The Story Of A 600 HP, Stock Bottom End 7.3L, Part 3

Dyno Numbers, Drag Racing, And Towing With A 25-Year-Old Ford

Ten years into our 600hp stock bottom end experiment, the 225,000-mile 7.3L Power Stroke in our ’97 F-350 keeps on ticking. To be sure, its horsepower recipe is extensive—and includes 350/200 hybrid injectors, an S400 turbo, and a billet internal transmission—but the factory rotating assembly is 100-percent as it was when it first left the assembly line back in the late ‘90s. The heads are untouched for the most part, too, their only upgrades being ARP head studs and stiffer valve springs.

Over the course of the last decade the truck has been subjected to dozens of dyno pulls and countless more passes at the drag strip—and it’s all been carefully documented. But while the immediate aftermath of the build meant the truck was often used for play, it continued to be a daily driver. In recent years, and primarily because the engine hasn’t let go or shown any signs of giving up, the OBS Ford has become a tow-rig above all else. You can usually find it hooked to a 10,000-pound toy hauler in the spring, summer, and early fall.

For the third and final installment of this series, we’re taking a look at the truck’s finest hour on the dyno and at the drag strip. Then we’ll highlight the upgrades we’ve made to improve its towing manners and theorize why we think the 7.3L has lasted so long at this power level. Whether the O.G. Power Stroke continues humming along for another 10 years or sends a rod through the block tomorrow is anyone’s guess, but given the trouble-free track-record it’s accumulated so far, we’re definitely not afraid to give it the chance.

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You’re looking at the biggest dyno numbers we’ve squeaked out of our ’97 F-350: 589 hp and 1,123 lb-ft of torque. While we believe 600 hp or more could be gleaned out of our setup, the tuning masterminds at Gearhead Sales delivered on their ability to keep our stock bottom end alive. Peak timing checks in at just 14 degrees in our most aggressive file, and the timing advancement it brings to the table doesn’t peak until after 3,000 rpm—perfect for limiting the kind of low-rpm torque that can bend rods or crack pistons.

The truck’s 589hp number was made on a DynoJet 224xLC, a twin roller, two-wheel drive eddy current dyno. On top of the dyno’s ability to load the truck, the pulls were made in Overdrive. Chassis dyno testing in Overdrive is common practice to ensure maximum boost is made on the rollers, but it’s also a good way to limit tire slip on higher horsepower applications.

Trips to the drag strip often entail dropping weight by ditching simple items like the tailgate, spare tire, rubber bed liner, tools, and also by showing up on a quarter tank of fuel. Doing this can get the crew cab long bed Ford’s weight down under 7,000 pounds on race day. And for a little more footprint, we always drop air pressure down to 25-30 psi in each tire before hitting the track.

Although the OBS has run 8.0’s in the eighth-mile on countless occasions, this is the quickest pass it’s ever made: an 8.001 at 84.88 mph. It’s an E.T. and trap speed that matches our dyno numbers. Launching in 4-Hi with 8 to 10 psi worth of boost on tap always seems to lead to consistent 1.77 to 1.79-second 60-foots, too, which has allowed us to get the jump on a boatload of street cars. Some notable kills from our days at drag strip include a Roush 427R Mustang, a fourth-generation Z28 Camaro with bolt-ons, and several Shelby GT500 Mustangs that couldn’t find traction.

According to the popular online Wallace Racing calculators, our eighth-mile E.T. and trap speed converts to 12.70s and 105 mph in the quarter-mile. Though we’ve raced the truck on quarter-mile tracks, it wasn’t at the same sub-7,000-pound race weight we benefitted from when we earned our 8.0 timeslips at our local track. With an extra 500 pounds onboard thanks to being full of fuel, fitted with the tailgate, spare tire, and hauling tools, bottom 13’s were all we could squeeze out of the old Ford in the ‘1320.

High 1.7-second 60-foots are the norm for the truck and these short gusset traction bars from One Up Offroad have a lot to do with it. Not only do they keep the rear axle from wrapping (a completely untouched, save for a Mag-Hytec diff cover, 10.25-inch Sterling), they’ve likely saved us from damaging the transfer case during all the boosted, four-wheel drive launches we’ve performed. On OBS Fords, the BorgWarner 1356 is only mounted to the transmission, which makes it very susceptible to damage if axle wrap is violent enough.

By far, the AeroForce Technology Interceptor scan gauge that sits in the bottom of our gauge pod is one of the best investments we’ve made. Not only can this all-in-one digital gauge read and clear DTC’s, but it can also display injection control pressure (ICP) and injection pressure regulator (IPR) duty cycle. As a bonus, it can even perform an injector buzz test and a cylinder contribution test for troubleshooting.

