Steve Ortner’s Cummins-Swapped, 1,500-HP H1

There is no denying the allure of a Hummer. They might’ve come with the undesirable 6.2L and 6.5L IDI’s back in the day, but the looks, capability and wow-factor of the military-derived H1 make it infinitely desirable. And for Steve Ortner, a longtime fan of the H1 who has amassed a small collection of them, replacing the original underpowered oil-burner isn’t a problem. In addition to his vertical wall-scaling, Cummins-powered 2-door and LSX 454-equipped versions, he just finished reworking this ’94—and the diesel industry is rightfully on fire about it. The menacing Hummer sports a 12-valve Cummins with a 6.7L block, a 14mm P-pump, big compounds, and makes somewhere in the neighborhood of 1,500 hp. The 36-inch paddles say it’s a regular at the dunes, too. Trust us, this Hummer is king of the sandbox.

Even though he has a common-rail Cummins-swapped Hummer in his collection, Steve Ortner is an old-school kind of guy—hence the mechanical 12-valve that powers this one. Assembled at Steve’s CNC and fabrication shop, Mountain Machine in Belleville, Michigan, nothing was left to chance. A 6.7L Cummins wet block from Hamilton Cams serves as the foundation, with ARP 14mm main and head studs, Wagler Competition Products forged-steel rods, fly-cut billet-steel Diamond Racing pistons, and a 188/220 Hamilton cam all residing in the bottom end. The OEM cylinder head was treated to measurable CNC-porting, oversize intake and exhaust valves, and benefits from a clamshell style, individual runner intake manifold Steve fabricated at his shop.

The Snowball Effect

A ragged-out, beat up Hummer when he obtained it for just $12,000 from its 20-something previous owner, Steve’s ’94 has been a work in progress for many years, and he’ll be the first to tell you that one thing led to another until the build snowballed out of control (in a good way). Now, his work-of-art not only serves as a means of scaring any passenger brave enough to climb aboard it, but it’s also the ultimate advertising tool for his company, Mountain Machine. “It’s a rolling business card,” he told us. “You can see what we did here with the Hummer, which means we can do your custom fab and machine work, too.”

Capable of providing the kind of fueling that Pro Stock truck pullers are looking for (2,000-hp or more), the 14mm P7100 from Farrell Diesel Service can flow more than 1,000 cc’s of fuel. So far, Steve has yet to find a need to go beyond the current 870cc setting. The P-pump’s timing is set at 28-degrees of advancement and it sports 5,000-rpm governor springs. Oversized, .120 injection lines route fuel to a set of Scheid Diesel injectors with dual-feed bodies and 5x.025 nozzles. The pump and injector combination brings so much fuel to the table that fuel is actually used to cool EGT rather than raise it.
There is nothing small about the compound turbo arrangement that feeds the Cummins, with enough air on tap to easily clear 1,500 hp. Things get started with a GTX55/Holset hybrid from Apex Turbo. The one-off atmosphere charger utilizes a hub-free compressor wheel packing a healthy 110mm inducer size, a 114mm turbine wheel on the other end of the shaft, a Holset exhaust housing with a V-band inlet, and a triple ball bearing center section and back plate from Mountain Machine. The high-pressure turbo is an Apex S486 and bolts to a T-6 Steed Speed exhaust manifold.

6.7L Block, 12-Valve Head

When you’re looking to make four-digit horsepower, it pays to start with a solid foundation. For that, Steve took receipt of a 6.7L Cummins block from Hamilton Cams. To avoid having to wait around for the engine to cool down, he went with Hamilton’s water jacketed version. Sticking with other prominent names in the industry, forged-steel rods were sourced from Wagler, the fly-cut, billet-steel pistons came from Diamond Racing, and Hamilton’s 188/220 camshaft got the call for valvetrain operation. ARP 14mm main and head studs are also employed, as are the company’s ½-inch rod bolts. A worked-over 12-valve head—treated to CNC porting, oversize valves, and an individual runner intake manifold—allows the Cummins to breathe freely.

In order to integrate the P-pump with the 6.7L block, Steve designed and machined his own billet-aluminum front gear housing at Mountain Machine. Here, you can also see that it accommodates a gear-driven Waterman Racing fuel pump, which supplies the P7100 a minimum of 65-psi at all times.


If you were wondering what kind of axles and suspension are in use on this monster, the answer is “pretty much all stock.” Aside from coil springs and shocks from Rod Hall Racing, the original front and rear double A-arm independent suspension, AMC 20’s with portal gearing, and 242 AMG transfer case remain—and have survived the Cummins’ wrath so far. The front ring and pinion didn’t, which meant both diffs were treated to upgraded 2.73:1 gears from Yukon. The 4L80-E transmission is still employed, too—albeit one that’s been beefed up by nearby Accurate Transmission. The GM four-speed sports all billet shafts, an 1,800-rpm stall, triple-disc Yank converter, and a full manual valve body.

