The Jaguar X308 XJR is a fabulous under rated machine and should go down in automotive history as a thoroughbred. The truth is that it probably won’t and will fall into the same chasm resided by It’s predessor the XJR (6 cylinder) where values plummet . There is no balanced appreciation in this fical world but so much the better for us enthusiasts. The truth is that this has got to be one of the most under rated saloons of recent times. I have much experience with these from the late 90s
The X308 combines a timelessly beautiful low slung body style with a very efficient and characterful V8. The suspension carried over development advances from the then recently launched X100/XK8 coupe. The structure is from the XJ40 of the 1980s. This is no bad thing: The XJ40 conceived in the late seventies/early eighties and was designed to meet the impending US 40 mph offset crash regulations which never materialised. At the time Jaguar had spent too much developing the hefty XJ40 structure to reoptimise for a lighter structure (the way the contemporary BMW E32 Seven series was). The fortunate upshot of all this as regards the X308 XJ is that it has a very robust structure. According to the UK Department for Transport’s road accident statistics which shows risk of injuries to car drivers involved in two-car accidents on a model-by-model basis whenever an injury is reported, the X300/X308 series Jaguars were among the safest cars on UK roads (measured in terms of chance of death in an accident over a four year assessment period) – three times safer than the safest Volvo models and matched only by the contemporary Mercedes-Benz S-Class. This publication presented estimates of the risk of driver injury in popular models of car, if they are involved in a two car injury accident. It does not address issues of primary safety and gives no information on whether or not specific makes of car have different risks of being involved in an accident. The statistics were based on personal injury road accident data reported to the Department for Transport by police forces within the United Kingdom.
The proportions of the car are wonderfully balanced. In true Jaguar tradition this style of saloon is form over function, as low as most coupes (if not lower than todays over bloated current crop), wide, with an imposing front but without being vulgar and the trade mark tapering rear end. Understated and very fluid.
Outside there is subtle dechroming but just enough bright work to compliment and highlight the svelte lines. It was this style of Jaguar that lead to a Milanese panel of experts voting it LAutomobile piu Bella del Mondo or The Most Beautiful Car In The World, surely a testament to its stylist, the late Geoff Lawson. It was the first year that this accolade was awarded to a non- Italian automobile. Compared to the contemporary German and Japanese opposition the X300 of this era are certainly form-over-function except that with the arrival of the X308 that a very efficient, light weight power plant mated to the superbly refined and robust Mercedes Automatic gearbox (WA580)and especially with the fitment of the R1 option Brembo 355 mm brake discs with 4 pot calipers- the function part of that equation was balanced up nicely.
The X308 XJ series was the last of the Jaguar saloons to be built at Jaguars famous Browns lane plant (the subsequent X350 model was made at Castle Bromitch).
A modern car of immense character the X308 is the ultimate blend of old and new. Not unlike the legendary Porsche 993 series 911s in this way.
The engine is up to the minute of lightweight (200 kgs dry weight) construction with low overall engine friction with 32 valves of direct acting bucket design and good flowing ports facilitating its high revving capability .The big valves (representing 42% of the bore size) formed part of lightest in class direct acting valve train.
The crankshaft is supported by a bedplate which anchors the mainbearings together and adds rigidity to the bottom end. The cast aluminium bedplate used iron inserts to control bearing sizes tightly-as required for tight oil pressure cpntrol demanded by the variable cam phaser units. The crankcase is split and sealed together with RTV. Like BMWs of this era the earlier versions of this engine featured a parent metal bore that was nicasil coated. This was replaced with iron liners in 2000 after a spate of prematurely worn engines that exhibited excessive bore wear showed up in certain regions where there was high sulphur content in the fuel.
Fuel injection is by Nippon Denso, drive by wire electronic throttle with variable cam phasing and an 5th Generation M112 Eaton supercharger on the “R” variants. The idle speed control not only uses the throttle to moderate the idle speed but a patented method of using the ignition timing as a short term strategy- where by the instantaneous acceleration of the crankshaft is monitored continuously and the ignition timing is moderated accordingly. The AJ27 cars (post 2000 model year) had air shrouded injectors for better fuel atomization. When first launched the AJ26 V8 must have sent shivers down the spines of the rival counterparts at Stuttgart and Munich. The valve train featured direct acting mechanical buckets (something of a Jaguar tradition)– with the lightest valve system mass in its class at 100 grams (including valve , spring collette etc) which in turn allowed aggressive valve accelerations. It was decided to not go with hydraulic valve lash compensation – trials showed that even after well after 110,000 miles the valve lash was well within specifications-such was the tribological pairing of cam lobe to tappet materials and the quality of modern lubricants. If you compared this to the contemporary BMW M62 of the time- which had hydraulic tappets – a fairly sizeable heavy tappet mass reciprocating. This is clearly shown when you analyse the valve lift profiles of the BMW V8 and Jag V8 with the Jag pushing valve accelerations of 0.027 mm/deg^2 and the BMW at 0.020 mm.deg^2. In addition that Bavarian V8 engine had yet to attain variable cam phasing and made a lot less specific output in terms of both power and BMEP. As for the twin plug 3 valve per cylinder Mercedes engines of the same era- well they were certainly very lightweight but had a slow burn rate, were quite knock limited at full load at quite moderate BMEPs and had poor specific output, BMEP and no variable cam phasing. Although it must be said of the Merc that it is capable of running quite diluted charges without misfire thanks to its twin plug configuration and the cylinder deactivation system was both innovative and interesting.
