Although Brian’s previous 5.21-second eighth-mile at 137 mph and 9.28-second trip through the quarter-mile in 2018 had already earned him the honor of owning the world’s quickest 7.3L-powered truck, he broke into the 4s in June of 2019. After cutting a .488 light and grabbing a 1.20-second 60-foot, Brian collected his first 4-second time slip at the end of the track (the previously-mentioned and current best, 4.92 at 144 mph). At the next two ODSS events, he would put up a 1.15-second 60-foot, followed by a 1.14-second 60-foot—evidence that 4.80s should be obtainable at the current power level.

101-PSI Boost, 1,700HP, and 4-Second Eighth Miles: Inside a Wicked-Fast Pro Mod OBS Ford
How exactly does a 351ci Windsor-powered farm truck end up being the fastest 7.3L-powered truck in existence? It starts with an owner who thrives under pressure, embraces an uphill challenge, and possesses an unquenchable thirst for speed. Believe it or not, former professional motocross racer and avid drag racer Brian Gray picked up this once four-wheel drive ’96 F-250 for $1,800 to use as a cheap daily driver in order to afford his first home. A short while later, after familiarizing himself with the 7.3L Power Stroke with his work as a diesel mechanic at the local Ford dealership, Brian decided to swap one in place and start tinkering.

When beating up on local 6.4L owners and the occasional Corvette got old, Brian lowered the truck (it sat on 46-inch tires at the time) and proceeded to wear out some 383ci Mustangs in area street races. A few years ago, Brian pulled out all the stops, and the ¾-ton OBS went under the knife for what was initially a Pro Street build. Then the decision was made to scrap what was left of the factory frame and go full tube chassis, get the truck into the 3,500-pound range, get the chassis certified to run 7.50s, and prep everything for battle against the nastiest diesel Pro Mods in the country.

It’s been a long and winding road to get here, but now things are really starting to click. In conjunction with his own business—Gray’s Diesel Performance—Brian is proving that plenty of untapped potential still exists in the old, HEUI-fired V-8, with many of the parts found in his Pro Mod being directly usable in any 7.3L engine. The following walk-around occurred shortly after Brian turned in a best-ever, 4.92-second eighth-mile pass at 144 mph. It was made with a 7.3L Power Stroke that sports the factory-based cast-iron block and heads, a big single turbo and nitrous, and steel doors with roll-up windows. If what Brian tells us is true (and we have no reason to doubt him), look for this ground-breaking OBS Pro Mod to dig even deeper into the 4s in the near future.

