There’s something special about a big six-cylinder engine under the bonnet of a large luxury sedan. True, today’s down-sized four-cylinder motors have closed the gap in terms of refinement, power and performance (while making a lot more financial sense), but they just can’t match the silky smoothness and lusty performance of a six. For some luxury car buyers, this extra bit of velvety bunch is an indulgence they don’t want to skimp on. It is this fastidious lot that these three cars we have with us today are out to please. Starting with the newest, we have the Mercedes-Benz E350 CDI that marks the return of a ‘big’ diesel engine on the E-class after an absence of over a year. Next up is the BMW 530d that got an update last year and brings in some straight-six thrills to the mix. Last but not least is the Jaguar XF 3.0d S that’s as desirable as ever, despite its 2009 year vintage. In case you’re wondering, we’ve left out the hugely capable Audi A6 3.0 TDI because it’s being slowly phased out in anticipation of a new one with updated styling and an upgraded engine, expected next year. Slotting into the gap between the mainstream four-cylinder variants on one hand and the manic V8 petrols on the other, these six-cylinder diesel engines have to be powerful and polished enough to offer convincing performance, refinement and a bit of economy. Engaging dynamics and all-round comfort are other aspects that will win (or lose) these cars points. So which one comes across as the most complete package? Two days of driving in Mumbai city and on the highway gave the answers.
Smashing six-es
Downsizing and making small engines do big things is the “in” thing these days, but it’s not that the traditional six-cylinder motor has been forgotten either. Take the 3-litre, V6, common-rail, turbo-diesel engine on the Mercedes E350 CDI, for instance. Sure, it’s the same engine on the older E350 CDI, but it’s been thoroughly revamped now to make it cleaner, greener and meaner. The last bit is taken care of by the not an insignificant 31bhp bump up in power to 262bhp, and rise in torque to a stump-pulling 63.2kgm. Thanks to these incremental increases in power and torque, the already quick E350 CDI has become quicker still. This one’s 7.09 second 0-100kph time betters the old car’s by half a second. It’s quicker through every gear too – the added pulling power has made the big Merc an even more effortless performer. To experience this, you need to see how readily the Merc pulls well past 140kph. But to me, the most remarkable thing about the engine is that it doesn’t make a song and dance about delivering smashing performance. Even with the throttle mashed to the floor, the decibel levels in the cabin don’t really go beyond a distant hum. It’s so quiet and relaxed that it’s easy to find yourself driving faster than intended – the E350 CDI masks speed brilliantly. For many, this engine’s superb refinement alone is worth the outlay over the E250 CDI, whose twin-turbo unit can be intrusive at times. Sport mode adds in revs (gearshifts take place at 4200rpm) and some more enthusiasm in the way the seven-speed automatic gearbox goes about its business. However, even here, the gearbox isn’t perfect. It lacks the immediacy of the competition’s eight-speed units and isn’t lightning quick when you use the paddles either. Interestingly, Mercedes recently introduced the E with a nine-speeder in countries that have adopted Euro 6 emission standards, but don’t expect that gearbox to come to India anytime soon.
Like the Merc, the Jaguar XF-S also uses a velvet-smooth, 3-litre, twin-turbo V6 diesel to power its rear wheels. Of note is this engine’s 270bhp output that makes the Jag the most powerful car here. However, it’s not the quickest. Though we could not test the latest version of the XF, it trailed the other two when dragged together. Some of that is down to the fact that the engine produces its 61.2kgm peak torque at a relatively high 2000rpm. To put things in perspective, the Merc’s peak torque band starts at 1600rpm while the bulk of the Bimmer’s pulling power comes in at an even lower 1500rpm. Also, throttle response is not as fluid as you’d like in slow-moving traffic. But give it some space and this engine is happy to show you its best side, starting with the terrific surge once the turbos kick in. There’s an almost unending reserve of power that will keep you pinned to your seat longer than you’d expect. Helping in no small measure is the fantastic eight-speed automatic gearbox that works beautifully to align the car’s performance with inputs from your right foot. The gearbox plays a big role in transforming the XF from a purring cat to snarling jaguar at your command.
The BMW 530d may use the same ZF-sourced eight-speed gearbox as the Jaguar, but in essence, it’s a very different car to its rivals. Where the Merc and Jag rely on V6s, the 530d’s 3-litre engine positions its six cylinders in BMW’s traditional in-line layout. Its 255bhp and 55kgm may put it down on power and torque to rivals, but it’s also the one that takes the ‘Sport’ in its name very seriously. Its sportscar-rivaling 6.1 second 0-100kph time is ample proof of that. It delivers strong punch from very low in the rev band, growls heartily to its limiter and is also the quickest-revving of the three engines on this test. Once again, the ever-ready gearbox gets a special mention here. It’s sharp on its own and obedient to well-timed inputs on the paddle shifters. But exciting as it is, the 530d’s engine is also perhaps too edgy for its own good. Throttle responses verge on the side of being overly sharp (even in Comfort mode) and this takes away from a seamless and smooth driving experience in everyday traffic scenarios. It’s here that you’d also wish the engine ran a bit quieter – the BMW is least successful in hiding the fact that there’s a diesel under the hood.
Rivan RS 
Viraaj Bhatnagar
Uday Singh
Suraj Viswanathan
