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The Story Of A 600 HP, Stock Bottom End 7.3L, Part 1

Surviving 10 Years At High-Horsepower

Picture the way diesel performance was 10 years ago. At the time, tuned 6.4L Power Strokes—capable of dynoing 570 to 590 hp and collecting 12-second timeslips at the drag strip—ruled the roost as far as average, daily-driven, do-everything late-model trucks were concerned. Of course, the Duramax and common-rail Cummins offerings weren’t far behind, with 500hp tune-only trucks rampant throughout the population. For any 7.3L Power Stroke enthusiast, where 500 hp was a big deal (and took some extensive work to achieve), it was plain to see they were going to be left behind. In an effort to remain relevant in the world of 500 and 600hp daily drivers, yours truly embarked on a series of upgrades to help bring his ’97 F-350 up to speed.

Because a Cummins swap wasn’t on the table, it was either A. take a chance on the factory 7.3L holding up to big power, or B. fork over the cash to start fresh with a built 7.3L. Thanks to a limited budget at the time, I elected to go with option A. Although many 7.3L owners had stacked a 600-rwhp combination on top of the factory rotating assembly and managed to keep their engines alive, there were plenty of horror stories out there, too. Despite not knowing whether my own 175,000-mile Power Stroke would live or not, I decided to roll the dice anyway and see if it could. Ten years later, the 225,000-mile 7.3L Power Stroke in this OBS Ford is still ticking.

This series will highlight the parts that got the truck to the 600-rwhp mark, as well as the sensible driving techniques that were used to keep the stock bottom end alive for so long.

