There have been other 100-plus-horsepower-per-liter engines to win past Ward's 10 Best Engines awards, but none has enjoyed the staying power of BMW AG’s magnificent 3.2L DOHC I-6 “M” engine.
Credit one thing: BMW’s stalwart inline architecture.
To make in excess of 100 hp/L inevitably requires a high-rpm power peak. Internal combustion engines essentially are air pumps – the more air one can “move,” theoretically the more power one can produce. Moving lots of air typically requires lots of rpm. Ask those Formula One engine guys, who squeeze out hundreds of horsepower per liter, if you don’t believe us.
Past engines that have enamored us in the specific-output stakes eventually have proven to be rather “boring” one-trick ponies. Revving a 4-banger to 9,000 rpm – in each and every gear, all the time – inevitably becomes a grating chore to extract, say, 80% of an engine’s power. Few engines genuinely reward perpetual redline visitation.
|Stunning power and smoothness from BMW 3.2L DOHC I-6.|
BMW’s always-spectacular 3.2L DOHC I-6 is one, however. The inherently balanced inline 6-cyl. layout, so marvelously refined by BMW over the past four decades or so, virtually rejoices in bouncing the tach needle into the scarlet.
Equally important, you the driver enjoy it, too, because even with 103 hp/L, the 3.2L “M” engine gives no quarter to demons of ill-refinement. Spin this engine with disdain, and it responds with nothing but the same velvety demeanor whether turning 3,500 rpm or 7,000 rpm. “Thrashy” simply is not in this engine’s vocabulary.
And who couldn’t smile at the notion of six discrete throttle bodies – one for each cylinder – toiling at your whim? Or better yet, the “M Driving Dynamics Control” electronic throttle control that allows you to select an almost laughably sensitive setting for those six trumpets? It’s a sublime engine-management trick that, frankly, we’re surprised has yet to be replicated – or upstaged – by any competitor.
The 3.2L DOHC I-6 still represents the pinnacle of BMW engineers’ development of the I-6 format.
Although some of its technology-showcase starpower has been eclipsed by the company’s Valvetronic V-8/V-12s and even direct-injection technology, the inline 6-cyl. layout, which BMW says would be foolish ever to abandon, continues in this variant as BMW’s ultimate – and ultimately most significant – expression of its heritage.
|BMW AG 3.2L DOHC I-6|
|Engine type||3.2L DOHC inline 6-cyl.|
|Block/head material||cast iron/aluminum|
|Bore x stroke (mm)||87 x 91|
|Horsepower (SAE net)||333 @ 7,900 rpm|
|Torque||262 lb.-ft. (355 Nm) @ 4,900 rpm|
|Specific output||103 hp/L|
|Fuel economy |
for tested vehicle
(EPA city/hwy. mpg)