Jaguar XFR and XKR

 Officially, Jaguar’s new XFR is codenamed X250. Unofficially it has another name, coined early on by the development team as a wry statement of intent for what they wanted to achieve with their new sports saloon. They called it Weapon Of Choice.

There have of course been some fine R-badged Jaguar four-doors in the past, but in thuggish weaponary terms they’ve always been more towards the cricket bat end of things: still able to do a lot of damage but not the sharpest instrument in the world. The XFR is designed to change that. Along with the revised XKR, it forms a double-pronged attack on the perception of Jaguars as softies by being the sportiest, most sharp-edged saloon Jaguar has ever made.

Both cars use a brand new V8, developed from scratch in Coventry and sharing only cylinder head bolts and exhaust tappets with the old AJ-V8. Everything else is fresh, including an increase in capacity from 4.2 to 5 litres, the introduction of direct injection, and a cross-bolted bearing cap that gives extra rigidity and is innovative enough for Jaguar to have patented it. This being a thoroughly modern unit it boasts greater efficiency – partly achieved through a zealous quest to remove unwanted friction through engine and drivetrain – and suffice to say that the supercharged version which powers these R cars has the headline numbers – 503bhp, 461lb ft – to hold its own in a scrap with its German rivals.

However, the new unit isn’t just about an M5-matching power output. With dismissive modesty Malcolm Sandford, Jag’s chief engineer for engines, says ‘anyone can do that’ and adds that driveability was as important as outright grunt. That’s why this engine, unlike the V10 from Munich, delivers meaty slabs of torque low down, hitting its torque summit at 2500rpm and then sustaining that peak until 5500rpm. Despite a new push towards sportiness, the powertrain engineers believe low-down grunt is not only an important characteristic for any Jaguar but also more useful for the way people actually drive. Over the past few years they’ve asked a select band of loyal customers to carry data-loggers in their cars so the engineers could be doubly sure that instant pick-up at lower engine speed was more useful than outright revviness for the average Jag driver in the real world. 

The XFR’s claimed 0-60 of 4.7sec is impressive enough but it’s the in-gear stuff that really vindicates Jaguar’s belief that for instant oomph at any revs, they were right to stick with a supercharged engine. The 50-70mph time of 1.9sec is especially impressive. When we figured the 572bhp Audi RS6, the best it could manage between those speeds was 2.8sec.

The Jag’s got grunt then. The only sad thing is that there could be even more. The big V8 is reportedly capable of it but the gearbox – the same excellent ZF six-speed unit with paddle-shifter control as in regular XFs – would be getting close to its torque capacity and as a result the engine management is programmed to plateau the output. On the plus side, all that twist action means the torque converter can now lock-up from as little as 1000rpm in second gear to banish the ‘rubber band’ feeling that can make automatics feel dopey.

There are also developments at the back end of the drivetrain where a new, more rigid subframe supports a brand new diff featuring what Jaguar calls Active Differential Control, a system that uses a clutch pack controlled by a small, fast-acting electric motor to control the proportion of torque sent to each wheel. In normal, undemanding driving the system allows the car to run with a regular, open diff to the benefit of noise, efficiency and – since mechanical limited slip diffs can promote understeer in some circumstances – handling. But when things get more tasty the diff control can shunt torque across the axle, promoting better stability, better response and ultimately acting like a slippy diff so that if you’ve got the stability control off you can indulge in what Jaguar politely calls ‘controllable power-on oversteer’. Given the passion and enthusiasm of the team behind it what they really mean is, ‘We’ve built a bloody great drift car’.

The active differential works in league with other major chassis changes including  higher spring and anti-roll bar rates, and the faster steering rack first seen on the limited run XKR-S. But the most notable change is the introduction of a new active damping system which Jag calls Adaptive Dynamics. This replaces the old CATS system seen on R saloons for many years and has the chief benefit of being progressively variable rather than adjusting itself in steps, all the better to adapt to roll, pitch, yaw and the road surface it’s travelling over in as subtle and effective way as possible. There are no foolishly compromised ‘comfort’ and ‘sport’ modes either. The only driver control over the system happens if you push the XFR’s ‘Dynamic’ button, at which point the dampers start to work within a narrower range towards the top of the spectrum to give tighter body control, whilst at the same time the throttle response sharpens, the gearchanges get more aggressive, the stability control becomes a tad more relaxed and the whole car becomes even feistier for the amusement of really keen drivers.