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“Humble beginnings” would be an understatement, as my bone-stock OBS 7.3L Power Stroke could barely get out of its own way when I picked it up 16 years ago. However, the 87,000-mile crew cab 4×4 F-350 was clean, well-maintained and, as I would find out, had never had a chip attached to its PCM (powertrain control module). It’s possible that the easy initial break-in period for the 7.3L (with its 225 hp rating, at the crank) helped ready the 444 ci V-8 for the added power it would see in the years that followed.
As the owner of my ’97 F-350 since 2006, I have to admit that my horsepower journey with the truck didn’t begin 10 years ago. In fact, prior to chasing 600 hp at the wheels I’d already pushed the truck from 159-rwhp (stock) to 502 hp on the rollers—and midway through that process the heads were pulled, the block and head surfaces were checked, and fresh gaskets and ARP studs were added. The ARP heads studs (PN 250-4201) were torqued to 125 ft-lbs and have been in place since 2011.
With the heads off the block I was able to see that the factory cross-hatching was still present in each cylinder—reason enough to push forward with the goal (at that time) of pursuing 500 hp. On this visit, the block’s deck surface checked out within spec (no more than 0.003-inches of warpage within a 6-inch radius, or no more than 0.006-inches overall). The heads checked out great, too, with less than 0.001-inches of difference in any one area (Ford suggests that warpage should not exceed 0.001-inches within a 2-inch radius, or no more than 0.004-inches overall).
Surprisingly, the valvesprings weren’t upgraded when the heads were off for the head stud job. Instead, they were swapped in, one at a time, more than a year later. The factory 7.3L valve springs are one of two key areas in the valvetrain that must be upgraded before elevated boost and higher rpm is on the table. Stock, they provide a closed seat pressure of 71 to 79 lbs, which makes them prone to reversion (when the exhaust valves open during the intake stroke due to excessive drive pressure) as well as valve float at anything over 3,300 rpm.
Our aftermarket valve spring choice was the big-block GM-derived “910” valve springs from Comp Cams. Cheap and effective, they cost less than $100 and when combined with 0.030-inch case-hardened steel shims they increased seat pressure at their installed height to approximately 113 lbs. As mentioned, each Comp Cams spring was installed one at a time. It was performed by using the valve spring compressor tool shown and manually rolling the engine over to bring each piston to TDC before installing them. The glow plug bores were used to check for TDC (via probe) and the glow plugs were replaced while the valve covers were off.
Another notorious weak point within the 7.3L Power Stroke’s valvetrain are its pushrods. They tend to flex at high rpm and it’s wise insurance to address them early on in your horsepower journey. I replaced the stockers with a set of 4130 chromoly units with a 0.095-inch wall thickness and 8620 steel pressed-in ball ends. They came from Hamilton Cams.
After running a set of 160cc, stock nozzle injectors (which supported 350 hp), I stepped up to 238cc hybrid injectors (which supported 500 hp) before switching over to 350cc hybrids from Unlimited Diesel Performance. Essentially the second largest off-the-shelf injector you can buy, they can support well north of 600 hp provided you’ve got enough air (and high-pressure oil) to go along with it. Internally, they’ve been treated to what are referred to as fuel-side modifications, which entails the addition of fuel plates within the injector bodies. On the high-pressure oil side, a shorter intensifier piston is employed for increased stroke.
Equipped with 200-percent over nozzles, the 350cc hybrids are coined 350/200’s for short. By flowing 200-percent over stock, they provide for an injection rate that is exceptionally fast. This means lots of fuel can be delivered within a very limited window of time—which is ideal given the 7.3L’s small window for making power. Like the factory nozzles, they retain a 7-hole design. However, each orifice measures 0.0120-inches vs. 0.0060-inches stock. In aftermarket injector lingo, this means our 350/200’s are equipped with 7×12 nozzles.
So what makes a hybrid injector a hybrid? In the world of 7.3L’s, it means taking an A-code injector, which is native to the 7.3L Power Stroke and Navistar T444E engines, and outfitting it with the plunger and barrel assembly out of BD-code injector, which comes from the Navistar I530E inline-six engine. In going from a stock 6.0mm od plunger to a 7.1mm od plunger, this effectively increases the bore of the injector. In addition, the factory intensifier piston (the oil-side amplifier that acts on the plunger on the fuel side) is retained. By retaining the stock intensifier piston in standard hybrid injectors, less oil is required to actuate the injector than would be necessary in a BD-code injector. As was previously mentioned, the intensifier pistons in our 350/200’s have been machined down to increase stroke.
Looking at the data in this flow sheet for a set of similar 400/200 hybrid injectors, you can see that the 200-percent nozzles enable a boat load of fuel to be injected with very little injector pulse width (pulse width being the duration of the electrical signal sent to the injector solenoid telling it to fire). With 3 milliseconds (M/S) of pulse width (all we were going to have commanded via tuning to keep things safe), 3,000-psi of injection control pressure (ICP) on tap, and 65-psi worth of fuel pressure feeding the injectors, the hybrids can flow 317cc’s of fuel.
It’s a very far cry from the OBS Ford’s factory, cam-driven mechanical diaphragm lift pump in the lifter valley, but it’s what 600 hp calls for. To ensure the injectors see 65-psi of supply pressure at all times along with more than sufficient volume, Irate Diesel Performance’s competition fuel system got the call. Highlights include a Fuelab lift pump, ½-inch diameter Parker supply hose rated at 300-psi, 3/8-inch Parker return hose, a wire harness, all necessary fittings, and Baldwin filters (fuel and water separator).
With a wet, DC brushless motor design (i.e. no dynamic shaft seals or motor brushes that wear out or corrode) and a “forever fixed” lifetime warranty, the Prodigy 41401 lift pump from Fuelab is arguably the best competition-ready fuel pump in the 7.3L aftermarket. To keep the pump from humming along at full song all the time, we set our Fuelab unit up to operate at continuous reduced speed, which still moves 110-gph at 65-psi.
Prior to switching over the Irate’s competition fuel system, I was using a homemade fuel system that was a bit overkill, but worked. It revolved around the use of an Aeromotive A1000 fuel pump, used 5/8-inch supply hose to feed the A1000 before Y-ing into 3/8-inch lines prior to entering the heads. It also featured a 3/8-inch return line that replaced the tiny, 5/16-inch od factory line. Our reason for upgrading to Irate’s competition system was twofold: 1. We didn’t know how long the A1000 would survive in street use (and without the optional speed controller) and 2. We were beginning to see quite a bit of corrosion on our 5-year-old homebuilt system.
