The AJ6
WHEN MOST new cars are introduced onto the market they’re usually redesigned bodies on an existing chassis or they’ll use several components carried over from a previous model such as an engine or suspension layout. It’s very seldom that a company will develop an all-new car yet that’s exactly what Jaguar did with the XJ40 during the Seventies and Eighties.
The reasons why most companies don’t design totally new cars is mainly due to the cost to retool everything. But it’s also quite risky due to teething problems often caused by new and therefore untested parts.
When I spoke to Jaguar’s then managing director, Bob Knight, plus engineering director Jim Randle about the XJ40 when the car was still in development it was clear they wanted to update all the technical aspects of the model and the only way of doing that was to change everything. In terms of engineering, it was an enormous project and I don’t think it had ever happened before in Jaguar’s history. Certainly my generation of designers and engineers had never done an all-new car.
I mentioned in my column in the October 2022 issue about working with Bob Knight who felt he needed to design cars because that’s what Sir William Lyons did, as if it was part of the job description of a chairman. But, as I also mentioned, not having the talent for this meant he usually relied on mathematics instead.
It was during one of our many all-night design sessions when I asked Bob why the new AJ6 engine was a straight six. He replied that Jaguar’s cars had become famous for their refinement which was in part due to the relative smoothness of the old XK engine. For larger engines to have this level of refinement they needed to have even firing plus primary and secondary balance. The V12 already had this because it was basically two straight sixes joined together but a flat six and a twin-throw crank V8 would have it too.
Bob said a flat six would offer plenty of torque but wouldn’t fit inside the XJ40’s new longitudinal crash tubes which were one of the big changes over the old Series 3 and needed for safety requirements. He went on to say a twin-throw crank V8 wasn’t an option either becau