It’s no surprise that Jaguar owns a BMW M5 and that this was seen as the XFR’s chief rival. But Mick Mohan, Jaguar’s director of new car programmes, says the decision to make the new R car more hardcore actually came from the success of the XF SV8, a car designed to be a refined cruiser but which actually surprised with its agility and the sprightliness of its old-generation supercharged V8. ‘It was touch and go for a while whether we even introduced the SV8 at all,’ Mohan admits. ‘But when people drove it they were full of praise and that gave us the confidence to make [the XFR] more focussed and more edgy.’

Since the SV8 also looks all but identical to the basic XF diesel, it’s discreet to the point of invisibility. Clearly for the R that wouldn’t do and design director Ian Callum already had a plan to make changes, largely to the lower reaches of the car since, as he says, ‘that’s where the physics happens’. But the resultant alterations weren’t just for style. The designers asked the engineers what they needed for aerodynamics and for engine cooling demands and then worked to those specs so that form followed function. The result is a new front bumper with gaping, chrome ringed air intakes either side, new sills that flare out rather than tucking under and a new rear spoiler, all tweaked and tuned in the wind tunnel. There is one bit of more styling-led design – Callum wished he’d given the original XF sharper corners on its nose and with the XFR he’s achieved that, adding two taut lines running vertically outboard of the air intakes. But even those turn out to have an aerodynamic benefit, giving more defined airflow down the body sides to the benefit of stability. Finally, there are quad exhaust pipes, giving a subtle hint of the mighty lump up front, and handsome 20-inch wheels to a design taken straight off the C-XF concept car.

Inside, the most significant change is a set of brand new front seats which XF chief engineer Kevin Stride describes as ‘some of the best we’ve ever done’. With their large – and adjustable – side bolsters they certainly look appropriately sporty, especially in a bold new colour option called ‘Red Zone’. No-one expects many customers to order them, but for Ian Callum it’s an important statement of intent and a way of showing that Jaguars don’t have to be all about old-fashioned burr walnut and cream bloody leather. For the same reason, the R will be available in two unique and rather vibrant new paints, a red and a blue. Apparently when the first line-built XFRs came down the track at Castle Bromwich there was a palpable air of excitement as a red shell appeared and the assembly workers discovered that, after all the usual black, grey and silver XFs, for once they’d get to work in Technicolour.

You’ll have noticed that the XK has also been given a cosmetic tickle to go with its new engine. There’s a fresh front bumper with vertical slots at its extremes – designed to make the car look wider and more substantial from head on – and smarter, LED tail-lights to match the new LED repeaters in the smoother door mirrors, but otherwise the pretty shape is wisely left well alone.  The interior has likewise been tweaked only where it needs it, chiefly with the addition of the XF’s better-than-a-gimmick rotary gear selector. The real story is the arrival of the 503bhp V8 in the XKR (the regular XK gets the new nat-asp 5-litre and all the cosmetic tweaks bar a shiny lower grille mesh) plus the tricksy diff and adaptive dampers.

There’s another neat twist too. For some time Jaguar V8s with normal breathing have enjoyed cunning pipework behind the dash to feed tantilising engine rumble into the cabin, but it’s a system that’s been denied supercharged models because all the ducting would do is pipe in the whine from the blower. However, the new ’charger, being more efficient and more refined, barely whines at all which means that in league with a ‘filter’ system on the sonic tubing – tuned, Jaguar says, to tenor C – both XKR and XFR drivers can enjoy a subtle but noticeable reminder of how many cylinders they have. The XKR takes this one stage further with Aston or Ferrari-style active exhaust valving to give a fruitier pipe note under pre-programmed conditions like hard acceleration. Or you can press the ‘Dynamic’ button and the valve opens permanently. Which is nice.