Whether you’re familiar with the 7.3L Power Stroke or not, this one is unlike anything you’ve ever seen. However, it’s not because the front-mount turbo, custom headers, and trick intake make the engine look different. Rather, it’s because a lot of the 7.3L’s original design remains. Though its water jackets have been filled, the factory cast-iron block is still being employed. And even though the crankshaft has been zero balanced, it’s the original piece first installed in 1996. Notable short-block upgrades include a girdle that, in conjunction with ARP main studs, ties all the main caps together, off-the-shelf Hypermax Engineering forged-steel connecting rods, and billet pistons from Diamond Racing.
Despite the recent success running 4-second passes, they have taken their toll on the factory 7.3L crankcase. Having split two blocks in a matter of weeks, Brian and his crew upgraded to a Hypermax bed plate, and they may even try to obtain one of the company’s readily-available compacted graphite iron blocks or source a billet-aluminum block over the long-term. A recent sponsorship from CP-Carrillo also means that Brian will be trying out a new long-rod and piston combination in the future as well.
Underneath the TIG-welded, PSP Diesel valve covers you’ll find a worked-over-yet-factory-based cylinder head on each bank. The Stage 2 competition heads from Swamps Motorsports feature 5-axis CNC porting, beehive valve springs, and attach to the block by way of ARP head studs. Brian designed his own camshaft to match the higher flowing heads, which he believes is one of the key reasons the engine is as powerful as it is (more than 1,800 hp at the crank on nitrous).
Other indispensable components in Brian’s horsepower-making puzzle are the individual runner intake manifolds. The aluminum manifolds entail 2-inch diameter runners and are the perfect complement to the engine’s ported heads and properly-spec’d cam. Brian believes this style intake forces all cylinders to contribute similar horsepower rather than the middle cylinders producing a disproportionate amount of the overall horsepower, which is the case on most 7.3L mills.
High-flow headers and up-pipes are a big part of driving the massive 88mm Garrett turbo Brian runs. The custom-fabricated headers route exhaust gasses to a set of one-off, bellowed up-pipes, which feed the T6 divided exhaust collector that mounts the turbo.
You know an engine is serious when you spot a dry sump oil system, and Brian’s 7.3L is no different. The setup that’s employed on Brian’s 7.3L incorporates a 3-stage Peterson pump, which is to say it features two scavenging stages and one pressure stage. Maintaining adequate oil pressure at any rpm is the name of the game for any high-horsepower competition engine to survive a harsh racing environment, and this pump supplies 150 psi cold and 100 psi throughout the course of a 4-second pass.
Don’t be misled by the mismatched paint on the truck’s exterior—the fabrication work performed on Brian’s Pro Mod is top-quality. Here you can see the headers transitioning into bellowed up-pipes at the front of the chassis. Race Part Solutions clamps are used throughout the engine’s exhaust (V-band) and intake (dual-seal) piping to rule out boost and drive pressure leaks while at the same time offering some flexibility in the intake plumbing.
And you thought HEUI technology was dead. Thanks to Full Force Diesel’s dual HPOP system, you’ll find two high-pressure oil pumps sitting at the front of the lifter valley. The two stock displacement HPOPs combine forces in supplying more than adequate oil volume to a set of hybrid injectors that Brian built himself. Fitted with 7-hole, 400-percent over nozzles, the big hybrids flow 405ccs worth of fuel on his test bench. At full tilt, injection control pressure (ICP) holds steady at just under 3,200 psi. In the future, Brian tells us he may entertain the idea of testing a pair of modified HPOPs.
The engine’s induction needs are met by a GTX5533R Gen II from Garrett. This version features the 88mm inducer compressor wheel, which flows an obscene 172 lbs/minute (roughly 2,460 cfm). The other end of the shaft (the shaft itself rotating inside a dual ball bearing center cartridge) turns a 102mm (exducer) turbine wheel within a T6 divided, 1.37 A/R exhaust housing. Leaving the starting line, the massive GT55 is already pushing 68 to 70 psi of boost. Down track, peak boost climbs to exactly 101 psi.
In a pinch, Brian and crew have had to run the 85mm version of the GTX5533R shown here. During the 85mm unit’s short tenure aboard the 7.3L, no drop in power was detected. In fact, while it was handling induction duties Brian experienced his second cracked block in less than two months.
It’s no secret the 7.3L’s injection system lags behind what modern, common-rail systems are capable of, but Brian makes up for that by spraying a boatload of nitrous. Through his use of a progressive Nitrous Express system with two Lightning 375 solenoids and eight .78 jets arranged throughout the intake runners, the truck consumes an entire bottle of N2O per pass—and sometimes a little bit of what’s in the second.
Two 12-pound Nitrous Express bottles sit behind the fuel cell in the bed, complete with dual NX bottle heaters to keep pressure up. A single, .78 spool jet helps bring the turbo to life quickly during staging, and a Maximizer 5 controller (also from Nitrous Express) brings the giggle gas on progressively. Being that the engine doesn’t benefit from the use of an intercooler, the cool, dense dose of oxygen that mixes with the incoming compressed air leaving the turbo is also used to cool intake temps and keep EGT from cresting 2,100 degrees.
In addition to running a Heatshield Products turbo blanket on the exhaust housing of the GT55 to aid spool up, Brian has also invested in making the compressor side more efficient. Partnering with Line 2 Line Coatings, the compressor housing was treated to the company’s patented abradable powder coating, which tightens up the tolerances between the housing and compressor wheel. Being of an abradable material, the powder coating is designed to wear off with no ill side-effects should the compressor wheel and housing ever make contact.
This was the latest addition to the Gray’s Diesel Performance Pro Mod when we bumped into Brian at the Scheid Diesel Extravaganza. The overhead switch panel came from Billet Automotive Buttons. Not only does it simplify pre-race tasks, but its unique button labeling helps break up the all-business mood that often consumes the cab.
As many other Pro Mod competitors have done, Brian turned to the venerable TH400 transmission to get him down the track. Brian’s was built by Proformance Racing Transmissions and features a trans brake, CO2-actuated Precision Performance Products air shifter and a bolt-together, zero drag, lock up torque converter from SunCoast. To date, SunCoast’s billet, re-stallable converter has provided the best results in containing the truck’s low rpm power. To make the task of driving easier, Brian uses a shift timer. This allows him to simply pilot the truck without watching rpm or anything else.
Built by Dutchman Axles to handle plenty of abuse, the Ford 9-inch benefits from a Strange Engineering center section, axle shafts, and a spool. Inside the differential, a 2.73:1 ring and pinion out of a Top Fuel dragster provides the exact gearing Brian needs to maximize his efforts through the eighth-mile. The rear drive shaft is a lightweight, carbon fiber piece
On the tuning side of the equation, Brian works with Jelibuilt Performance to dial in the truck’s factory PCM, while Swamps Motorsports supplied the high voltage IDM (shown). That’s right. No stand-alone computer or anything fancy, just the original TDE0 automatic transmission PCM the truck left the factory with. Jelibuilt tunes the PCM through the use of Minotaur software and a Hydra Chip from Power Hungry Performance. Brian tells us that during the truck’s violent launches—where 2.5Gs are experienced in the midst of 1.15-second 60-foots—the chip nearly backs off the PCM’s circuit board.
A parachute becomes mandatory once a Pro Mod surpasses 150-mph in the eighth-mile—which in Brian’s case could happen very soon. Also notice the fuel filters in this image. They’re part of a 220-gph fuel system from FASS. Regulated to 110 psi at idle, the high-flow, low-pressure system maintains 70 psi to the injectors going down the track.
Interestingly enough, the only fiberglass component on Brian’s OBS is the front clip. And while the doors are now made of carbon fiber, on the truck’s 4.92-second pass they were still steel, complete with roll-up glass windows. The front windshield and back glass on the truck are made of Lexan. On race day, the old Ford tips the scales at 3,550 pounds with Brian strapped into his Kirkey race seat.
Although Brian’s previous 5.21-second eighth-mile at 137 mph and 9.28-second trip through the quarter-mile in 2018 had already earned him the honor of owning the world’s quickest 7.3L-powered truck, he broke into the 4s in June of 2019. After cutting a .488 light and grabbing a 1.20-second 60-foot, Brian collected his first 4-second time slip at the end of the track (the previously-mentioned and current best, 4.92 at 144 mph). At the next two ODSS events, he would put up a 1.15-second 60-foot, followed by a 1.14-second 60-foot—evidence that 4.80s should be obtainable at the current power level.

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