Editing Jaguar AJ6 engine (section)

===4.0 (1989–1994)===

The 24-valve DOHC {{convert|3980|cc|L|1|order=flip|abbr=on}} version replaced the {{convert|3590|cc|L|1|order=flip|abbr=on}} AJ6 in 1989. It featured a longer {{convert|102|mm|in|2|abbr=on}} stroke, and generated {{convert|183|kW|PS hp|0|abbr=on}} power at 4,750&nbsp;rpm and {{convert|392|Nm|lbft|0|abbr=on}} of torque at 3,650&nbsp;rpm. The {{convert|3980|cc|L|1|order=flip|abbr=on}} engines as used in the 1990–1994 XJ40 cars continued with the crank sensor and empty distributor type of ignition system  and the hot-wire Mass Air Flow sensor type of fuel injection control system as the 1988–1989 {{convert|3590|cc|L|1|order=flip|abbr=on}} XJ40 cars.

[[Tom Walkinshaw Racing|TWR]] modified XJ40s resulting in the XJR. Jaguarsport was also formed as a partnership between TWR and Jaguar. The first XJR, the XJR {{convert|3590|cc|L|1|order=flip|abbr=on}}, had extensive appearance changes coupled with stiffer suspension, [[anti-roll bar]]/links, power steering valve that reduced efficiency by 40% and an LSD but no performance enhancements. Interior-wise it included special stitching, "sport" or "XJR" embossed front headrests, and Jaguarsport speedometer labels and tread-plates.

1990 XJRs had the upgraded 3L engine with the old style body-kits, and appearance changers.

XJR 1.0Ls from 1990 on had all of the XJR 3.6 handling upgrades and benefits from engine enhancements such as high lift cams, improved double plenum inlet manifold, and a compression ratio of 9.75:1. They were sent to TWR in Coventry to be modified directly after being produced.

The exterior changed again for the last generation of the XJ40 XJR (from H-registration year onwards). Bodykit was re-sculptured and the boot spoiler was deleted. Side mouldings were added, with the smaller "XJR" badge embedded in them. Engine had a plaque saying "Jaguarsport XJR 4L" on the rocker cover. XJR badge size was decreased on the boot (had previously ranged from XJR-3.6, XJR-4L, 4-litre and "XJR". The later one ("XJR") is most common and the only badge that could be chosen on the boot infill panel models. A "sport" one on the front within its own unique XJR grill. In this unique grill a "sport" badge was installed. Interior even had XJR specific wood (SPB part number).

Total XJ40 cars built was 208,733 and supposedly 500 JaguarSport cars built, 200 of the round headlight versions and then about 300 with the square headlights like the Sovereigns and Daimler's. 1990+ XJR power output is around {{convert|250|bhp|kW PS|0|abbr=on}} / {{convert|278|lbft|Nm|0|abbr=on}}.

The prototype Jaguar XJ41/42 sports car used a twin-turbo version of the AJ6 4.0, developing 330bhp.<ref>{{Cite web |last=Adams |first=Keith |date=2021-03-28 |title=Concepts and Prototypes : Jaguar XJ41/XJ42 (1982-1990) |url=https://www.aronline.co.uk/concepts-and-prototypes/concepts-and-prototypes-jaguar-xj4142/ |access-date=2024-06-21 |website=AROnline |language=en-GB}}</ref>