I’ve been intrigued by the idea of diesel engines for cars for a very long time. I was still in high school when the impressive Cummins Diesel Special’s took the pole at Indianapolis in 1952, suggesting a revolution in the making. But it actually took more than half a century before a diesel engine would win a major motor race. Ten years after the Cummins achievement there were two diesels on sale in the US, from Peugeot and Mercedes, both of which liked to claim that they were first to offer production diesels in their home markets, although a Citroën Rosalie wagon preceded them . They were noisy, smelly, slow and tedious to operate: you had to wait for an interminable period (well, actually just a minute, but it felt long) for a glow plug to heat up the combustion chamber so the engine would light off, and when you wanted to stop, you had to pull out a plunger that did something to cut fuel flow.
In 1968, I spent almost a month driving around Europe in a Peugeot 204 station wagon equipped with a small (1255 cc) high-speed (5000 rpm) 46 bhp diesel. It was still noisy, smelly and slow, but also fairly nimble and certainly extremely economical. That experience led me to write a piece praising the possibilities of diesels in a 1969 issue of Motor Trend, in which I made the controversial suggestion that should diesels ever come in America, they should be in Cadillacs, air-conditioned and fitted with automatic transmissions to hide the fact that diesels did not accelerate well, and were all out of revs very early, requiring a driving technique antithetical to US habits.
During the last ten days or so, I’ve had a crash course in the latest diesel technology, or at least part of it. First was a seminar at the Mortefontaine test track north of Paris, where Renault showed off its latest 130 bhp diesel, a 1600cc four-valve four cylinder engine. It replaces a 1.9 liter engine of the same power, but saves 20% of fuel and almost — but not quite — qualifies for a bonus for low CO2 emissions. The design leader for the R9M project, Philippe Coblence, held the same job at Renault’s Formula One operation when the company developed its championship-winning V-10 engines.
Using only 25% of carryover parts from earlier 2.0 liter fours and 3.5 liter V-6 diesels, the new 1.6 liter, four-cylinder, four-valve DCI 130 engine develops the same power as its 1.9 liter predecesor, weighs no more despite the addition of numerous poullution-reducing accessories, and is both quieter and noticeably better in drivability. Drawing on F1 practice, it is a “square” engine, with more and stroke close to identical, giving more surface area for bigger valves.
Just a few days after driving the Renault engine, I was in Barcelona to try the newest Citroën crossover, called DS 4. A fairly clumsy car intended as a combination crossover-SUV-sedan, it was tuned to be “sporty” in gasoline form, with a rorty exhaust sound that was quite quickly tiring. When my French colleague and I tried the same car with its diesel engine we found it far more pleasant to drive. With the same tire-wheel combination, it had plenty of grip, but we were spared the exhaust noise and the need to change gear as often – the massive torque of the diesel making for a more relaxed but equally quick run. The gasoline engine makes 275 newton-meters of torque between 1700 and 4500 rpm, while the 40 bhp less powerful diesel churns out 340 Nm between 2000 and 3000 rpm.
But the real clincher that diesels are really here as superior automotive powerplants comes from driving a couple of thousand miles in a BMW 530d, a three-liter, 245 bhp diesel that used a lot less fuel than a two-liter Renault I owned a few years ago and used on a similar run in Italy. Driving from Paris to the Dordogne, to Geneva and on to Lago Como, I could set the cruise control at whatever speed I liked and the car would hold it effortlessly. The wind noise was greater than the engine sound, and there was very little of either. The BMW is, thankfully, not Lexus-quiet, but always assures with the subdued sound of well-engineered machinery. To cruise for hours at a legal 82 mph while getting 33 mpg is really satisfying. Knowing that you could push the speed up to 140 mph effortlessly is really reassuring. The same engine, in a different state of tune, is offered in the 535d where it makes 306 bhp, gets to 62 mph in less than 6 seconds and — at least according to BMW France’s PR leader — uses no more fuel in normal driving.
Hybrids, electrics, fuel cells, all the techniques being explored for daily drivers are worthy experiments, but for right-now use, European-standard diesels will beat anything else on American roads. Sure, you can go faster with a supercharged 7 liter V-8, but not legally, not on public roads. I really don’t hold much brief for diesel racing cars now, but I surely am impressed by what can be accomplished with a multi-valve, electronically-controlled, catalyized low-pollution compression-ignition engine in normal sedans, wagons and SUVs.