer, introducing the Michael May 'Fireball' combustion chamber technology that transformed the V12 from a fuel-guzzling extravagance into a viable luxury cruiser. The HE designation marked a turning point in the XJ-S's commercial fortune, addressing the fuel consumption criticism that had haunted the model since its 1975 launch.

The 5,343cc V12 engine in HE specification produced 299 horsepower -- a significant increase over the pre-HE version's 285 hp. More importantly, the May-Fireball cylinder head redesign, which used a unique combustion chamber shape to create a controlled swirl pattern in the fuel mixture, improved fuel efficiency by approximately 30%. This was achieved through a higher compression ratio (12.5:1 versus 10.0:1) that exploited the more complete combustion of the new head design.

The V12's character was one of the XJ-S's defining attributes. The engine was remarkably smooth, with the inherent mechanical balance of its 60-degree configuration producing a level of refinement that no six-cylinder or V8 could match. At cruising speeds, the V12 was barely audible -- only a distant, cultured murmur that spoke of unlimited reserves of power available through the slightest pressure on the throttle.

The three-speed GM Turbo-Hydramatic 400 automatic transmission was the standard (and most common) gearbox, chosen for its robust construction and smooth shifting characteristics. A four-speed manual was theoretically available but rarely specified. The automatic suited the XJ-S's grand touring character perfectly, providing seamless gear changes that complemented the V12's effortless power delivery.

The XJ-S body, designed by Malcolm Sayer shortly before his death and finalized by the Jaguar styling team, was controversial when new. The flying buttresses that framed the rear window, the angular styling, and the departure from traditional Jaguar curves divided opinion. However, the design has aged remarkably well, and the XJ-S is now recognized as one of the most distinctive and elegant British GTs of its era.

The chassis was based on the XJ6 sedan platform, providing a long wheelbase and wide track that gave the XJ-S exceptional high-speed stability. The front suspension used double wishbones with coil springs and anti-roll bar, while the rear employed Jaguar's traditional independent rear suspension with lower wishbones and fixed-length driveshafts. Power-assisted rack-and-pinion steering provided precise directional control.

Braking used ventilated discs at all four corners, with the rear discs mounted inboard adjacent to the differential -- a Jaguar tradition that reduced unsprung weight and improved ride quality. The system was servo-assisted and provided strong, progressive stopping power.

The interior was pure Jaguar luxury -- leather upholstery, wood veneer trim, deep-pile carpeting, and a comprehensive array of gauges and switches. The cabin was quiet at speed, comfortable for long journeys, and finished to a standard that justified the XJ-S's premium positioning.

The HE specification revitalized XJ-S sales, which had suffered during the fuel crises of the 1970s. With dramatically improved economy and increased power, the XJ-S V12 HE became commercially successful and remained in production, with updates, until 1996.

Today, the XJ-S V12 HE represents remarkable value in the collector market. These are genuine 150-mph grand tourers with Jaguar's legendary V12 engine, available at prices that seem almost absurdly low given their specification and capabilities.