Remaining Relevant: How To Make Your Older Diesel Keep Pace With Detroit’s Latest 1,000 LB-FT Monsters

• November 12, 2022
• Story By
  Mike McGlothlin

Today’s diesel pickups are downright serious. They’re so powerful that the lowest factory horsepower rating at the present time is 420 hp (6.7L Cummins) and the weakest torque output is 910 lb-ft (L5P Duramax). To anyone even remotely familiar with diesels, it’s plain to see that with numbers like these the oil-burners of yesteryear are being left in the dust. But how exactly do you get your old workhorse to keep pace with Ford’s 450hp, 1,050 lb-ft 6.7L Power Stroke, the 1,075 lb-ft 6.7L Cummins in late-model Rams or GM’s 445hp, 910 lb-ft L5P Duramax? Short answer: you add the right parts in the right places.

With most ’20 or newer diesel trucks applying roughly 400 to 420 hp to the pavement right off the showroom floor, the few modifications that you need to make in order to keep up must be geared toward not only increased horsepower and torque, but reliable horsepower and torque. After all, it’s pretty hard to trailer-race with a brand-new diesel when you’re on the verge of melting a piston. Luckily, there are highly-proven parts combinations to help you and your old friend compete with modern diesels—and we’re supplying you with a blueprint of everything you’ll need below.

Ford 7.3L Power Stroke (‘94.5-‘03)

The only real way to get substantial performance gains from a 7.3L is through the use of bigger injectors, combined with matching powertrain control module (PCM) tuning. After that, you want to add more air to the equation which, in addition to keeping exhaust gas temperature (EGT) in check, will facilitate further horsepower gains. By more air we mean either a drop-in turbo upgrade or (even better but more expensive) a complete T4 turbo mounting system. The turbo (or complete turbo system) you choose should utilize a 63mm to 66mm compressor wheel (60mm is stock). Entry-level injectors, refined PCM tuning and a higher-flowing turbocharger can easily boost a 7.3L Power Stroke to 400rwhp and 800 lb-ft.

Ford 6.0L Power Stroke ('03-'07)

A higher pressure HEUI injection system makes the 6.0L Power Stroke more potent than the 7.3L with tuning alone. In fact, well-crafted PCM tuning can boost a 6.0L-powered Power Stroke to 400rwhp. However, an upsized, drop-in variable geometry turbocharger can help ensure high EGT and intake air temperature (IAT) is never a worry—and if you combine a higher-flowing VGT with a set of entry-level performance injector nozzles you could easily be sitting at 450rwhp or more, along with 800 lb-ft of torque. That, and you’ll have an engine that runs as cool as stock. Of course, head bolt issues may need to be addressed with these kinds of power gains. Modify at your own risk or work a set of head studs into your budget.

Ford 6.4L Power Stroke ('08-'10)

This one is easy. With its Siemens high-pressure common-rail injection system and factory compound turbo arrangement the 6.4L Power Stroke can turn out nearly 600rwhp with an aggressive file uploaded to the PCM. Those Camaro-killing tunes are fun and all, but a well-refined 450rwhp tune will allow the OEM 52mm, 65mm turbo combination to keep EGT low. In addition, at 450rwhp the 5R110W TorqShift transmission can be kept alive indefinitely and 900 lb-ft of torque (or more) will be making it to the wheels.

Dodge Ram 5.9L Cummins 12-Valve ('94-'98)

Although they left the factory configured to produce a measly 160 to 215 hp at the crank, the P-pumped 5.9L Cummins can be mechanically tweaked to produce double that amount relatively easily. However, beyond doubling its horsepower you’ll have to get a little more hands-on with the P7100. Your mod list should include 3,000 rpm governor springs, a properly set up air fuel control (AFC) and likely no fuel plate, which with a 215hp pump can get you into the 350 to 375rwhp range. Add a 62mm or 63mm turbo—in the form of a BorgWarner S300 or upgraded Holset HX35W—and you’re knocking on the door of 400rwhp and 800 lb-ft while running cool and capable of towing anything.

Dodge Ram 5.9L Cummins 24-Valve (’98.5-‘02)

The 5.9L ISB requires a mandatory injector upgrade to break the 400rwhp barrier, but when coupled with a turbo upsizing 400 to 450rwhp is easily obtainable. The trick is not to overdo it on injector. A 100hp set of injectors (sometimes listed as having “7x0.009” nozzles) is an entry-level type upgrade that won’t build too much heat towing, and the heat is does create can be quelled with a higher-flowing turbocharger (i.e. more air). Like the 12-valve Cummins, a 62 or 63mm S300 or a hybrid HX35W are great turbo options for 400 to 450rwhp (and 900 lb-ft). Good tuning is also part of the 450hp requirement. And last but not least, for reliability purposes work an electric, chassis-mounted lift pump into your budget to keep the VP44 injection pump happy.

Dodge Ram 5.9L Cummins Common-Rail ('03-'07)

On tuning alone, an ’03-’07 Dodge Ram equipped with the common-rail 5.9L Cummins can approach 490 to 500rwhp. Things get extremely hot at that point (think EGT, again), but dialing things back to 400rwhp via tuning makes for much more manageable heat. A slight turbo upgrade, again the tried and true 62 or 63mm S300 should get the call, will put any EGT worries to rest and make for an all-around tow-rig that’s more than capable of getting out of its own way.

Chevy/GMC 6.6L Duramax ('01-'16)

From the LB7 to the LML (2001-2016), Duramax-powered Chevrolet Silverado and GMC Sierra HDs can be awakened in a major way with nothing more than tuning. Thanks to its use of high-pressure common-rail injection the Duramax platform can easily be calibrated to produce 400 to 450 hp at the wheels. Better yet, at these power levels the factory Allison 1000 (if equipped) can be kept out of the danger zone. With on-the-fly tuning available, 500 or more ponies can be squeezed out of every Duramax produced to date. Just save the big boy file for when you’re unhooked from the trailer—and until after you’ve beefed up the transmission.

A Word On Transmissions

In general, the newer the truck the better chance its transmission has of surviving added horsepower and torque. While the ’94-’07 Cummins options listed above can be made to run reliably and cool at 400 to 450rwhp, the four-speed automatic transmissions many of them came with won’t hold up without a few upgrades. As for the 7.3L Fords, the E4OD and 4R100 automatics can easily be killed with 400rwhp (and 800 lb-ft) and regular abuse in the mix. GM trucks sporting the Allison 1000 have the best chance of surviving power gains in stock form, but the five-speed version used in ’01-’05 model HD’s is easily the weakest and won’t live forever at 450rwhp.