At its most basic, the 2008 MINI Cooper shares most of its structure with the car it replaces. From the A-pillar back, the structure has been upgraded but not redesigned. There are new reinforcements in the doors to meet the U.S. government’s latest side impact standards. A brace was added to the exhaust tunnel to increase structural rigidity. All of the exterior body panels are new because the taller front structure—it is designed to meet the European pedestrian impact legislation that requires space between the hood and “hard pieces” (engine, strut towers, etc.) underneath—raised the base point of the windshield. That, in turn, meant the beltline had to be raised to retain the MINI’s “bulldog” stance.
About that front structure: It not only raises the hood and lengthens the nose slightly, it houses a new family of engines jointly designed and developed by BMW and Peugeot. Like most of BMW’s recent motors, it uses an aluminum bedplate to anchor the main engine structure. However, unlike the normally aspirated inline sixes introduced on the latest 3 Series, this structure is surrounded by more aluminum, not magnesium. That’s much more technology than found in the previous motor—a joint venture with Chrysler pre Daimler that is built in Brazil under the “Tritec” name.
Erich Sonntag is the drivetrain project manager for the new MINI, a job he’s had since the 2001 feasibility study began. “Peugeot wanted a high-technology engine to replace its aging four cylinder engines, and felt it couldn’t accomplish this on its own,” says Sonntag. “BMW wanted as low cost a motor as feasible, and was interested in exposing itself to a group of suppliers with which it had little or no previous experience, but who worked closely with Peugeot in the past.” Also, it didn’t hurt that joining with the French automaker for this project would greatly increase the potential volume for the engine—it will replace about 70% of the Peugeot group’s current engine lineup in its various guises—thus lowering its unit cost.
Cost control was on Sonntag’s mind from the very beginning, especially as the motor was scheduled to make use of technologies like direct injection, Vanos (variable valve timing) and Valvetronic (variable valve lift), an on-demand water pump, flow-controlled oil pump, and–for the Cooper S—twin-scroll turbocharging. “We looked at what the team wanted in terms of output throughout the life of the engine,” says Sonntag, “then started our material investigations with the lowest-cost aluminum alloys and worked our way up until we found the least expensive one that would meet our needs.” Working down from an expensive material, he opines, would not have worked as engineers are reticent to abandon a solution that works to one that may not. “When my process engineers told me there was no way to cut costs any further, we’d go out and look at the engine together to see if we couldn’t take out even more material,” he says. The process was a near-textbook definition of the word “obsessive” in that it often meant rounding corners to remove small amounts of aluminum. Sonntag admits the time spent on cost reduction and analysis, “was greater than most companies would accept,” but the result is an engine that hit the cost and technology targets. Minus the Valvetronic and Vanos systems, he claims, the Hams Hall, England-built engine costs the same as the Brazilian-built Tritec it replaces.
The new engine has 84-mm bore centers (the Tritec has 85-mm centers), and the block is slightly smaller than the old engine though the complete motor’s box volume in slightly larger. This is due to the introduction of the cam timing technologies and the fact that Peugeot wanted to build the new motor on the same line as its four-cylinder diesel. In addition, the motor comes in two sizes—1.4- and 1.6-liters—though the smaller engine is designed for Portugal and Greece where Peugeot has large volumes and tax legislation favors it over the 1.6-liter version.
“We use the same intake design for both engines,” says Sonntag. He calls it a “straight-to-the-point” design that does without dual runners or their internal valving, and is made of plastic and supplied by Mecaplast (www.mecaplastgroup.com). The fuel rail also is plastic, though the injectors are not on the manifold because there was some concern that the intake—now on the backside of the engine—would be rotated up and over the engine in a frontal impact. On the normally aspirated Cooper engine (118 hp @ 6,000 rpm, 114 lb-ft @ 4,250 rpm) the injectors and throttle body are sourced from Siemens VDO (http://www.siemensvdo.com), while the 0.8-bar twin-scroll turbocharged direct-injection Cooper S engine (172 hp @ 5,500 rpm, 177 lb-ft @ 1,600 to 5,000 rpm) uses Bosch injectors (http://www.bosch.us). Both engines use a Bosch engine controller, though it allows a 15-second over boost on the Cooper S motor that raises torque to 192 lb-ft.
Other common components include head castings made using the lost-foam process, tubular steel exhaust headers (“They cost the same as the old cast-iron design,” says Sonntag.), a serpentine accessory belt drive that has a stamped steel arm attached to a torsion bar, a Delphi-supplied (www.delphi.com) Vanos valve timing system, and an electric motor that eliminates contact between the water pump pulley and belt when the engine is cold. (If the system fails, a spring returns it to its full-contact position.) You can understand why Sonntag says, “We’ve never done as many calculations as we did on this motor. There was no budget for trial-and-error.”
The excess was spent elsewhere, including redesigning the multi-link rear axle to remove 13.2 lb. of weight by shifting to lighter aluminum longitudinal arms specifically designed for the MINI instead of adapted from BMW’s 3 Series. It also included fitting a new interior made of stouter, more luxurious materials, narrowing the center console by fitting the audio head unit into the—much larger—central speedometer nacelle, introducing a new side airbag design that deploys from the B-pillar outward, replacing the electro-hydraulic steering of the previous model with an electric system that adjusts its boost to the speed of the vehicle, adding an optional “Sport” button for more aggressive steering and throttle settings, fitting both the Cooper and Cooper S with a standard Getrag 6-speed manual transmission or optional 6-speed automatic with steering wheel-mounted shift paddles, and replacing the key with a round signal transmitter and separate dash start/stop button. In addition, the combination of traction control, ABS, electronic brake force distribution (EBD), and corner brake control (CBC) are standard on both models, while dynamic stability control is available as an option. It is enough, it can be said, to make the 2008 MINIS new, but still very familiar.