A New 6.0-Liter Powerstroke Turbo Diesel For Towing Your Off-Road Toys

story & photos by Steve Temple

What’s a 1-ton diesel 4x4 Ford F-350 doing in an off-roading magazine? Isn’t that a little like reviewing a Budweiser Clydesdale’s agility on a narrow mountain trail? Well, yes and no. Those familiar with the lore of mountain men know there was a distinct place for the heavy haulers in the development of the mining and lumber industries in remote lands. That same heavy-duty function is now performed by a fleet of high-displacement, turbo-diesel pickups. These big boys may not be hauling lumber or machinery up the sides of mountains, but their cargo of exotic rock crawlers and other radically modified 4x4s can be just as valuable. So it makes sense to provide some details about advancements in diesel technology, specifically in Ford’s new turbocharged 6.0-liter V-8 Power Stroke.

Let’s face it, who among us wouldn’t rather cruise to our off-road Valhalla in the comfort and security of a plush yet torquey tow vehicle, especially one with 4-wheel drive capability? After all, just about everything we do to our 4x4s that enhances their off-roadability renders them somewhat less comfortable for an on-pavement drive to the off-road site. Still, there are the legions of civilized off-roaders who, believe it or not, use their vehicles to get to an actual destination (as opposed to looking for deeper dunes, steeper grades, slicker rocks, just for the sheer joy of conquering these obstacles). For those, however, who have the resources to tow their special-purpose, super-modified 4x4s behind a bigger rig, this stump-pulling Ford Super Duty is a great choice. It’s such a torquemeister, it wouldn’t even know anything’s back there, and you’ve got a four-wheeler with some creature comforts to boot.

Before we dig into the specifics of Ford’s new 6.0-liter turbo diesel, we should first cover a bit of background on diesels for the benefit of those accustomed to filling their 4x4s with gasoline. (Experienced diesel owners can skip to the juicy parts if they wish.)

The shortages and escalating prices of gasoline in the early to mid-1970s encouraged European auto manufacturers to introduce their diesel models to the United States. The efficiencies and lower fuel costs on the plus side never completely overcame the downsides of diesel engines for consumers. Diesels were heavier, slower (you didn’t really need a second hand on your watch to time 0 to 60 mph), the higher internal pressures meant more noise, vibration and harshness and the emissions left a lot to be desired. But that was then, and this is now.

Diesel engines have always been prodigious torque producers. Just look at the raw numbers. The 6.0-liter turbo diesel in this F-350 Super Duty comes in at 560 lb./ft of torque. Compare that hefty figure with the 250 lb./ft of Ford’s 5.4-liter V-8 gasoline engine, or even the 425 lb./ft with the larger 6.8 liter V-10. Torque is what gets us up and over obstacles at controlled speeds, and also hauls hefty loads of recreational gear, so diesel and off-road do indeed mix.

In what ways do diesels differ from gas-powered engines and how do they achieve these impressive torque numbers? At the risk of sounding like a Diesel for Dummies textbook, diesel fuel simply has more energy per pound than gasoline (about 17 percent). Diesel engines are more efficient because of this higher energy density — they produce more energy per volume, which translates into more pulling power and miles per gallon. No wonder all the long-haul 18-wheelers run diesels.

Every auto-shop student knows that both gas and diesel powered engines compress a mixture of fuel and air, which then ignites and drives the piston down. The difference is that diesel engines rely on super-heated air in the combustion chamber to ignite the direct-injected diesel fuel, while in gas-powered engines, that’s done with a spark plug.

The differences in engine design extend beyond the absence of the spark plug and its staff of support parts (wires, distributor, ignition coil, etc.) The diesel’s smaller head chamber allows the piston to super-compress the air/fuel mixture. For instance, the Ford 6.0-liter diesel’s compression ratio is 17:1, compared to the 9:1 ratio in the 6.8-liter V-10.

Of course, that makes for a distinctly different level of smoothness compared to a gasoline engine. Anybody who’s lingered at a truck stop for a while needs no further explanation. Still, the diesel engine has come a long way in the last 30 years.

