It is often said that the BMW 320d is all the car most of us will ever need, and that's certainly true of the current G20 version. It's economical, comfortable and, when you choose to wring its neck, enjoyable to drive. Only its fuel-sipping motor could really be said to leave you wanting more - and (as ever) that's where the 330d steps in, replacing a shy and retiring four cylinders with a commanding and torque-laden six.
Like the other M Sport G20s, this 330d comes finished wearing sportier trim and a set of 19-inch alloys, wrapped in Michelin Pilot 4S rubber. But Plus trim builds on those specs further with adaptive suspension, an M Sport differential and more powerful M Sport brakes. Inside, it's been kitted out with BMW's top-spec 7.0 cabin operating system and head-up display, among other things, resulting in an on the road price of £51,605 - more than £10k up on an entry-level 330d. Chances are that'll make it pricier than the incoming Audi S4 TDI, too, which gets its maker's Virtual Cockpit system and more power as standard.
We know BMW's inline diesel motor is a very good one, though, and in the 330d it produces a not to be sniffed at 265hp and 428lb ft of torque alongside around 47mpg of combined economy and 157g/km CO2. It'll do 0-62mph in as little as 5.5 seconds, but really it's about the arrival of all that twist at 1,750rpm and the smooth, surging hustle of a BMW-made multi-cylinder engine. We've driven the 330i recently, too, and while it doesn't want for accelerative effect, it is the four-pot petrol motor's shortfall in refined, middle-order shove that distinguishes it from the superior feel of a proper engine.
The oil burner is well matched to the G20's high-calibre chassis. When pressing on there's gravelly pleasure to be had from the six, but with everything set to Comfort there's precious little in the way of road, wind or powertrain noise when you want it to be quiet. With the dampers relaxed, the M Sport glides along B roads with the eight-speed auto content to leave the engine's wide torque window to do all the lugging. Click through to Sport and everything sharpens up as you'd expect, although the damping still allows for enough vertical movement to soak up imperfections. Ultimately you'll want to put the steering back into Comfort mode thanks to the gloopy resistance - but that's par for the course.
Throttle response is very good and the engine, while somewhat breathless above 4,500rpm, rotates so energetically within its productive range that it never feels like it's been scalped. Significantly, the motor's pace feels well matched to the damping, which makes for a reactive front end but doesn't leave the car short of cushioning into dips or loose over crests. Maybe it's the added weight of a 3.0-litre unit up front enhancing the mechanical grip of those Michelins, but the 330d swaps directions brilliantly well, with a nicely neutral balance inspiring you to hammer into corners and maintain momentum rather than relying on the engine to lug you out. There's just about enough torque for it to be adjustable under throttle, too, with the diff happy to oblige the more enthusiastic peddler. And rather than bogging down there's enough grunt left over to keep those back wheels pushing on to make the process fluid, something that's heightened by the consistency of the chassis's footing over changing surfaces.
It's all properly convincing stuff, and while we're not going to proclaim the 330d as some sort of black pump-quaffing sports saloon, it speaks to the superlative job done on tuning the car to make the most of its obvious strengths. The limit of enjoyment is mostly to do with the fundamental limitations of what a diesel engine will realistically do - within that threshold, the car is probably as entertaining as anyone could expect it to be. The fact that it does that with the authentic rear-driver character and no little refinement helps the G20 to stand particularly tall. Just as the Audi S4 TDI-shaped elephant is about to enter the room.
SPECIFICATION - BMW 330d M SPORT PLUS
Engine: 2,995cc, six-cylinder, turbo
Transmission: eight-speed automatic, rear-wheel drive
Power (hp): 265@4,400rpm
Torque (lb ft): 428@1,750-2,500rpm
0-62mph: 5.5 seconds
Top speed: 155mph
MPG: 46.3 - 47.9