To mark the 30th anniversary of XJ40’s launch, we speak exclusively to former Jaguar Engineering Director, Jim Randle.
If the XJ40-series’ legacy represents a series of lasts, then chief amongst them is that it remains arguably the final mainstream British series production car to embody the single-minded vision of one man. Because if a car could embody the personality and mentality of its creator, then XJ40 is Jim Randle, whose stamp is all over its conceptual and engineering design. Recently Driven to Write spoke exclusively with the father of the ’40 to re-evaluate the final purebred Jaguar saloon.
A lot of early XJ40 work took place under Bob Knight during the 1970’s and I wondered how much of that carried forward to the car Randle developed from 1979 onwards. “I’d already been working on the car, developing suspensions [and] crush structures with Bob Knight. For that period, Bob was diverted anyway due to BL issues, so, I had it to myself.”
Randle then goes on to explain how the early stages of the car’s development became dominated by regulatory imperatives. “The key thing surrounding legislative requirements – one of which is crash performance – the structure had to be right in that respect. I did a lot of work in that area. We didn’t get it very far wrong on XJ40. We got it much better on later projects, when I understood it better.”
The subject of crush-structure is apposite however, as there are a number of myths surrounding XJ40 I’m keen to address. One of them I put to Randle is that the crush tubes were said to be purposely designed to entail the exclusive use of Jaguar’s in-line AJ6 engine, is this true? “It wasn’t crush tubes. Our friends at British Leyland wanted us to drop the AJ6 engine and put the Buick [Rover V8] engine in. So I developed a story which said: ‘look, we’ve done a lot of crush work’ – it was the structure going back into the bulkhead, which I’d got a very nice, square-ish box – I said: ‘We’re going to have to do it all again, because if that key stress carrier is changed, that’s going to be a big job; we’ve got to rethink the structure.’ Which is bullshit of course, but they swallowed it.”
The AJ6 engine was of course a key component of XJ40, designed to be lighter and more efficient for a new more austere landscape, one where big-engined luxury saloons seemed doomed. Today Randle is a little ambivalent about its merits. “Harry Mundy did a very good job on AJ6 and it was pretty bullet proof, [but] I think in principle, in terms of refinement, we made a mistake in having an inline aluminium six. A V6 would have been the more sensible project.”
He goes on to explain. “Six inline engines, aluminium block engines, are a bit of a problem, because the crank produces secondary forces which are resisted by the stiffness of the block. Aluminium blocks are not as stiff as a cast iron block, they don’t have the damping a cast-iron block has. A cast-iron crank is better, because it has its own internal damping, therefore the secondaries are not so bad. But we did have problems with the AJ6 in that respect. The problem is that the secondary forces being developed at the tail shaft go straight into the floor, which is a big sounding board. It’s quite an issue with that model, but we solved it with our mounting system.”
The AJ6 engine was initially conceived on the basis that it could be derived from existing V12 tooling – a process which took the powertrain team down some fruitless alleyways throughout the 1970’s. One in particular being the stillborn 60° V8. I’m interested in Randle’s view of its deficiencies.
“What happens with V8’s is that you get a 90° shift in the position of the crank; it’s got 90° intervals, and the block is set at 90°. That means you can get most of the problems out of it. Flat plane cranks and V8s don’t go well together, [they] run like four closely coupled Harley Davidsons. The 60° V8 was effectively a 2/3rds length V12. The only problem we had with the V8 in that form was the firing order down each bank was uneven because it had a flat plane crank. With a flat-plane crank, it just sounds like a big four [and] it did sound like a four. It also had secondary difficulties, and to overcome that, we were running a couple of twice-engine speed counterbalance masses alongside the thing. It wasn’t a nice engine, so we dropped it. Flat-plane, 60° V8s; there aren’t many of them and there’s a good reason for it!
Later XJ40 models came with a longer stroke four litre version of the AJ6. Was this a superior power unit? “It had better performance. [The] 3.6 litre had a cast crank, [the] 4.0 litre a forged crank. I think the 3.6 is more refined than the 4.0 – a lot of that is probably to do with the cast crank.”
Following his departure from Jaguar, a V12 installation was completed, following lengthy delays involving (again) the front structure of the car. Randle’s position on this skewers another sacred cow. “I really don’t know why they did that, [it] seemed illogical to me. If you wanted that power out of an AJ6 engine, you’d only have to turbocharge it, and you’d go way past what the V12 would produce.”
Something of course he could prove given that twin-turbo AJ6 engines were routinely producing well over 300 bhp in prototype form. But at the other end of the performance scale, Randle doesn’t believe the small capacity engine had much to commend it either. “Early XJ40s had that in – a 2.9 litre inclined engine. It was okay in terms of refinement, but it hadn’t got the power and performance.”
This engine of course featured a similar Michael May ‘Fireball Head’ to that developed for the V12 and its claims for ‘High Efficiency’ also receive a debunking. “It didn’t deliver its promise. It was going to be 13-14:1 compression ratio, and therefore it should have delivered more power and better economy. It didn’t really deliver that, and we finished off by nearer to 10:1 than the 13-14:1 that it promised. Expansion ratio is everything, so no, it really didn’t deliver too much.” With some mirth, he adds: “You know, the bullshit of putting H.E. on the back, I think, was probably as valuable as anything!”
Driven to Write thanks Jim Randle and Christopher Butt of auto-didakt for their kind assistance with this series.
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