The Rise of Diesel: Why Compression Ignition Has Become So Popular
If you’re buying a ¾-ton, 1-ton or larger pickup in 2020 and you don’t take the diesel option, you are overwhelmingly in the minority. Things weren’t always this way, though. Back in the '80s, diesels were smoky, underpowered, cold-blooded and consumers generally steered clear of compression ignition. In the '90s things began to change. Not only did they come with more power but they ran cleaner. As diesel technology continued to advance in leaps and bounds (think electronic controls and common-rail injection), their signature, teeth-rattling clatter was quelled and power ratings continued to climb while tailpipe emissions kept trending downward. Below, we’ll discuss why diesel is so appealing to the truck-buying masses from an OEM perspective, but also from an aftermarket point of view.
OEM Perspective
Direct Injection
Other than the fact that it came with a turbocharger (the competition from GM and Ford at the time did not), the 5.9L Cummins was the first diesel to feature direct injection in the diesel truck segment. With this form of injection, there is no pre-chamber or mixing of fuel and air before combustion, fuel is sprayed directly in-cylinder and the combustion chamber is present in the top of the piston. Thanks to its higher operating pressure, direct injection is more efficient than indirect injection, which culminates in considerably more performance potential, better fuel economy and lower particulate matter emissions.
Electronic Controls
In 1994, Ford debuted the 7.3L Power Stroke, its first direct injection diesel but also its first diesel with a fully electronically controlled injection system. The ability to vary injection timing and injection pressure independently from engine speed made for more precise control of emissions and offered improved drivability. It may have been primitive in design, but this wouldn’t be the last time an electric current was sent to a solenoid-equipped injector in order to fire it. Actually, it was only the beginning.
High-Pressure Common-Rail
Once electronic control was combined with direct injection and quicker-firing, multiple-event injectors, diesels were never the same. In 2001, that happened when GM’s 6.6L Duramax introduced the truck world to high-pressure common-rail injection. In this arrangement, the high-pressure fuel pump (i.e. injection pump) pressurizes the low-pressure fuel it receives from the tank to more than 23,000 psi before sending it to the fuel rails, where it’s stored until the injectors are called upon to fire. In addition to this high pressure system making a common-rail engine squeaky clean and incredibly drivable, pre injection events (called pilot events) can precede the main shot, significantly muffling the noise and vibration older diesels are known for.
Lack of Turbo Lag
Variable geometry turbocharging first infiltrated the ranks of diesel pickups in 2003, with the Garrett GT3782VA sitting in the valley of the 6.0L Power Stroke. By restricting exhaust flow through the turbine side of the turbo, a VGT will act like a much smaller charger off idle and at lower rpm to help get the load moving. At high rpm, full exhaust flow is permitted across the turbine, the result being that the turbo feels like a larger unit. VGT technology made turbo lag much less of a worry than it had previously been and offers responsiveness at any engine speed.
All of the Above = Powerful, Highly Refined and Fun to Drive
Add it all together—direct injection, electronic control, high-pressure common-rail injection and variable geometry turbocharging—and you get the trucks we have in 2020. They’re eco-friendly, perpetually in whisper mode and the most powerful engines their respective manufacturers offer. The weakest torque number of the lot is GM’s L5P Duramax (shown), which still spits out an insane 910 lb-ft in factory trim. The smallest horsepower figure is owned by the new 6.7L Cummins at 400 hp—but its 1,000 lb-ft of grunt means it’s not exactly playing second fiddle.
Aftermarket Perspective
You Can Make Huge Power
The advent of electronically controlled diesels ushered in the age of easy horsepower. Taking advantage of the beefy internals and extreme injection pressures a modern diesel engine employs, most late-model versions can pick up an additional 150hp with nothing more than a programming change. With the right tuning tweaks, more than 200 hp can be unlocked from early versions of the Duramax, the 5.9L common-rail Cummins and even certain years of the 6.7L Cummins. As for the ’08-’10 6.4L Power Stroke, in excess of 300 extra ponies can be gained through tuning alone.
Performance Without Sacrifices
As with most diesels produced over the past 25 years, you don’t pay a durability penalty when you add significant power to the equation. In fact, most engine’s horsepower and torque output can be doubled, if not tripled, before serious internal upgrades become necessary. This is why virtually every diesel you come across has been treated to an electronic power-adder of some kind—there is no downside (provided you don’t abuse the extra power).
Modern Transmissions Are Pretty Tough, Too
The transmissions that’ve been mated to the diesels produced over the last 12-15 years (mostly automatics) can handle more torque being thrown their way. Granted, this is the weak link in aggressively tuned trucks (especially Allison-equipped GM’s and Rams fitted with the 68RFE), but transmission control module, or TCM, tuning can keep them from slipping with an extra 200 to 400 lb-ft worth of grunt in the mix. Ford’s 6R140, offered behind the 6.7L Power Stroke from ’11-’19 and shown here, is particularly stout, capable of harnessing 1,200 lb-ft (indefinitely) in stock form.
The introduction of the 5.9L Cummins in Dodge trucks revolutionized the pickup industry and set the stage for (greater) things to come. You can read all about it here.
