What Makes the 7.3L Power Stroke So Great... - Diesel World

And the Aftermarket Parts That Make it Even Better

It possesses the largest displacement in the diesel truck segment, the biggest bore of any V-8 diesel, and the second longest stroke of any V-8 oil-burner ever offered. It’s the 7.3L, the venerable O.G. of the Power Stroke nameplate and the first diesel power plant to reach 500 lb-ft of torque. It’s also the engine that brought full electronic control and an extremely intricate (yet ultimately reliable) HEUI injection system to the diesel industry. Throughout the 7.3L’s production run, it earned a reputation for durability, and even now tens of thousands are still out there on the road, piling up hundreds of thousands of miles on the factory long-block. But that’s not the only thing it’s known for…

The 7.3L is overwhelmingly underpowered and slouchy in stock form, especially by today’s 400-plus horsepower, four-digit torque, and drivability standards. Thankfully, a vibrant aftermarket exists to help bring the 444ci V-8 up to speed. In the pages that follow, we’ll spell out the components that make the original Power Stroke a 500,000-mile contender, and then spotlight all the parts and practices that allow one to make (but also survive) three times the factory horsepower. Your historical guide and performance tutorial for the timeless 7.3L begins here.

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Go back to 1994 for a minute. At that time, when the Navistar-built 7.3L Power Stroke debuted as the replacement for the 7.3L turbo IDI, it sported a crankshaft with larger mains, beefier connecting rods, direct injection, six head bolts per cylinder, and a fully electronic injection system. Though it displaced the same, 444 cubic inches, virtually nothing else was the same

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From the factory, Navistar made sure the 7.3L’s crankshaft would hold up for the long-haul. Made of forged-steel, its main and rod journals, as well as its fillets, were hardened to resist wear. The crankshaft’s 4.18-inch stroke is the second longest ever offered in a V-8 diesel (second only to the 6.7L Power Stroke’s 4.25-inch stroke), which aided the engine’s various instances of class-leading torque figures throughout its nine-year production run.

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Forged-steel was also the material of choice for the connecting rods, at least on ’94.5-’00 model year engines. Somewhere in the ’01 model year (and specifically engine serial number 1425747), powdered metal rods were employed. Then, after switching back to forged rods to use up its remaining inventory from engine serial number 1440713 to 1498318, powdered metal units got the nod until the end of 7.3L production.

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In higher horsepower applications, the forged-steel rods are much more desirable due to their ability to hold up to 600-650-rwhp. By comparison, the general consensus for powdered metal units is that they shouldn’t be pushed harder than 500-rwhp, even with precise engine tuning. Additionally, forged-steel rods are prone to bend rather than break when they fail, while the powdered metal versions typically break (oftentimes damaging the block).

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Just as it shares its injection system with Navistar’s legendary DT466E (and the I530E for that matter), the 7.3L also makes use of six head bolts per cylinder. The half a dozen 12mm diameter fasteners per hole are instrumental in keeping the head gaskets alive for hundreds of thousands of miles at the factory power level. And even when you turn the wick up on the 7.3L, they have no problem keeping the heads glued to the block at 40-psi of boost (if not a little more).

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The 7.3L’s cast-iron cylinder heads are both simple and somewhat complex in design. They feature two overhead valves per cylinder (one intake, one exhaust) but entail integrated oil rails on each inboard side to handle storage for the high-pressure oil side of the HEUI system. Valve actuation is handled by a camshaft that’s conventionally located in the block and that is made of forged-steel.

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Self-adjusting hydraulic lifters mean there is no need to periodically check the valve lash on the 7.3L Power Stroke. Additionally, the lifters are particularly forgiving when slightly longer, aftermarket pushrods sit in place of the stock units.

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Aside from the presence of a catalytic converter, emission control devices were non-existent on the 7.3L. There was no exhaust gas recirculation (EGR) and certainly no exhaust system aftertreatment to speak of. Instead, Tier 1 emission standards were met almost entirely due to the hydraulically actuated electronically controlled unit injection system (HEUI). The other part of the emissions-meeting equation was the use of a turbocharger.