The XJRs overall engine air flow level is around 1100 kg/hr- the intake manifold depression or intake losses are around 115 mbar with an exhaust back pressure of about 750 m bars at peak power. These losses are ok for a supercharged car but there is a lot of room for improvement
Suspended by double wishbones all round, the rear suspension system a direct evolution of a concept that can trace its lineage back to the 1960s but optimized and brought up to date.
The XJR steering is only 2.8 turns lock to lock. It is direct but very lightly weighted- a bit too light for our tastes. It could also do with a bit more castor or steering self centering. The ride is pleasantly soft for a boulevard cruiser although there is a bit too much roll for a sporting car in the ‘R’ variants. The US spec cars indeed have different springs and dampers. In the US spec cars when sliding the rear end it is possible to get the car caught in series of tail slides initiated by the roll induced lurch of this great ship. The secondary ride is a bit harsh due to the low profile tyres. Overall the suspension is well judged for the market it was intended and indeed the low speed ride is glorious compared to the jittery air suspended X350 which followed. Around the skid pan contemporary road tests attained 0.87 to 0.88g cornering force before terminal understeer ensued. This is a great figure for such a colossal saloon and similar to a Mid nineties Porsche 928 GTS.
The car is exquisitely refined- even compared to the model that followed. It’s no secret that the noise transfer functions changed a great deal with the aluminium construction and a HUGE priority was put on the X350 to get that car to be less boomy nevermind matching the serenity of its predecessor. The performance is scorchingly quick with the 0-60 mph dash taking about 5.3 seconds and a standing quarter mile passed at high 13s. It’s relatively cheap to make modifications to the XJR powertrain to get a lot more power. The supercharger is only driven at 2:1 drive ratio and the peak engine revs are 6150 rpm (the naturally aspirated engine revs to 6800 rpm). Eaton says the M112 has a peak rotational speed of 14000 rpm- which means there is some room to increase pulley ratios for more power if you’re willing to change the supercharger drive belt more often.
The interior is still something of a cosy gentlemans club with lashings of walnut veneer and leather. However the seats offer good lateral support and are no armchairs. The deep pod instruments take some getting used to but after all this time have become something of a signature of the X308 XJ series along with the rest of the ‘spitfire profiled’ wood veneer. It’s often cited that the X308 is cramped and these musings are vastly exaggerated. I’ve heard folks liken the interior room to that of a sub compact. I guess it depends on your frame of reference. I’d rather have the interior room of the X300 series –which is more than adequate for a small family-and the gorgeous silhouette that goes with it than more room and a non descript and non distinctive testimony to ubiquitous conformity.
Dissapointments and what would we have done better? Well I think it’s a poor showing that the secondary chain tensioners on these cars took Jaguar 3 design iterations to get right. You should be ok if you purchase a 2001 model year or later. I wouldn’t let it dissuade me from buying a good condition one- just make sure you upgrade to the latest secondary chain tensioner. The aforementioned pulley ratio change would be a worthwhile modification, while focusing on the airbox- perhaps using one from a later 4.2 litre XKR with additional orafice- will help to de-restrict the supercharger. The exhaust systems 750 m bar back pressure could be reduced with larger sectioned tubing and larger silencers (if noise levels want to be retained at their current level). There is no decent system on the after market today that attains a reasonable back pressure of around 500 mbars or less unfortunately. All we see are an array of overpriced overhyped branded systems from Jaguar “boutiques” trying to exploit discerning customers for top dollar.
In addition I think it was poor judgement on Jaguars part to drop the limited slip differential of the previous series (or powerlock) and the safety factors and strength of the fitted 14 HU differentials of the X308 are low and no where near as strong as the legendary 15 HU and 4HU units fitted to previous generation cars and enjoyed by many hot rodders. As a result on the R supercharged cars, you may get lucky and have no problem or you may have big problems with the crownwheel /pinion teeth sheering off.
Bring this chariot up to date: we would love a 550-600 Bhp TVS1900/2300 Eaton supercharged beast, with 15 HU differential, powerlock, a modest capacity increase to 4.6- 4.8 litres and the Mercedes gearbox tuned to be a tad more responsive