McLaren dreams up spanking-new engines about as often as the census gets taken, and this one’s a humdinger, boasting a funky angle, a powertrain chimney, a first-of-its-kind axial-flux motor, and even a tri-clutch transmission. Let’s give you the pub ammo to become an instant expert.
Why a 120-Degree V-6?
For its first “Super Series” hybrid, McLaren was extremely keen to minimize weight and maximize the Artura’s agility. Sawing off two cylinders reduces both the engine’s weight and length, and splaying the cylinder banks to a 120-degree angle also lowers its mass in the car for improved handling. Six-cylinder engines want to fire every 60 degrees of crank rotation, so the six connecting rods can share three common crank throws as long as the bank angle is 60, 120, or 180 degrees. Packaging a smoother running flat-six was impractical, so 120 degrees was chosen and a counter-rotating balance shaft is fitted to quell the V-6’s inherent imbalance. Weighing in at 353 pounds, it undercuts the V-8 by 110 pounds, and its 5.9-inch-shorter overall length (partially achieved by placing the chain drives for the camshafts and the oil scavenge/pressure pump and coolant pump on the back of the engine) helped shorten the wheelbase by 1.2 inches relative to the rest of the McLaren lineup, further enhancing its nimbleness.
“Hot-vee” engines are all the rage now, but McLaren goes a step further, making its two mono-scroll turbos mirror images of each other, rotating in opposite directions. Economizing and using the same turbo for the left and right banks generally results in asymmetric exhaust plumbing, which introduces inefficiencies and often compromises the sound. This setup keeps exhaust pressure losses to a minimum for peak turbo efficiency, while ball bearings in the turbos reduce friction for faster spool-up. Note that the outboard-mounted intake plumbing is so much more compact than outboard-mounted turbos that, despite the wider bank angle, the M630 engine measures 8.7 inches narrower than the M838T and M840T V-8s.
Several complex heat shields surround the engine and hot-vee to cool it and prevent heat from seeping into the passenger compartment. Nozzles feed air from the back of the high-temperature radiator through the vee and out through a “powertrain chimney.” This opening in the heat shield vents heat through the center of the rear deck mesh. The exhaust does not exit here as in a Porsche 918 Spyder. Rather, it flows through a particulate filter, catalysts, and mufflers to exit between the taillamps. This keeps it out of the way of the full-width rear diffuser.
Formula 1 3D-Printed Casting Cores
McLaren’s not quite ready to 3D-print an engine block, but the next best thing is 3D printing the intricate cores used to cast the block. These extremely precise cores permit the cooling passages between cylinders to be just 0.08 inch wide—that’s just four to 13 times the diameter of a grain of foundry sand.
Undersquare Design With 8,500-rpm Max Speed
An 84.0mm bore and 90.0mm stroke delivers 2,993cc displacement, while that short, stiff, three-throw crankshaft is tough enough to withstand brief excursions to 8,500 rpm. The redline is painted at 8,200 pm, and the power peaks at 7,500 revs, so your prime motivation for kissing that 8,500-rev mark may be to revel in the sound this short exhaust and carefully tuned induction system generate.
Mighty-Mite Axial Flux Motor
Nearly every other EV motor in use today features a radial-flux design, where the magnetic field radiates out perpendicular to the axis of rotation. Such motors typically place their permanent magnets on the rotor with their N-S axis radiating outward. Axial-flux motors turn that all sideways so that N-S magnetic field is parallel to the rotation axis. Picture a ring of stator coil segments sandwiched between two iron rotor discs, each with permanent magnets arranged so that a north pole is always aligned with a south pole on the opposite disc. This places the magnets farther out from the axis where they can exert more leverage for better torque. The stator windings also fully utilize all their copper with no “coil overhang,” and the magnetic flux path is typically shorter. Finally, axial-flux motors generate less heat, and the heat they do create is easier to remove. For all these reasons, McLaren claims that at 34 pounds, the Artura’s 94-hp motor packs 33 percent more power per weight than the P1‘s 177-hp radial-flux motor.
Eight-Speed Tri-Clutch Transmission
Two clutches handle the eight ratio swaps like we’re used to, and the third one disconnects the engine from the transmission to allow the electric motor to power the car. When it’s doing so, the transmission typically shifts up through all the gears in case the engine needs to fire up and kick in. Despite adding a forward ratio and a compact axial-flux motor, nesting the twin clutches and deleting the reverse gear (the electric motor just turns backward for reverse) helped shrink McLaren’s new transmission’s overall length by 1.6 inches.