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Unlike the problematic oil-fired injection system that was employed on the 6.0L Power Stroke, the original, Caterpillar-leased HEUI technology and componentry proved very reliable on the 7.3L. With proper care (namely regular oil changes and the use of a quality oil), there is no reason why a 7.3L’s injectors won’t last 200,000 miles before requiring an overhaul. Some even last twice that long. On the electronic side of things, the engine’s IDM and PCM often live long lives, and the vital ICP sensor and IPR valve are easily capable of lasting 150,000 to 200,000 miles at a time.

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While the terms poppet valve and intensifier piston will seem foreign to many diesel lovers and no doubt make the 7.3L’s injectors one of the most complex on the market, in terms of injecting fuel in-cylinder they are fairly straightforward. Early engines employed single-shot units, where a lone shot of fuel was sprayed during the engine’s power stroke. Later, split-shot injectors (first infiltrated in California model engines as AB code injectors starting in 1997) made use of a mechanical pilot event before the primary shot occurred to help quiet the engine down. So despite having two injection events, there was no added wear and tear on the injectors.

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On top of being able to meet stricter emission standards and make more power than the competition, HEUI—the brainchild of Caterpillar—makes it impossible to run the engine out of oil. This is especially helpful in applications where drivers or equipment operators don’t perform regular maintenance or neglect to check the engine’s oil level. Eliminating catastrophic engine failure is a great way to save the company’s bottom line, after all. In the 7.3L Power Stroke’s case, the injectors will fail to fire once the oil level drops below seven quarts.

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When you’re pressurizing engine oil upward of 3,000 psi in the high-pressure circuit, keeping oil temperature in check is vital. The 7.3L’s fluid-to-fluid, externally mounted oil cooler on the driver side of the block does a superb job of it and hardly ever fails. With its optimized location and large internal passageways, it’s a complete 180 from the block-encased and highly restrictive oil cooler present in the 6.0L Power Stroke. About once every 10 to 15 years the 7.3L oil cooler will be due for new O-rings, but the cooler itself rarely ever fails.

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A simple, fixed geometry, journal bearing Garrett turbocharger fed all model years of the 7.3L (the non-wastegated TP38 from ’94.5-’97, the wastegated TP38 in early ’99, and the wastegated GTP38 from ’99.5-‘03). If kept in its map, these turbos can last as long as the engine. Uniquely, there were no external oil lines feeding or returning oil to and from them. Instead, the pedestal was positioned directly above supply and drain ports (and sealed via O-rings) in the block.

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When an engine doesn’t make enough power to hurt itself, it can usually chug along for just about forever. Let’s face it, 215 hp and 425 lb-ft (at its ’94.5 debut) and 275 hp and 525 lb-ft (outgoing rating) isn’t groundbreaking—and it’s also why a bone-stock 7.3L feels like it can’t get out of its own way on 2020 highways. However, by the same token this is why these engines last forever. In fact, if you forgo any form of power adder and properly maintain it, the 7.3L will blow past its B50 life rating of 350,000 miles, and we’ve seen several go half a million miles or more.

From Durable to Powerful:

The Aftermarket Parts That Make The 7.3L Competitive

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Due to a slow micro-processor within the 7.3L PCM (not uncommon in the early days of computers), it’s best to install a chip that piggybacks onto the PCM itself, thereby taking over all control of the PCM. This makes it possible to produce significantly more power than what an OBD-II uploader type programmer can add. The Hydra Chip produced by Power Hungry Performance (shown) is far and away the most common means of custom-tuning a 7.3L Power Stroke.

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Being able to get the most performance possible out of a larger injector without having to upgrade high-pressure oil pumps or run dual HPOP’s is the biggest selling point behind the use of hybrid injectors, and boy do they sell. Popular sizes include 205cc, 238cc, and 250cc hybrids, equipped with anywhere from 30-percent to 80-percent to 100-percent or 200-percent larger nozzles (a 238cc fitted with an 80-percent nozzle is called a 238/80 in 7.3L injector speak). All of the hybrids mentioned above can effectively support 425 to 575-rwhp applications and be run with a healthy factory HPOP.

