2007 Publications International Ltd.
1986 Jaguar XJ6 Chassis and Engine
The 1986 Jaguar XJ6's design process focused on preserving reliability and "Jaguarness." However, as U.S. buyers equated “Jaguarness” with sloppy workmanship and poor reliability, the XJ40 was designed for greater simplicity and thus superior manufacturing quality than was possible with the Series III’s mid-Sixties engineering. For example, it employed 25 percent fewer body stampings, which implied more consistent assembly, and there was a new electrical system with one-way connectors, seven microprocessors, and low-current ground-line switching, all of it said to be aircraft-reliable.
Better fuel economy was also deemed important but, again, not at the expense of “Jaguarness.” The new XJ6 thus weighed only some 100-160 pounds less than Series III, most of it accounted for by the new all-aluminum AJ6 engine. It was a 3.6-liter dohc six with four valves per cylinder, which got its initial shakedown in European XJ-S coupes and cabriolets from 1983. Wheelbase was unchanged at 113 inches, but overall width was a whopping 9.3 inches greater. Despite that, and the unfashionably square lower-body styling, the claimed drag coefficient dropped from 0.44 to 0.37, hardly an astonishing figure nowadays but a creditable reduction.
More significant for economy-minded Americans was the switch from three-speed automatic to a more efficient four-speed overdrive transmission with locking converter clutch, ZF’s excellent 4HP22 unit. And Jaguar added a literal twist in the novel “J-gate” selector, which put the 2nd- and 3rd-gear slots in a separate, left plane for easier manual use. Alas, those who’d prefer manual shift would have had to move to Europe or Japan, where Jaguar offered a five-speed overdrive unit from Getrag.
Still, the AJ6 was definitely more efficient than the old XK engine, thanks partly to integrated Lucas/Bosch electronic ignition/port fuel injection. The initial U.S. version delivered fractionally more power and torque than the last 4.2 XK, resulting in a slightly better power-to-weight ratio (21.9 lbs/horsepower versus 23.1). Even so, its 181 horsepower was a whopping 37 horsepower less the European engine’s, which prompted a hasty compression increase (from 8.0 to 9.6:1) during 1987 that added another 14 horsepower and 11 pounds-feet torque. A further aid to performance appeared for 1989 in a final drive ratio shortened from the original long-striding 2.88:1 to a livelier 3.58:1.
Go to the next page to read about features and specifications for the updated Jaguar XJ6.