Archive: Volkswagen Golf and BMW 3-Series petrol vs diesel

First published in the January 2011 issue of Wheels magazine, Australia's best car mag since 1953.

Is a good sports diesel a good sport, full stop? Golf and 3 Series oilers take on their petrol siblings to see which really provides the spark.

THE TERM ‘sports diesel’ is oxymoronic no longer. Back in the dark days, oiler power was reserved for load-lugging tractors which demanded torque. Then, some boffins came along and took the compression-ignition engine to finishing school. High-pressure ‘common’ rails that inject fuel directly into each cylinder increased efficiency; finely-tuned piezo injectors which vary fuel-spray loads reduced combustion noise; and particulate filters cut down exhaust soot.

From 2005 to 2008, diesel passenger car sales in Oz quadrupled to 19,791. When green-tinged eco-diesels like the Mini e and Ford Fiesta Econetic began appearing, the oiler was no longer seen as dirtier than a Kings Cross strip club. And when Audi and Peugeot started winning LeMans with diesels, it was only a matter of time before oilers gained enthusiast appeal. Many have tried … and failed. The rattly acoustics of a Pug RCZ HDi ruled it out; likewise the narrow powerband of the now-superseded Renaultsport Megane 175 DCi. Audi’s A5 3.0 TDI boasts cracking performance, but an anchor-heavy front end.

Enter the BMW 330d and Volkswagen Golf GTD – the first sports oilers that right most diesel wrongs. But can they stare down two of the best petrol-fuelled sports cars in the business, their very own 335i and GTI siblings? We’ll assess the real-world elements of price, economy, emissions, servicing costs and resale, then apply the blowtorch on the strip and in the twisties to see if diesel, finally, can fuel our fire…

BMW 335i vs 330d

Sports coupe twins fuelled by different flames; split by a cigarette paper.

LINED UP on the dragstrip either side of the Christmas tree lights, the 3 Series Coupes appear identical. Black paint, lowered M Sport suspension, 19in alloys filling the guards. Only an A-grade trainspotter will pick them apart – the BMW 335i has split exhausts and five-spoke wheels, the 330d twins and 10-spokers. Both boast Euro V-compliant 3.0-litre all-alloy single-turbo sixes, tied to a seven-speed dual-clutch ’box for the petrol and six-speed ZF auto for the oiler.

The petrol 335i plays its ace with an extra 45kW (225 versus 180) but the 330d uses its greasy tactics to full effect with a 120Nm trump card (520 v 400). The oiler leaps off the line first, and is three-tenths ahead to 60km/h, at 2.7sec. But the auto’s slurring 5000rpm upshifts pale against the dual-clutch’s bullet-quick cog-swaps. By 100km/h the 335i snatches the lead by two-tenths, at 5.7sec, the top-end power doing its best work. It crosses the quarter at 14.1sec – an identical time to the 330d but a full 6km/h faster.

There’s no avoiding the elephant in the room, though ... aural appeal. With only a hint of clatter at idle, the BMW diesel is creamy on light throttle, rising to a distant growl when pressed. But the petrol six sounds better. Snarly and raunchy, it strums out an epic power chord that is addictive.

Still, there isn’t much in it, especially considering the $120,200 335i M Sport costs $21K more than a 330d M Sport. Both models have condition-based servicing, and BMW claims they’ll each require six services and will cost around $5800 over 100,000km. The 335i will retain more of its (higher) purchase price after three years – 59 percent versus 55 – but loses more ground in the economy stakes.

On the freeway the 335i guzzled fuel at almost double the rate of the 330d, returning 11.1L/100km compared to the frothy oiler’s miserly 5.8L/100km. Up the pace, and both cars’ fuel use soared to 18.4L/100km (335i) and 12.4L/100km (330d). The 330d also pumped around 110g/km less CO2 into the atmosphere whether carving corners or cruising. However, burning oil produces much more smog-creating NOx than petrol. BMW claims the 330d outputs a staggering 13 times more oxides of nitrogen than 335i – 132mg/km versus 10mg/km.

It matters little which engine is up front when it comes to dynamics. Both boast crisp turn-in which transitions into sublime rear-drive balance. Fact is, the 335i is more manic and exciting, though the 330d never falls behind, and can pull away from the 335i on tight uphill switchbacks by virtue of its extra torque. Call it a dynamic dead heat.

All of which means the 330d matches the more expensive 335i for performance and handling, and hammers it for economy. Only your ears will miss the wail of the petrol six. Consider it a (qualified) win to the sports oiler. Rudolf Diesel would be stoked.

Volkswagen Golf GTI vs GTD

Oil’s well in a hot hatch? Not when a petrol all-star is on your tail.

THINK OF the automotive equivalents of ’90s Brit-popsters Posh and Sporty Spice and you’ll understand the Volkswagen Golf GTI and GTD siblings. Both hail from the same band, with subtle differences in image and personality. The diesel GTD dresses in more formal attire, with a chrome grille and polished alloys; the petrol GTI wears a louder tracksuit with red lip-gloss and brake calipers, split-twin exhausts and 7mm-lower front suspension. In five-door six-cog manual form, Posh costs $39,290, Sporty $40,490.

Both are a litre and two pots down on the BMW coupes. GTD’s 2.0-litre turbo-diesel four gets all the latest gear like common-rail direct injection, with nozzles that spray varied fuel quantities depending on load.

Typically for a diesel, the GTD is a big torquer, with 350Nm on tap from 1750-2500rpm. However, the same-capacity DI turbo petrol GTI’s lesser 280Nm is offered over a wider 1700-5200rpm plateau, until the full 155kW takes charge from 5300-6200rpm. GTD will happily rev to 5200rpm, but its max 125kW peaks at 4200rpm. A full second separates the siblings at 100km/h and 400m: 7.0sec and 14.9sec GTI; 8.0/15.9 GTD.

The VW diesel sounds like a woofy old-school, carby-fed four, but with a more refined edge, while the petrol is classic GTI – whipped-cream smooth, zingy, with a particularly tasty exhaust pop on overrun.

Slip each car’s Brylcreem-slick manual into sixth on the freeway and both are quiet. The GTI’s low-rpm torque means there’s no need to chase revs on hills, easing boost and therefore consumption. It returned an excellent 6.5L/100km, one-third more than the GTD’s 4.9L/100km, at an extra cost of $2.60 per 100km.

Regularly spin the GTI’s crank to 7000 revs, however, and consumption soars to 15.5L/100km. In parallel with the 3 Series, on the same ‘dynamic’ test route, the petrol GTI slurped 50 percent more fuel than the diesel GTD, meaning an extra $8 per 100km. Also like the BMWs, the diesel emitted less CO2 on test, but the GTD’s (near-equal to 330d) 131mg/km NOx output is far worse than GTI’s (five times higher than 335i) 49mg/km.

Unlike the two BMWs, though, there is a clear difference between the Golfs’ dynamics. The oiler’s cast-iron block (unlike the 330d’s lighter all-alloy variety) and tougher internals place more weight over the GTD’s nose. In isolation, it’s still typical Golf – ace balance, rock-solid composure, stacks of fun. However, by comparison the lower-suspended GTI feels darty at the front-end, engaging and dancing with you in a way the heavy-footed diesel can’t.

Consider the GTD’s $1200 saving up front in addition to its $340-cheaper servicing costs over 100,000km and 30-to-50 percent fuel saving, and the oiler makes good financial sense. But it isn’t as quick or sharp as a GTI, and for true enthusiasts, that still makes petrol power worth the premium.