An add-on, 100-psi boost pressure sensor allows us to keep tabs on boost from the Interceptor scan gauge (Analog 1 shown). At wide-open throttle in Overdrive, the S468 produces 46-48 psi of boost, but in cold ambient temperatures it has touched 50-psi in the past. Despite being a big single S400, the turbo’s utilization of a .90 A/R exhaust housing and the 2,100-rpm stall torque converter makes for a very drivable recipe on the street.

Analog gauges along the A-pillar are a carryover item from the truck’s early days of receiving modifications, but they only seem to complement the look of the old-school Ford. Believe it or not, the truck could easily peg the previous 1,600-degree pyrometer when drag racing, which prompted the install of this 2,000-degree gauge when we upgraded to Auto Meter Phantom series units back in 2019. The needle position on the transmission temperature gauge shown is as high as it’s registered with the TorqShift-intended Mishimoto transmission cooler in place (150 degrees), even on 95-degree days.

Improving the towing experience is a set of rear air springs from Air Lift. The company’s Load Lifter 5000 Ultimate kit provides up to 5,000 pounds of load-leveling capability. And while they aren’t mandatory for the truck’s normal workload, the air springs do provide a noticeable improvement in stability when towing. Of course, they’ll also come in handy if we ever hook on to a trailer with considerable tongue weight.

Once it’d proven itself reliable, our trust in the truck began to grow. Now, we hook on to a 10,000-pound toy hauler without a second thought. In fact, many of the truck’s summer miles are accumulated with this 31-foot Jayco behind it. As mentioned, the higher stall torque converter and tighter available exhaust housing on the S468 make towing with 350/200 hybrid injectors a smoother process than you might think.

One “old-man” addition came in the form of mirror extensions. If you know anything about OBS Fords, you know the factory mirrors are worthless with a wide, enclosed-type trailer behind you. These extensions came from Complete Performance, the OBS gurus out of Jasper, Texas, and can move each mirror outward an additional 5.5 inches. Without them we would probably still be trying to back into our campsite…

Along with the air springs, an investment was made in improving the truck’s ride quality back in 2019. New leaf springs (front and rear), hangers, shackles, and U-bolts were installed, along with Grade 8 hardware throughout. Not only does the truck ride a bit plusher now, but it’s safer and even sits a tad higher thanks to the fresh shackle bushings.

After realizing the truck could be a dependable, predictable tow-rig, further investments were made—and a new Class V receiver hitch from Draw-Tite was one of them. Made from 5/16-inch steel (as well as being taller and wider than the factory-installed hitch), Draw-Tite’s Class V Ultra Frame, 2-inch receiver hitch was definitely an upgrade. Its maximum weight carrying capacity is 10,000 pounds, and 12,000 pounds with a weight-distributing hitch.

We won’t lie, the towing experience can yield 1,200 degrees F on the pyrometer fairly easily on slight grades, but that’s to be expected in dead-of-summer travel with excessive ambient temps. It’s also to be expected when towing with the second largest off-the-shelf 7.3L injectors you can buy. But remember, the 7.3L’s EGT danger zone is 1,250 to 1,300 degrees sustained. Most of the time, towing produces what you see here: EGT in the 1,000 to 1,100-degree range.

The current odometer reading doesn’t represent some crazy, high-mile 7.3L Power Stroke, but for the last 50,000 of these miles, the truck has been equipped with the same horsepower recipe that made 589 hp and 1,123 lb-ft on the dyno. What’s more is that the truck has essentially been a test mule for bigger injectors, turbochargers, and HPOP’s—and has been making 350-rwhp or better—since the 125,000-mile mark. That’s 100,000 miles making at least twice the power it left the factory with.

Perhaps the biggest key to our high-horsepower, stock bottom end 7.3L’s ability to tow effectively lies in what’s going on here. In position 4 on our Power Hungry Performance Hydra chip, Gearhead Sales wrote us a file designed specifically for towing. File number 4 entails a later converter lockup point in third gear, which ensures more rpm (and boost) is on tap before the coupling event with engine occurs. If we had to guess, this heavy tow file produces roughly 350 to 400 hp at the wheels.

Based on how long it’s lasted at higher horsepower, our stock bottom end 7.3L serves as a great testament to the kind of spot-on tuning Gearhead Sales offers. Our engine has been in their capable hands for more than 12 years at this point and—knock on wood—we haven’t bent a rod, cracked or melted a piston, or dropped a valve seat to date. Better yet, the truck still returns respectable fuel economy, offers a linear throttle pedal feel for great drivability, and the engine idles as tamely as a 7.3L with a set of mild, single-shot injectors in it.

