BMW’s move towards an entirely turbocharged range has been completed with the fifth-generation BMW M3 (and M4 coupe) debuting a twin-turbo in-line six to overtake the previous-generation M3’s naturally aspirated 4.0-litre V8.
The question remains over what that means for the future of the German brand’s iconic M division, which until 2010 had stayed clear of using forced-induction.
“I would say with the new [M] cars, all questions about naturally-aspirated engines are gone,” the head of BMW M division, Friedrich Nitschke, told CarAdvice at the M3/M4 launch in Portugal.
“I was absolutely a fan of naturally-aspirated engines and the decision [to go for turbo-charged engines] was not easy to make. The V8 was a fantastic engine and therefore our engineers had a big challenge to take a great car and make it a better one.”
The 4.0-litre V8 in the previous model M3 made 309kW of power and 400Nm of torque, which doesn’t compare favourably with the twin-turbo engine of the new car that pumps out a healthy 317kW and 550Nm.
Nitschke told CarAdvice the new engine brings the best of both worlds to BMW M cars, with the high-revving characteristic of the old V8 preserved, while the higher torque and fuel efficiency benefits of a turbo engine are realised.
Despite plenty of skepticism from both the media and BMW enthusiasts, the engine is winning over those that get to experience it, Nitschke said.
“You can imagine that a lot of our fans questioned [my decision] when they heard that we would bring a turbo engine [to the M3/4], I said please wait, test the car, drive the engine and then lets discuss.”
Although it may appear on paper to be a derivative of the ’35i’ twin-scroll turbo engines found across the BMW range, the BMW M3 and M4’s new 3.0-litre twin-turbo engine is substantially different and unique to the M Division.
The differences start at the core, with the M engine not sharing the same block as the twin-scroll turbo models. The M3 and M4 engine is a closed deck design with an entirely different philosophy to its normal counterparts.
The engine uses two Mitsubishi-made turbochargers that are mono-scroll and not sequential. The M engine is a true bi-turbo, with both turbochargers kicking in at the exact same time (both taking care of three cylinders each).
According to Norbert Siegl, project manager for the M3/M4 engines, the idea of an M engine is to be free revving and deliver torque across a wide RPM band, a hallmark of the previous-generation’s naturally-aspirated V8.
“I think it’s the philosophy of the engine and the car.” Siegl told CarAdvice.
“We try to deliver the torque and power over a wide range of rpm, that’s very important for us, if you look at the Series turbo engines, it only [revs] up to 5-6000rpm, then there’s no power, no torque and that’s not our philosophy”.
With a redline of 7600rpm, the new M engines are not shy of being revved, despite their turbocharging application.
Throughout its development phase, rumour had it that the new M3 engine might use three turbochargers, but Siegl says that was never the case.
“Tri-turbo is to push the pressure [higher] and that’s not our philosophy, our philosophy is to give torque at low rpm and do it over a wide rev range. That’s the philosophy of an M engine.”