An entirely new six-cylinder engine, in the XJ-S Coupe or a new Cabriolet, was Jaguar’s autumn announcement unveiled in time for the Motorfair. The in-line six has a capacity of 3.6 litres and develops 225 bhp DIN, aided by twin chain-driven overhead camshafts and four valves per cylinder. The power unit, in two forms, will be at the heart of the XJ40 saloon which is due for announcement early in 1985, when a “standard” destroked 2.9-litre version with the May head will also become available.
This is only the third new Jaguar engine to be produced in the post-war period, the first being the legendary XK six-cylinder engine which appeared in 1948, the second being the V12 which was installed in the E-type, and later in the XJ-S and Jaguar / Daimler saloons, from 1971.
The AJ series engine is mainly aluminium, this material used for the block, head and sump, with thinwall cast iron liners. It has the same bore centres as the XJ12 so that the same cylinder head can be used later on, and retain the 12-cylinder’s generous seven main bearings, so it remains a comparatively bulky and long power unit. It differs from the HE “12” in having a dry liner closed deck block, rather than a wet liner open deck, in the interests of weight and torsional stiffness (apparently it was considered at one time to have a Diesel version, but this plan was abandoned).
Jaguar’s design team had been mulling over a replacement for the XK since 1970, first malting a V8 version of the V12 which was considered not smooth enough. Then they considered putting a 24-valve head onto the iron block unit, but came to the conclusion that the block itself was not capable of further development. Then they cut the V12 in half to use one bank of six, but found that at 2.6 litres it did not develop enough power… and, wishing to keep the 90 mm bore so that the heads would be interchangeable, they increased the stroke but that made the engine too tall.
In the end it had to be a completely new design, one in which more than E30 million has been invested. It’s no less than 180 pounds lighter than the XK (say 25%), is 10% more powerful at the outset, and will probably use around 20% less fuel. Lucas electronic fuel injection is used, as on the 12-cylinder, with unusually long 17 in inlet tracts which give a good “ram effect” for mid-range torque. The engine develops 225 bhp at 5,300 rpm, and 240 lb ft of torque at 4,000 rpm; the compression ratio is 9.6:1, the 24-valve head featuring a pent roof, and domed pistons are fitted.
The AJ6 unit has a bore and stroke of 91 x 92 mm producing a capacity of 3,590 cc, such square dimensions being rather unfashionable nowadays though due for a much shorter stroke when the 2.9-litre version comes along, probably producing in the region of 160 bhp DIN with the 12.5:1 compression May head, and two valves per cylinder.
To begin with the AJ6 drives via a Getrag five-speed gearbox similar to that in the coupes contesting the European Touring Car Championship. It is a welcome development from Jaguar whose more sporting products have been available only in automatic form for several years now, though it has to be said that the XJ-S 3.61s still very much a Grand Touring car, rather than having great sports car appeal. The lack of an automatic version initially 15 explained by the fact that the AJ6 engine will eventually be mated to a new, four-speed automatic which will suit its characteristics better than the GM400 box now fitted in the 12-cylinder versions.
Apart from the fluted bulge in the bonnet to accommodate the slightly taller engine, the Coupe is little changed, having the same brakes, power steering and suspension design, though the front spring rates have been lowered to take the lighter overall weight into consideration.
The Cabriolet has a fixed roll-over bar and a detachable “Targa” top which fits the overhead section; aft of the bar, the driver can choose between a conventional folding hood or a double-skinned GRP panel which incorporates a heated, glass rear window, so the model maimed for maximum year-round versatility. The fabric tops are fitted by Aston Martin Tickford’s new factory at Bedworth, Coventry, on a line alongside one for the new Tickford Capri.
Available only in six-cylinder form, the Cabriolet version has been stiffened along the transmission tunnel and incorporates a rear cruciform member. Quite substantial changes had to be made including reworked header rails, cant rails and 13-posts. Then the rear “flying buttress” was cut away, the rear wings changed and a new panel fitted ahead of the boot, the luggage compartment itself being unchanged (as is the 20-gallon tank capacity). The Cabriolet is, however, purely a two-seater as the space behind the front seats is converted for luggage carrying only.
Sales of the XJ-S are expected to build up rapidly, from 4,500 units this year to around 6,000 in 1984 and eventually to 9,000. Keen pricing will help. The Coupe 3.6 is priced at £19,250 including tax, the Cabriolet at £20,756 which is within a few pounds of the XJS-HE, the latter model now having a trip computer, cruise control and a headlamp wash / wipe as standard equipment. Included in the price of the 3.6-litre models are air conditioning, stereo radio) cassette, remote control mirrors, central door locking and tinted glass; the Cabriolet has a different pattern of alloy road wheel, and leather upholstery included in its price.
On the Moor
Dartmoor is infamous, perhaps, for its prison and its sometimes inclement weather. Jaguar managed to avoid the first for the launch of the new models, but a mist prevented us from extending the cars to check the performance. Top speeds of 145 mph are claimed for the six-cylinder Coupe and 142 mph for the Cabriolet, with 60 mph corning up from rest in just 7.6 sec. Up to 30 mph the five-speed 3.6 is actually quicker than the V12, the times to 60 mph being identical on paper, but then the HE goes on to 100 mph in 17.5 sec while the six-cylinder models take a still impressive 20.1 sec to reach the same mark.
A weight saving of 95 kilogrammes (210 pounds) bringing the kerb weight down to 1,660 kg is clearly a help, and so is the excellent Getrag gearbox which has a positive action infinitely smoother than the unit formerly fitted in the &type. Fifth gear (even higher than the VI2’s auto top gear ratio) gives a long-legged 28.4 mph / 1,000 rpm, which translates to 2,464 rpm at 70 mph.
This is likely to be good for fuel economy, and Jaguar’s claim of around 25 mpg in mixed driving incredible. Using the gearbox quite a lot, and peaking at 120 mph on a clear stretch of road, our trip computer told us we were averaging 23.5 mpg which should be easy enough to improve on a steady run.
The new engine has the right Jaguar sound, a similar exhaust system keeping the subdued, purposeful growl. Higher up the speed range at around 5,000 rpm there is a new, more exhilarating sound of 24 valves at work. The car feels impressively quick, though it seems to be running out of urge at around the 100 mph mark and is, perhaps, a bit low on power-to-weight ratio compared with the 295 bhp 12-cylinder.
Any new Jaguar is exciting, and the additions of a completely new power unit — especially one as advanced as the A16, with years of development ahead of it — and a new Cabriolet body style bring fresh appeal to the Coventry company’s line-up. As we know, productivity is substantially higher than it was three years ago, the factories are working at maximum production levels and all the export markets are booming, so the newcomers could not have come at a better time. — M.L.C.