STELLENBOSCH, South Africa – The '07 Jaguar XK coupe and convertible are all-new – right down to the way they were developed.

Much convention was thrown to the wind for the second generation that abandons the steel body of the outgoing XK8, codenamed X100, which has been in existence since 1996.

The new X150 platform switches to an all-aluminum lightweight construction, and the products officially are renamed XK.

Additionally, the order of development was reversed, with the convertible body style engineered first.

Jaguar Advanced Lightweight Coupe concept was the basis for the new XK.

And Jaguar Cars developed the manufacturing processes simultaneously with the vehicle, in anticipation of moving assembly to a new plant.

"On this car, more than ever before, Jaguar engineers used virtual processes, building the new models in the virtual world a half-dozen times before building the first prototype," says Russ Varney, chief program engineer.

The auto maker was able to identify issues or missing parts in the virtual world, address them, and continue with the virtual build to prove out the fix.

Additionally, the car was modeled at the component level, as opposed to subassemblies or systems as was the case in the past, where modeling was used to ensure the modules interacted properly.

Zeroing in at the component level better ensures reliability. "The result was no surprises in the real build," Varney says.

About seven prototypes were built in developing the XK, compared with 100 or more prototypes required for testing in the past, he says.

And when the vehicle underwent crash tests, no changes were necessary. "Normally there would be an intrusion issue or something that needed to be addressed," Varney says. "Not this time."

Mark White, chief technical specialist-body structures, says there was, in fact, "zero intrusion."

The virtual validation allowed engineers to focus on finesse and sensory feedback (touch and feel), Varney says.

"Great cars are about (addressing) the last 1% (of detail and finesse)," he says. "Fantastic cars are the last 0.1%. We are approaching 0.1%."

The auto maker actually completed prototypes for the production model of the new XK 18 months before the Advanced Lightweight Coupe concept was prepared for the 2005 North American International Auto Show, Varney says.

The show car was a bow to pressure to exhibit something new from Jaguar, even though work was well under way on the production model.

The final production model differs little from the show car, with some changes to the fascia and a few other detail tweaks.

Jaguar also decided against the normal industry practice of designing a coupe first and essentially chopping the top for a convertible.

"We deliberately did the reverse," Varney says, "and designed the convertible first and improved on it for the coupe. As long as the convertible works, there is no downside to an even better coupe."

Both bodies were engineered at the same time and have 95% common parts.

The result is the new convertible is as stiff as the outgoing coupe, and 50% stiffer than the convertible it replaces.

Varney says his objective was to be able to put a person blindfolded in a car and have them unable to determine which body style they were in.

There is some carryover from the outgoing XK8, notably the 300-hp 4.2L V-8.

The suspension is a hybrid of the ones found in the S-Type and the XJ.

The aluminum body, electrical architecture and interior are all new.

Total number of parts in the body was reduced by 100, from 350 for the first generation, White says, with additional castings, extrusions and integrated stamped parts, and fewer than 3,000 joints, from about 5,000 on the old model.

Stampings on the XK, which represents next-generation Jaguar lightweight-vehicle technology, account for 76% of the parts, down from 89% on the XJ, which is first-generation technology. Additionally, the amount of castings and extrusions on the XK is double that of the older XJ, White says.

The engineering of the car was carried out simultaneously with the design of its new production facilities, in anticipation of the move from the Brown's Lane assembly plant in Coventry, U.K., to the more modern Castle Bromwich in Birmingham, about 20 miles (32 km) away.

To ensure a smooth XK launch, Varney says preparatory work at Castle Bromwich was under way before the decision to close Brown's Lane as part of Jaguar's restructuring efforts, which includes addressing manufacturing structural costs.

Essentially, Jaguar has consolidated production of its two aluminum-bodied vehicles in the same facility, creating a center of excellence.

The aluminum XJ and steel-bodied (for now) S-Type share a body shop, travel to paint, and then to a shared final trim line.

To add the XK, Jaguar gutted the conventional body shop of the outgoing XK8. The space required to build aluminum bodies is about one-third of that needed for steel bodies.

Finished aluminum XK bodies travel to the paint shop that is shared by all models, and return to the body shop where the unused two-thirds of the space now houses the trim and final assembly line.

Body and trim can co-exist side by side because there are no sparks to worry about with aluminum bodies, Varney says.

And having all the assembly in one building makes it easy to correct any problems detected. Because the XK coupe and convertible have 95% shared parts, it is easy to shift the production mix between the two body styles to meet demand.

Castle Bromwich is operating on a single shift but a second could be added if demand proves higher than anticipated.

The full benefit of transferring assembly from Brown's Lane will be realized this year and next, says Bibiana Boerio, managing director-Jaguar Cars Ltd. She says the real efficiency comes from the shared paint facilities.

The XK began production in December, and the vehicles are arriving in showrooms in the U.K. this month. They are slated to go on sale in North America mid-April.

apriddle@wardsauto.com