Well North of 1,200 HP

While the Cummins initially made 1,200 hp on Apex Turbo’s engine dyno—an apparatus that usually sees big cube, mega-horsepower tractor engines—that number was achieved before the 14mm P-pump and water-meth were in the mix. EGT increased to a toasty 1,800 degrees, too. Now, EGT seldomly crests 1,200 degrees and a boatload of fuel is on tap. The way things sit at the moment, Steve believes the engine builds 1,400 to 1,500 hp.

The 36-inch Sand Blasters do more than provide an ultra-aggressive stance for Steve’s Hummer, they perform as advertised, often slinging sand 50-feet behind the rear bumper. The paddle tires were grooved by Scott Carlson of DuneLand Off-Road Center and mount to 17×9-inch Monster beadlock wheels from Raceline.

14mm P-pump and 5×25’s

To integrate the mechanical Bosch P7100 to the 6.7L block, Steve designed and manufactured his own billet-aluminum gear housing for the front of the Cummins. And not only does the cosmetically-pleasing cover accommodate a 14mm P-pump from Farrell Diesel Service, but it also includes a provision for running a gear-driven fuel supply pump, which in this case is a high-flow unit from Waterman Racing. Downwind of the big P-pump, Steve runs a set of dual-feed, 5x.025 injectors from Scheid Diesel, which receive plenty of fuel courtesy of six .120 injection lines, also from Scheid.

Steve’s refusal to do anymore cutting on the H1 than was necessary is precisely how it ended up with a massive atmosphere turbo poking out of the hood. Believe us, the fit and finish of the turbo and stack protrusion is absolutely flawless. While Steve’s turbo combination has produced 100-psi of boost in the past, he currently has the system wastegated to limit boost to 70-psi. Both 45mm external TiAL gates were obtained from industry-friend, Mike Wysowski, and they sit in the hot-pipe that links the S486 to the GTX55/Holset hybrid.

110mm Over 86mm Turbos and Water-To-Air Intercooling

As if the injection system wasn’t serious enough, the turbo arrangement takes things even further. Not only does the atmosphere charger stick halfway out of the hood, but the Apex Turbo-built charger conceals a 110mm compressor wheel, along with the company’s hub-free design for optimum airflow. On the Steed Speed T-6 exhaust manifold, an 86mm S400 brings the two-stage setup to life. To cap boost at 70-psi, dual 45mm TiAL external wastegates are plumbed into the system’s hot-pipe. Intercooling comes by way of a Frozen Boost water-to-air unit, with the ice box and circulator pump located in the rear of the Hummer.


Mostly Stock Axles, Fully-Built 4L80-E

Many are surprised to find that Steve retained most of the H1’s original suspension and driveline. The front and rear independent suspension, AMC 20 axles and geared hubs at each corner are all stock, as is the factory 242 AMG transfer case underneath. The only forced differential upgrade thus far has been the addition of a front ring and pinion from Yukon, with the rears being swapped at the same time. To help navigate the dunes more comfortably, Steve installed coil springs and shock absorbers from Rod Hall Racing, but he original upper and lower A-arms survive. As for the transmission, Steve stuck with the 4L80-E, but for obvious reasons it was thoroughly reinforced to handle the Cummins’ power. Accurate Transmission pieced the four-speed together with billet shafts, an 1,800-rpm stall converter from Yank Performance, and a full manual valve body.

A Frozen Boost water-to-air intercooler keeps intake temps on ice and limits EGT to a manageable 1,200 degrees. The rest of the intercooler system, as well as the water-meth tank and the radiator for the engine, can be found in the back of the Hummer. That shiny piece you see positioned between Vibrant quick release clamps on the driver side water-to-air piping is Steve’s cable-operated air guillotine. Below it sits a blow-off valve, which is very important in eliminating the turbo surge that’s typically experienced when digging through the sand and having to back out of the throttle quickly.
Projects like these never really end, right? Never satisfied, Steve plans to replace the ported factory-based cylinder head with this Hamilton War Head soon (maybe even by the time you’re reading this). Capable of flowing more than double what a stock 12-valve head can, you can bet it will probably free up even more horsepower.

Catch Him At The Dunes

So why is Steve so big into Hummers? “I was into square body trucks for forever, but I always thought of a Hummer as the quintessential American truck,” he told us. “I mean, it’s the John Wayne of trucks.” It’s pretty hard to argue with that, and it’s even harder when you’ve got a 1,500hp beast like this in your stable. This summer, Steve plans to terrorize Silver Lake Sand Dunes with it, along with hauling it to the Ultimate Callout Challenge in Indy. If you find yourself at either of these two locations this summer, be on the lookout for the baddest Hummer in the land. It’ll be the one with a hood stack and a massive turbocharger peeking through the hood…

“It’s the John Wayne of trucks.”—Steve Ortner

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