Diesel love affair

While out of town a few months back, our host was wondering aloud why people buy a very expensive vehicle and opt for diesel propulsion instead of gasoline engines in the interest of saving on running cost. Gasoline-powered engines also sound better, feel smoother and more refined, while offering that exciting top-end lunge on the race track or on the highway, or so he says.

This got me thinking, as I love diesel-powered vehicles. I thought about it and realized that, call me a cheapskate if you will, but any savings that can be had while driving fast gives me an added smugness about the entire package. Previously, diesel engines were noisier than a 9-Inch Nails/Black Sabbath/Rod Zombie concert all rolled into one, blew out as much smoke as Biblical Beast and smelled like Chemical Weapons had bombed the Metro. In short, diesels were perceived to be evil. The limited power-band also didn’t help the driving enjoyment, even with turbocharging added into the mix.

Most modern diesel engines feature common-rail direct injection and turbocharging. The more advanced CRDi diesel engines also offer variable geometry turbines which alter the turbine and/or compressor wheel blades to flow both intake and exhaust gasses better, depending on the engine speed and load. Direct injection alone, be it on diesel or gasoline-powered vehicles reduces pumping losses on an engine, an increase in efficiency by as much as 12 percent and reduction on emissions by an even greater amount.

Plus I love the torque afforded by turbocharging. I’ve had the pleasure of driving a vast array of high-end automobiles in both gasoline and diesel engines. I’ve always had more fun in the diesel variants because the g-force is immediately available from the get-go, providing instant, ear-to-ear satisfaction the moment you get on the loud pedal (i.e. the throttle or accelerator), except that things don’t get loud, they get eerily turbine-like swooshy. Better to escape and avoid attention.

The Audi A6 and A8, the BMW 7-Series, X1 and X3, the Mercedes-Benz ML and GL Class SUV’s, all these high-end German automobiles offer diesel engines which really bring out the best in them. Saddled with a relatively heavy weight, gasoline engines, even V8’s, need a good amount of revs for things to get exciting. With diesels, the first thousand or so RPM’s from idle instantly lunges these big heavy luxo-barges into serious speeds without the fuss and histrionics of a gasoline-powered engine. Makes sense then that more and more high-powered, high-caliber and low-profile individuals are opting for diesel-engined luxo-barges. It is the automotive equivalent of having your cake and eating it with gusto.

Let’s look at the numbers. A typical 3.5 liter V6 gasoline engine produces anywhere from 265-300 hp and about 300-360 Newton-meters of torque with a redline of about 6500 rpm. Audi’s turbocharged 3.0 liter V6 produces a low 240 hp but a monumental 500 Newton-Meters of torque from as low as 1500 rpm to practically its low redline of about 4500 rpm. Any experienced racer, engine builder and tuner will tell you that horsepower sells engines but torque wins races, as evidenced by Audi’s 10 victories at the Le Mans 24 Hour Endurance Race. Typical real-world fuel economy for the aforementioned gasoline engine is about 5.5 km/liter in the city and as high as 10 kilometers per liter out on the highway, nudging at a constant 120 km/h (the maximum allowed tolerance for speed by law enforcers to take into account speedometer calibration errors common on cars).

The Q7 3.0 TDI is able to consume about 7.5 km/liter of fuel in the city, and as much as 14 km/liter out on the open highway at the same speeds. The Q7 is bigger, heavier and has greater coefficient of drag, but is more fuel-efficient. As for running cost? The cheapest unleaded gasoline from the big three is well over P50 per liter, whereas the premium diesel fuels are still cheaper the last time I checked. So you’ve got savings there as well.

As for top speed? A friend’s previous generation Audi A6 3.0 TDI was able to achieve a constant 240 km/h before the cops nailed his speeding ass on SCTEX. There are fuel savings in motorsports as well. A typical top-class GT1/Sports Prototype racer in Le Mans can do about 12-13 laps before needing to pit in to refuel around the 8.5 mile La Sarthe Circuit. The Audi R18 diesels can achieve easy 14-15 laps before pitting in. Considering that an average race lap around Le Mans is about 3 minutes and 28 seconds, imagine the lead it will make after 100 laps. And these diesels still nudge close to 380 kph on the fearsome Mulsanne Straight.

Are diesels slow? Ask Audi, BMW, Mercedes-Benz. In fact, ask Hyundai, KIA, Mitsubishi, Toyota, Nissan and Isuzu, brands which revolutionized affordable CRDi and VGT engines making them more affordable to the everyday man. So everyday man can go fast and save himself lots of money.