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Though a single HPOP will suffice in getting the most power out of the aforementioned, “smaller” hybrids, 300/200, 350/200, and 400/400 or larger injectors call for more high-pressure oil volume. To get there, Full Force Diesel Performance‘s dual HPOP pump kit stacks two pumps on top of each other, comes with two injection pressure regulators for ultimate drivability, and can support any size HEUI injector on the planet.

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Electric fuel supply systems and regulated return kits are plentiful in the 7.3L aftermarket, and for good reason. Any time you install larger injectors, a minimum of 65-psi worth of fuel supply pressure needs to be on tap for their use at all times, for both optimum reliability and performance. Fuelab, Aeromotive, Walbro, and even twin OEM Bosch pumps are employed in all-inclusive, tank-to-engine systems. The latter, a twin-pump lift pump system from Driven Diesel is shown here, and is one of the highest quality kits in the industry.

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Dyno sheets all over the country prove that switching to a large frame, T4-flange turbo is one of the best upgrades you can perform on a 7.3L. Irate Diesel Performance has been manufacturing T4 turbo mounting systems for roughly a decade, and helping thousands of 7.3L owners unlock huge power all along the way. Its turbo system facilitates the use of a BorgWarner S300, S400, or GT42-based Garrett. Some of the highest horsepower ’94.5-’03 Fords in the country are running Irate’s T4 turbo mounting system.

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One of the best complements for a T4 turbo mounting system is the box BorgWarner S467.7. Its forged-milled 67.7mm (inducer) compressor wheel flows 90 pounds or air per minute and it employs the common 83/74mm turbine wheel. If you’ve got the fuel for it, this turbo will spool quick (even with the 1.10 A/R exhaust housing), offer solid reliability, and be tow-friendly while supporting 600 to 650-rwhp at the same time.

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For 7.3L’s in the 400 to 600-rwhp range, KC Turbos has made leaps and bounds in drop-in turbo technology over the past few years. The company’s KC300x 66/73 utilizes a 66mm BorgWarner SX-E style compressor wheel, a 73mm SX-E style turbine wheel, and can support 580-rwhp while also being affordably priced at $1,240.

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Increased high-pressure oil volume from a larger HPOP or dual HPOP’s can only be fully utilized if your low-pressure oil pump is up to the task. If it’s not, a higher volume LPOP is necessary. The aftermarket version from Melling is a popular upgrade, but the high volume LPOP from DieselSite is the most efficient pump in the industry, employing custom cut gears that increase flow as well as pressure, while also reducing cavitation.

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On engines that see more than 40 psi of boost, ARP2000 head studs are more than enough fastener for most 7.3L gurus’ head-to-block clamping needs. And many owners that push the factory, forged-rod bottom end to the limit even install them one at a time rather than pull the heads. In our experience, going beyond 75 psi of boost warrants fire-rings to keep head gaskets alive.

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Connecting rod upgrades abound in the 7.3L aftermarket, and should be considered in any engine build where the end goal exceeds 600 to 650-rwhp. Crower, Carrillo, Hypermax, Brian Crower, and Manley (shown) all offer aftermarket rods designed to handle big horsepower. Crower’s billet-steel rods, Carrillo’s H-beam units, and Hypermax’s forged versions have all been proven for years. Also proven but geared more toward budget engine builds are the Pro I-beam rods from Manley ($2,381.16 through Riffraff Diesel) and the ProHD series rods produced at Brian Crower ($2,175). Both of the latter options come standard with ARP2000 rod bolts.

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High rpm and excessive boost can lead to valve float and valve creep, especially with the factory valve springs still in the heads. Providing just 71 to 79 lbs of seat pressure, they’re one of the first things you need to address when making horsepower with a 7.3L. For trucks making 350 to 550-rwhp, the tried and true Comp Cams 910 valve springs (properly shimmed to yield the target seat pressure) are the most affordable and effective means of addressing the weak factory springs. For power levels approaching 600-rwhp to venturing well beyond it, Irate Diesel Performance’s 150-lb seat pressure competition valve springs are a hot commodity.

