September 19, 2020

90 percent no BMW engine

The new 3.0-liter 6-cylinder turbo from M GmbH has nothing to do with that from the civil BMW models. How the high-performance machine is designed and built.

A quick look at the technical data suggests that the engine for the X3 M and X4 M is derived from the X3 M40i engine and, thanks to two turbos, has more power than a twin-scroll charger – that’s it.

But far from it. The effort does the brand name “Bayerische Motorenwerke” credit and could make fans with gasoline in their blood wistful. Because the days of such ultra-complex combustion engine construction are likely to come to an end. But from Garching it can be heard that hybrid or electrical engineering will only be offered in M-models if they promise performance advantages – without ruining the lateral dynamics with excessive weight.

Hardly any common parts with the “normal” six-cylinder turbo

Until then, BMW’s sporty daughter will treat itself to lots of extra white sausages: Compared to the unit from the X3 M40i, the degree of relationship is limited to less than 10 percent of the parts. Only the crankcase cover at the rear, the variable valve control (Valvetronic), starter, alternator, ignition rinses and a few sensors are the same.

The displacement also invalidates the assessment of the peripherally revised engine. The new M-machine has exactly 2993 cm³, that of the X4 M40i is minimally larger with 2998 cm³. Because the bore and stroke also differ: 90 and 84 millimeters for the new M engine, 94.6 and 82 millimeters for the M40i machine. The shorter stroke was particularly important to the people of Munich, so that the pistons had to travel shorter distances and could travel at correspondingly lower piston speeds at the typical M speeds. The power increases linearly and reaches 510 HP (for the competition engine) from 6250 rpm – up to the maximum speed of 7200 rpm. The Competition holds the maximum torque of 600 Nm (in both versions) from 2600 to 5950 rpm, the 480 hp normal variant from 2600 to 5600 rpm.

Forged crankshaft, 3D printing for cylinder head

The shorter stroke design naturally also requires its own forged crankshaft. It is torsionally stiff enough for the high torque. The crankcase is constructed in the so-called closed deck design, which can handle high pressure well. Because the cooling jacket around the cylinder is not simply completely open upwards at the transition to the cylinder head, but rather is largely closed so that the seal is not only left to the cylinder head gasket. The iron coating of the cylinder liners in the arc wire spraying process (LDS) is said to save weight and friction losses.