With the original goal being to keep pace with mildly modified Duramax’s, common-rail Rams and stay a step ahead of tuned 6.4L Power Strokes. Nowadays pretty much every 6.4L Ford has disappeared, but the old 7.3L keeps doing its thing. It makes one wonder if it’ll outlive the 6.7L Power Strokes, too. Only time will tell.

Despite what we were told might happen with the SRP1.1 high-pressure oil pump, it has lasted 50,000 trouble-free miles so far. And even though it’s on the edge of its capabilities, it’s always maintained at least 2,900 psi worth of ICP with the 350/200’s in the mix. For a stock replacement pump (what SRP stands for), the SRP1.1 has more than lived up to our expectations since installing it way back in 2013.

Because we know we’re playing with fire with a 600hp stock bottom end 7.3L, plans for a built engine are in the works. After securing a low-rust, core long block, we started rounding up the parts we’ll use in the build. One aftermarket addition is shown here: Manley Performance connecting rods. We’ve seen these I-beam rods, which are made of 4340 forgings, in several 800hp trucks and would fully trust them to handle our future power goals.

One key to the stock bottom end surviving the 600hp onslaught can’t be overlooked, and that’s our sensible driving style. Although we hold nothing back at the drag strip or when strapped to the rollers, the truck spends most of its time in the aforementioned 350 to 400hp tow tune. To sum it up, we don’t abuse the engine—and we respect its power potential. Sure some spirited street driving takes place in the 600hp setting, but it’s not every day.

What do our future horsepower plans look like? Given the truck’s race weight, our goal of running 7.70s in the eighth will require 650 hp at the wheels. To get there and keep the engine reliable, we’ll go with the aforementioned Manley rods, a girdle with ARP main studs, thermal and dry-film coated pistons, a block with its water jackets half-filled, and an upgraded cam. The same 350/200 hybrid injectors will be along for the ride (as well as the fuel supply system), but dual high-pressure oil pumps will enter the fray, along with a Melling lowpressure oil pump and a welded cam gear and oil squirters. With any luck, we’ll make it a point to compete in the 7.70 Index class at a few select ODSS races.

SOURCES

AeroForce Technology
aeroforcetech.com

Air Lift Company
800.248.0892
airliftcompany.com

ARP
800.826.3045
arpdiesel.com

Bean Machine
844.237.7467
bdpshop.com

Complete Performance
409.383.6004
cpaddict.com

Draw-Tite
800.632.3290
draw-tite.com

Driven Diesel
623.582.4404
strictlydiesel.com

Gearhead Sales
979.703.7338
ghtuning.com

John Wood Automotive
jwtt.com

Power Hungry Performance
678.890.1110
powerhungryperformance.com

Unlimited Diesel Performance
740.569.1319
unlimiteddiesel.com

FORD F-350

YEAR: 1997
ODOMETER: 225,172 miles
MILES AT 600 HP: 50,000 miles
MILES AT 500+ HP: 70,000 miles
MILES AT 350+ HP: 100,000 miles
BLOCK: Factory forged-steel crankshaft, forged-steel rods, forgedsteel camshaft, and cast-aluminum pistons
HEADS: Factory 2-valve cast-iron with ARP head studs Valvetrain Mods: Comp Cams 910 valve springs, Hamilton Cams chromoly pushrods
FUEL INJECTORS: Unlimited Diesel Performance 350/200 hybrids
High-Pressure Oil Pump: Stealth SRP1.1
FUEL SUPPLY SYSTEM: Irate Diesel Performance competition system with Fuelab Prodigy pump, regulated return, Bean Machine sump
TURBO: Irate Diesel Performance T4 turbo mounting kit, Fleece Performance Engineering S468/87/.90, Irate 3-inch downpipe and intake plenums, Driven Diesel overboost annihilator
INTERCOOLER: Spearco
EXHAUST: Diamond Eye Performance 3-inch downpipe to 5-inch no muffler system
TRANSMISSION: John Wood Automotive Street Performance E4OD with triple-disc, billet stator converter, Maraging 300 input shaft, 300M intermediate shaft, cryogenically treated output shaft, 4340 flex plate, Goerend pan, Mishimoto 5R110W cooler
Suspension: Factory replacement leaf springs, rear Air Lift air springs,
One Up Offroad traction bars

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Author

Hritik Godara

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