The 5,344cc V12 arrived in the XJ in 1972 and ran to 1992, with a 6.0 litre (5,993cc) from 1992. Everything else about the car is XJ — fully independent suspension, disc brakes all round with the rears inboard, twin fuel tanks — so the series identification and the body-rubber breakpoints on the XJ6 page all apply here too, including the big one: the Series 3 of April 1979 has bonded screens and no opening front quarter-light. What is specific to the V12 is fuelling and ignition. Four side-draught Zenith-Stromberg carburettors initially; Bosch D-Jetronic fuel injection under Lucas licence from April 1975, which the factory records pin to engine number 7P 25001; and the HE from 1981, with Michael May’s high-swirl heads, compression up to 12.5:1 and roughly fifty per cent better economy.
The ignition changed three times. Lucas OPUS from 1971, Constant Energy Ignition from 1982, and Magneti Marelli from mid-1989. Three systems across one engine family, so establish the year before ordering anything electrical. The Daimler Double-Six is an XJ12 — the name revives Daimler’s own 1926–38 V12, but the car is badging and trim over a Jaguar V12, and the parts are XJ12 parts. Production: 14,226 V12s in the Series 2 and 10,500 in the Series 3, with the V12 continuing after six-cylinder production ended in 1986/87. 161,583 V12 engines were built in total, also going into the E-Type Series 3, the XJ-S and the Panther J.72 and De Ville.
Jaguar XJ12 — specification & changes within the model
- The engine
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5,344cc V12, 1971–1997, 161,583 built. 6.0 litre (5,993cc) from 1992, stroked to 78.5mm.
- Fuelling — the April 1975 breakpoint
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Four side-draught Zenith-Stromberg carburettors initially. Bosch D-Jetronic fuel injection under Lucas licence from April 1975 — the factory reference pins it to engine number 7P 25001.
- Ignition — three systems
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Lucas OPUS from 1971 · Constant Energy Ignition from 1982 · Magneti Marelli from mid-1989. Establish the year before ordering.
- The HE, 1981
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Michael May high-swirl heads with swirl chambers and dished pistons, compression from 10.5:1 to 12.5:1, and roughly fifty per cent better economy.
- The Daimler Double-Six is this car
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Badging and trim only. The name revives Daimler’s own 1926–38 V12, but mechanically a Double-Six is an XJ12 and takes XJ12 parts. Cross-reference here.
- Body and glass — the XJ rules apply
- Series identification and every body-rubber breakpoint are as on the XJ6, including bonded screens and the deleted front quarter-light on the Series 3 from April 1979.
- Not claimed
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Earth polarity, and the same unresolved Series 1/2 solid-or-ventilated front disc question as the XJ6.