Pesky launch schedules being what they are, we haven’t driven either of these cars yet, but we have been out with Mike Cross, Jaguar’s chief engineer for ‘vehicle integrity’ or the bloke who makes sure Jags drive like Jags, for a brisk run around the twisty, tight and often appallingly surfaced Warwickshire lanes where much of these cars’ dynamics were gently buffed and honed. As a result we can report that the XKR feels slightly more taut than before – Cross says it’s designed to have ‘60 to 70 per cent of the character’ of the more hardcore XKR-S – and is clearly mighty fast, but in all other respects appears to keep all the surprising agility yet beguiling comfort that always made that car a charmer.

The really intriguing bit of kit is the XFR, which again is clearly beltingly quick and keen to play yet comfortable enough to make you consider a pointless overnight drive to Aberdeen. From the passenger seat the best way to describe its feeling of extra edge over a regular XF is to imagine the difference between squeezing your bicep when your arm’s relaxed and when it’s tensed.

On paper then, and from the passenger seat, these promise to be the sportiest, most driver pleasing Jaguars for years. And they might not be the last. Pressed on whether he’d fancy developing a more hardcore car to follow the old XKR-S, Mike Cross talks about market conditions and customer demand before adding an enigmatic ‘If people wanted it, we know what we’d do’.

The new engine

Ralph Hosier was one of the development engineers on the new V8

Jaguar’s new engine, codenamed ‘AJ133’,  represents the boldest step in Jaguar engine design since the E-type’s V12. Like all of Jaguar’s great engines (XK, V12, AJ6, AJ26 V8) it has taken the best technologies available at the time and blended them into that unique Jaguar cocktail.

The first stages of development, way back in 2001, involved proving out each new aspect, so a highly modified current production engine was the first to run the new direct injection system. The first real prototype engines (batch 1) were created in 2004 and immediately began relentless testing  on ‘dynamometers’, where each engine is mounted on a dedicated ‘pallet’ that supports all the test equipment and all the myriad ancillaries needed to make an engine run. Some did specific tests, such as trying to deliberately foul the spark plugs, or pushing the performance limits; others were run on durability cycles designed to stress components to the max. Many a time I walked past a test cell where the exhaust manifolds were glowing bright orange as an engine was run at full tilt.

It soon became clear that both the naturally aspirated and blown versions would meet their performance targets with ease. I drove one of the first cars with a prototype engine in 2007. The engine calibration was a ‘first cut’, a sort of best guess starting point with no refinement or drivability tuning. It was raw and more than just a little bit wild. Driving in the pouring rain with no traction control led to a few moments of unintended excitement; overtaking a moped, the gear changed and the engine pulled a little too strongly; the car roared through its pre-prototype exhaust and there was a degree of sideways progress, much to the surprise of the moped pilot.

With the first test cars built, the gearbox department were flat-out refining a lighter yet stronger version of the ZF six-speed paddleshift auto. Everyone acknowledges that this is a world-leading gearbox. The genius is in the way it works in total harmony with the engine; when changing gear the ’box asks the engine to adjust power to balance not only input speeds but also the kinetic energy in the system. Ten or more electronic messages are passed between the engine and ’box during each shift and it all happens in a fraction of a second.

Prototypes are driven in every type of environment so the design can be finalised before test cars are sent for official emissions certification all over the world. So cars are out and about with disguise kits on years before launch, trying to avoid the hoards of press photographers camped out in the hedges near the factory. Whenever ‘spy shots’ of a new car are printed it’s standard practice to work out who was driving and then mock them mercilessly, although it should be mentioned that in some cases they can face disciplinary action.

How advanced is this engine? One example. The use of Gasoline Direct Injection (GDI) controls combustion in such a way as to effectively shape the way the cylinder pressure rises and falls as each cylinder fires. When you hit the start button the engine will synchronise, analyse the current air and coolant temperature, check all the sensors are working, set the fuel pressure on the twin double-acting high pressure pumps, check and adjust throttle angle, set all four cam positions, charge up the ignition coils and the 160volt injector control circuit and be ready to fire the first cylinder within one revolution of the engine.

If you ever get to drive one of these wonderful cars, I’d just ask that you take a moment to look under the bonnet – a lot has gone into that space.

Specifications