With the new Ford Power Stroke, the noise, vibration and harshness (designated by the acronym NVH) have been reduced with design elements such as a rigid bedplate that stiffens the engine block and the block ribbing structure. There’s also a pilot injection system calibrated to reduce idle noise, and dampened steel covers and oil pans to reduce tranny noise. Plus the geartrain is at the rear of the engine to reduce gear noise and crankshaft torsional vibrations. Even with all these decibel-lowering refinements, behind the wheel of the F-350, you’ll still hear and feel conspicuous rattles at idle speeds (you probably should shut down the engine when you order a cheeseburger at the drive-through). At freeway speeds, however, the Blue Man drumming packs down to a mellower timpani (and somehow a truly quiet diesel wouldn’t seem quite right, anyway).

Interestingly enough, the smaller displacement 6.0-liter Power Stroke diesel rates better power and torque specs than the 7.3-liter it replaces, without losing anything in the durability department. The V-8 Power Stroke’s heart is a new cast-iron block and cylinder heads with a single, block-mounted camshaft in a compact overhead valve design.

In addition to doing more with less, the Power Stroke’s power rating, 325 hp at 3300 rpm, bests the 6.8-liter V-10 gasoline-powered engine (310 hp at 4250 rpm) thanks to its Electronic Variable Response Turbocharger (EVRT). EVRT employs a set of vanes that automatically adjust to optimize the airflow within the turbo.

For the uninitiated, turbochargers are forced induction systems that compress the air headed into the combustion chamber; more compressed air allows for more fuel, more power with each combustion — generally 30 to 40 percent more bang for your buck. Diesels in particular are ideal for turbocharging, partly because their stronger construction can handle it, and more importantly because it improves both power and fuel efficiency at the same time.

As with diesel engines, today’s technology is improving turbochargers as well. In the past, turbocharger enthusiasts had to choose between either smaller units that produced boost more quickly and at lower engine speeds, or larger systems that provided boost at high engine speeds (but with significant lag at the low end). The Power Stroke’s EVRT provides the best of both worlds by automatically adjusting its vanes to suit engine demands. It’s smaller in size for better fuel efficiency and altitude capacity, yet it also achieves better low-end response and reduces turbocharger lag more efficiently than the old-style wastegate system. Our on-road experience with the F-350 revealed a fuel consumption figure as high as 25.6 mpg on the highway, and 16.4 mpg around town. In both cases the vehicle was only lightly loaded and running at sea level, so those are somewhat idealized numbers.

The fact that the Power Stroke is turbocharged is meaningful to off-roaders in a couple of ways. The beefy torque rating is significant when the F-350 is being used as a tow vehicle, and the strong performance comes into play on steep dirt grades. The shift-on-the-fly system makes alternating between two- and four-wheel drive literally a push-button proposition.

Eco-friendly off-roaders will be glad to hear that the 2003 Power Stroke meets federal emission regs ahead of schedule with a cooled exhaust gas recirculation (EGR) system that reduces the NOx emissions by 20 percent. A portion of the exhaust gasses are directed through a cooler and reintroduced into the engine combustion chamber. This process controls the combustion temperature, a big step in reducing conditions that lead to the formation of NOx. And the good news is that the system does this without negatively impacting performance or fuel economy, while older systems met emission standards by delaying the injection timing.

Ford also built a new automatic transmission to handle the higher-powered 6.0-liter diesel: the TorqShift, a five-speed with improved gear ratios (a lower low and higher high) and a cooling system that lets the tranny run 50 to 70 degrees cooler — a big plus for durability.

For the kind of terrain 4x4 enthusiasts generally prefer, the big plus for the TorqShift is the driver-activated tow-haul mode, which results in more controlled shifts when the F-350 is towing a trailer loaded with dirt bikes or a rock-crawling 4x4. Headed uphill, the tranny holds a gear longer to maintain consistent travel. No more confusion on the transmission’s part as it tries to reconcile travel speed and load on the engine. Downhill, the driver taps on the brakes to signal the tow-haul mode to downshift when appropriate to slow the vehicle. The engine slows the vehicle rather than the brakes for vastly improved control over both the tow vehicle and the load.

The bottom line is that diesels make sense for all sorts of excursions. Unlike the old days of lumbering lumber trucks, improved technology means that Ford’s Power Stroke is well suited for the grunt and grind encountered in just about any off-road adventures.