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When you double the power of a 7.3L, the flimsy stock pushrods could bend or deflect at any time. For years, Smith Brothers pushrods have been the pushrod of choice in 7.3L builds. Their 4130 chromoly-steel construction makes them much stronger than the factory units, and a Stage 2 option increases their wall thickness from 0.065-inches to 0.120-inches for utmost peace of mind when making 600-rwhp or more.

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While respectable power can be made without deviating from the 7.3L’s factory camshaft, there are definitely gains to be had with a simple drop-in unit. Case in point, the Stage 2 billet cam from Colt Cams and the Stage 1 version from Gearhead Automotive Performance are direct replacements (i.e. no valve pockets required in the pistons) and feature profiles that produce quicker spool up, lower EGT, and all-around better drivability. They also prevent reversion from occurring with high drive pressure in the mix.

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Any time the 7.3L’s cylinder heads are ported and matched with the right cam, serious horsepower gains can be had. Just ask Brian Jelich of Jelibuilt Performance and Scott Morris of Morris Motorsports. Each of them has campaigned a set of heads done up by Crutchfield Machine and matched with a more aggressive cam. The result? Jelich’s single turbo’d Super Duty picked up 3 mph in the eighth-mile (which correlates to 100 hp) after combining a Stage 2 Gearhead cam with his Crutchfield heads. As for Morris, his compound turbo’d engine sports a custom-spec cam from Comp Cams in conjunction with Crutchfield ported and fire-ringed heads, and is believed to make an insane (for a 7.3L) 950-rwhp on fuel.

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At extreme power levels, main cap walk is a real problem on the 7.3L. To rule out the issue, Irate Diesel Performance offers a competition-caliber girdle that ties all the mains in with each other (shown), and it also comes with ARP main studs and the tab that’s required to make the factory oil pickup tube work. To rule out main cap movement altogether, Hypermax offers a complete bed plate. Its installation requires that modifications be made to the factory oil pan, but it’s been proven in applications making north of 1,500 hp.

The Ultimate 7.3L?

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Reserved for competition-only use, many 7.3L die-hards have turned to mechanical injection to get the 444ci V-8 into the 2,000hp realm. Most recently, the guys at Unlimited Diesel Performance have campaigned a P-pumped 7.3L puller in the Limited Pro Stock field (and also made 2,180 hp on the engine dyno while testing with a larger turbo). The Jumping Jack Flash crew has also made a splash in the Pro Stock class with their Hypermax-built 7.3L. Over at the drag strip, Matt Kubik has sent his ’98 Mustang through the quarter-mile in 7.60 seconds at 192 mph (a Power Stroke record) thanks to a Hypermax engine with select Scheid Diesel parts.

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Elevated rpm and high engine load can force the cam gear to walk off of the shaft itself. For peace of mind, TIG welding the cam gear to the shaft (usually in three or four places) is a highly common practice. Another insurance item usually performed during an engine build is welding the piston oil squirters in place.

SOURCES

ARP
800.826.3045
arpdiesel.com

Brian Crower
619.749.9018
briancrower.com

Carrillo
949.567.9000
cp-carrillo.com

Colt Cams
604.856.3571
coltcams.com

Crutchfield Machine
336.451.0108

DieselSite
888.414.3457
dieselsite.com

Full Force Diesel
615.962.8291
fullforcediesel.com

Hypermax Engineering
847.428.5655
gohypermax.com

Irate Diesel Performance
503.435.9599
iratediesel.com

KC Turbos
480.688.7160
kcturbos.com

Manley Performance Products
732.905.3366
manleyperformance.com

Melling
517.787.8172
melling.com

Power Hungry Performance
678.890.1110
gopowerhungry.com

Riffraff Diesel Performance
541.879.1052
riffraffdiesel.com

Scheid Diesel
800.669.1593
scheiddiesel.com

Unlimited Diesel Performance
740.569.1319
unlimiteddiesel.com