As part of Irate Diesel Performance’s competition fuel system you also get a regulated return setup. Regulated return systems ensure that consistent fuel pressure is always being supplied for the injectors to use. Irate’s kit uses a Fuelab adjustable pressure regulator and comes with 304 stainless steel lines. After the Fuelab pump sends fuel supply to the rear of both cylinder heads, fuel returns out the front of the heads to the regulator, then back to the tank.
Compared to a factory HPOP, the SRP1.1 was still an axial piston, fixed displacement pump, but it was treated to larger pistons in order to increase its output flow. The piston on the left measures 0.500-inches in diameter (SRP1.1) while the unit on the right checks in at 0.436-inches-inches (stock). This upsizing in the pistons, which called for a reengineered brass cylinder block (with thicker walls) to house them, culminated in an HPOP that provided a 32-percent increase in flow over a factory 17-degree HPOP and 45-percent more flow than what a 15-degree HPOP provided.
The SRP1.1 high-pressure oil pump from the late Stealth Industries is no longer in production, but when I first installed it back in 2013 it was one of the best single HPOP options for supporting larger hybrid injectors. This HPOP (and particularly the pump that preceded the 1.1 version) gets a bad rap for self-destructing, but in our case it’s lasted 50,000 trouble-free miles—not to mention the fact that it’s never failed to hold 2,900 to 3,200 psi worth of ICP.
Part of the corrosion that prompted us to take a closer look at the fuel supply system (and the truck as a whole) started with a rusting front factory fuel tank. So before I installed the new Irate system I picked up a Dorman direct replacement tank from Summit Racing, along with new tank straps and a new Ford sending unit. The last order of business for the tank was the install of a sump from Bean Machine, the company’s one bolt, one hole, USA-made solution for the 1/8 tank issues associated with pickup tubes.
Completing the higher flow equation, the SRP1.1 featured larger output ports (0.360-inches vs. 0.210-inches stock), and also came with #8 SAE ORB fittings rather than #6 SAE ORB fittings in an effort to prevent the threads from stripping or blowing out. And instead of increasing the swash plate angle to give the pistons more stroke, Stealth left the angle at 17 degrees to ensure that over-stroking (and the side-loading it can cause) wasn’t ever a concern.
It’s important to note here that I had already previously scrapped the factory rear tank due to rust back in 2013, and while this cut the truck down to a sole, 19-gallon fuel tank, a 33-gallon Transfer Flow fuelbox exists in the bed for extra capacity. At the time the rear tank was deleted from the equation I was looking for ways to ditch weight (to help drop E.T. at the drag strip), and the tank and its corresponding skid plate saved more than 100 pounds. However, in order for the fuel gauge on the dash to continue working the factory selector valve had to remain plugged in and in place along the frame rail.
To accommodate the SRP1.1 HPOP, I converted to the quick-connect style high-pressure oil lines used in Super Duty applications (the factory lines are threaded on the OBS engine). You can see both the passenger and driver side lines installed here. Through Ford, these OEM high-pressure oil lines can run you more than $320, but sourced through Riffraff Diesel they can be had for less than $200.
No 600hp 7.3L recipe is possible without custom PCM tuning, namely for dialing in the injection system—which in my case would ensure the 350/200 hybrids and SRP1.1 HPOP worked in perfect harmony with one another. My calibration needs were fulfilled by Gearhead Sales and the custom tunes are available on the fly thanks to a Hydra chip from Power Hungry Performance.
Through the use of both Power Hungry Performance Minotaur software and Sniper Delta Force software, Gearhead builds some of the most refined, linear throttle tunes on the market. Its tunes are also created with optimum engine longevity in mind (i.e. they’ll keep your rods inside your block), and that applies to its All Out calibrations as well. In fact, in tune number 6 (shown)—the file that’s sent the truck through the eighth-mile the quickest and made the most power on the dyno—only 14 degrees of timing advance is on the table. Better yet, that peak injection timing isn’t even available until 3,200 rpm. This is one reason why the rods are still in the block.
Although the Hydra will hold as many as 15 custom calibrations at a time, I’m only utilizing seven positions. At the present time, the tunes include Heavy Tow, High Idle, Stealth Mode, Heavy Tow 2, Street Fury, All Out, and a second All Out file. The second tow file was specifically created for towing my toy hauler (the maximum weight the truck gets hooked to) and the All Out files are the 600hp-capable tunes.
The best thing about running a large hybrid injector with a 200-percent nozzle is that your tuner can always dial them back. In my tow tunes, I can still tote a 10,000-pound trailer without worry that EGT will get out of hand. This is an impressive feat, and one that Gearhead pulls off all the time for stock bottom end 7.3L owners. In my case, it’s exceptional when you consider I’m running one of the largest off-the-shelf fuel injectors you can buy. This tune has undoubtedly contributed to the bone-stock short block’s longevity.
Programming the Hydra chip calls for a Windows-based computer and Power Hungry Performance’s Hydra Flash program, which is free to download. When tweaking or changing positions on the Hydra, I move emailed files into a dedicated desktop folder before programming them onto the chip itself. The reprogramming process is very straightforward and is accomplished in seconds, due to in part to a 7.3L tuning calibration only consuming roughly 257 KB.
Like any 7.3L chip that piggy backs onto the PCM, the Hydra chip is no different. But what does make the Hydra unique is its ability to be reprogrammed without removing the chip from the PCM’s circuit board. This USB extension cable, a $25 option, makes it possible. Trust us, in a 600hp build that spans 10 years there are inevitably going to be a few tweaks that are required to dial everything in.

SOURCES

ARP
800.826.3045
arpdiesel.com

Bean Machine
844.237.7467
bdpshop.com

Gearhead Sales
979.703.7338
ghtuning.com

Irate Diesel Performance
503.435.9599
iratediesel.com

Power Hungry Performance
678.890.1110
powerhungryperformance.com

Riffraff Diesel Performance
541.879.1052
riffraffdiesel.com

Summit Racing
800.230.3030
summitracing.com

Transfer Flow
833.375.3132
transferflow.com

Unlimited Diesel Performance
740.569.1319
unlimiteddiesel.com

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