BMW's new M engine needs a better voice

BMW's M division claims its new twin-turbocharged 3.0-liter inline six-cylinder engine is every bit as good -- if not better -- than the glorious, naturally aspirated 4.0-liter V8 powerplant it replaces in the new M3 sedan and M4 coupe. The figures are certainly impressive. They say it kicks out 424 hp and more than 25 percent extra torque, with what is described as significantly more than 369 lb-ft below 2,000 rpm.

No lack of grunt, then. But as I sit next to Martin Tomczyk -- one of a trio of factory drivers BMW's M division has brought to the unveiling of the new engine at a test track north of Munich -- in an M4 coupe prototype mule ready to head out for a couple of hot laps, I'm not so sure the move to forced induction is going to be met with quite the same enthusiasm as that shown by the men from BMW M.

Get the full story on the new BMW M straight six engine here

The sound of the new engine lacks the sheer intensity of its predecessor, both mechanically and in the sound of the exhaust. As Tomczyk, a former DTM champion, fires the camouflaged coupe off the line with a heavy dumping of the clutch and a big dose of right foot, the primary aural accompaniment is an uncomfortable whooshing of the turbochargers -- a pair of IHI units operating at a maximum 1.3 bar of boost pressure. Up into second, third and fourth gears, I detect a rising in the rate of revs, but whereas the mechanical attributes of the engine used to be a headlining act, they are now a distant play in the driving experience.

Down the slip lanes and through a series of witches hats at speeds touching 100 mph, the revs rise, then fall, but the exhaust note remains disappointingly flat. The BMW M division has developed a new cross-flow muffler with flaps that open to direct the exhausts straight to the tail pipes at higher engine loads. It is supposed to enhance the sound. However, it fails to endow the new M4 with anywhere near the aural force of the old M3 coupe. The M4 prototype could well be a regular 435i with an M-Sport exhaust, or so it sounded. When we return to the staging area, I let my feelings be known to a group of engineers. I'm told the engine lacks the latest developments, which comes as a bit of a relief. I can only hope the production car, due to go on sale in North America in May, sounds better. With such pedigree, it ought to.

By Greg Kable