Big diesels - Dodge's Cummins and Ford's Powerstroke

We're going to do a 180 now, as our last feature focused on a pair of high-revving V6s. The two engine we're going to look at here are anything but. However, let it not be said that they aren't impressive in their own right.

Until GM grabbed the Duramax from Isuzu a few years ago, there were only two names that needed to be considered when talking about heavy-duty light-truck diesel power - Cummins and Powerstroke. While the Cummins has been through some revamps and the Powerstroke was completely redesigned for 2003, both engines maintain a fierce loyalty that goes beyond the nameplate of the truck in which they're installed. In fact, it's nearly impossible to overstate the importance of these engines in this particular segment of the market. Let's dive right in and see what makes these engines tick (or is that 'clatter and roar?').

We'll start by taking a look at the B-series inline-6 Cummins turbodiesel that's currently available in heavy-duty Dodge Ram pickups. This engine was developed by Cummins and Case for medium-duty truck applications in the 1980s, and adapted to the Ram for the 1989 model year. Sales of the powertrain option quickly outstripped projections, and today it's hard to imagine the Ram lineup without the Cummins (somewhere around 70% of Dodge 3/4- and 1-ton pickups are equipped with the oilburner).

Due to its commerical vehicle roots, it's not really even fair to say that this engine is "overbuilt". Look up the word "robust" in the dictionary, and the Cummins logo appears.

Gear-driven cams are something we usually only expect to see only on the racetrack. In this case, it's in an engine that perhaps has the lowest redline of any powerplant sold in the US. The crank directly drives the cam, which in turn drives the injection pump located at the right side of the above picture. The extra noise of a gear drive system is inconsequential on a diesel, and there's no doubt that it's the most robust way to make stuff spin for a half-billion or so revolutions.

Here's the Holset turbocharger that's used to produce the Cummins' impressive output. Take away the boost, and this engine produces maybe all of 150 HP. Add more fuel and boost, and become good friends with your favorite transmission shop. Note the lack of a variable-vane turbocharger.

Here is where the Cummins has made its reputation. The picture doesn't do justice to the size of the componentry in the bottom end of this engine; the connecting rods simply dwarf those of a standard small-block V8. Keep in mind that each cylinder displaces nearly a full liter. Reciprocating weight is of little concern, as withstanding the incredible combustion pressure of a turbodiesel is the order of the day. Note the deep-skirt block, which was used on diesel truck engines decades before it become the popular thing to do on automotive engines.

Don't be fooled into thinking that there's a lack of engineering sophistication, however-- note the angle of the cap split on the bottom end of the connecting rods. Most rods will have the split at 90 degrees to con-rod beam, but the Cummins engineers rotated the parting line approximately 30 degrees to better-center the bearing loads during operation.

The current trend in piston design is towards short skirts, as to reduce friction and weight. That trend won't be found here. I wouldn't be surprised if the long-skirt design actually caused a reduction of friction in this application.

In this common-rail direct injection system, fuel is squirted at the top of the piston by a centrally-located injector. Yep, there are actually four valves per cylinder, actuated by pushrods.

Normally, at this point we'd tend to talk about intake and exhaust port geometry, but there's just not much to discuss on most truck diesels. If one needs more power, there's always the option of more boost.

Engine-mounted ECMs (electronic control modules) are another current fad on passenger-car engines that has been standard fare on truck engines for quite some time.

The large base diameter of the "flat" lifters makes life easier for the camshaft. Rollers would reduce friction, but add complexity.

 Fuel filtration is important for any diesel, due to the pump tolerances required to achieve 20,000 PSI of rail pressure. Most passenger cars have a smaller oil filter than this engine's fuel filter.

Ford has had a variety of Navistar-designed diesel engines throughout the years, starting off with the 6.9L indirect-injection V8 in 1983, which was then replaced with a 7.3L that ran until 2004 in some applications. In 2003, the 6.0L Powerstroke was introduced to significant fanfare due to its impressive power output. Unfortunately, however, it has been plagued by several reliability problems.

Compared to the 7.3L, the accessory drive of the 6.0L Powerstroke appears cleaner and much more compact.

The turbocharger is mounted in the valley of the engine, which is about as close to optimum as one gets for a single turbo on a V-type engine (the plumbing involved in getting the exhaust from both cylinder banks up to the turbo and then back down to the rear of the engine is rather complex and bulky).

The engine's control module is mounted on the left valvecover; it's the dark-colored box at the upper-left of the photo.

Here's another gear-driven camshaft, this time at the rear of the engine. That's highly unusual for a V8 mounted in the typical fore-aft manner. Roller lifters are used on this engine.

The rockers are constructed from heavy steel stampings. A single in-block cam drives a total of 32 valves. The log-style exhaust manifold isn't exactly sexy, but optimized cylinder scavenging becomes a non-issue with the backpressure of a turbocharger.

This picture gives us a good view of the centrally-mounted injector, which is fed by from a common rail. Ford refers to these injectors as HEUI - Hydraulically actuated Electronically controled Unit Injectors. Engine oil is pressurized and used to control the injection of fuel via an intensifier piston; high-voltage solenoids control the application of oil and thus ultimately how much fuel is injected. The system does away with high-pressure fuel pumps, but unfortunately the use of the engine's lubricating oil means that engine performance can be affected dramatically by the oil condition.

This is not the sort of intake port geometry that would make one swoon if observed on a gasoline engine, but sexy-looking cylinder heads do little good in the average operation range of most diesels. 

We're back to the turbocharger once again. The Y-pipe at the lower left of the above photo is the incoming exhaust plumbing from the manifolds. The exhaust exits via the center of the turbocharger's turbine; at the lower right.

A closer look at the turbocharger reveals variable vane geometry. An actuator, at the left-center of the above photo, is used to rotate a cylindrical plate (the chrome-plated ring that's viewed between the two blue-painted walls). This in turn alters the geometry of vanes that direct airflow onto the turbine. The advantage of variable-vane turbochargers is that they allow optimization of compressor response across a wider range of operation, and thus makes for a flatter and more usable torque curve.

So, there's a brief comparison of what are actually two very different engines. We'd have liked to thrown in some pictures of a Duramax, but alas, we don't have any photos of a cutaway to reference.

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