A 1,000-HP Diesel in a Military Wrapper
Steve Ortner, of Belleville, Michigan always wanted a Hummer. When he finally got the chance to buy a ’94 civilian-spec Hummer H1, he was ecstatic. But there was a problem. “The Hummer had a naturally aspirated 6.2L engine, and it was so, so slow,” Ortner exclaimed. “There were times on hills when I was unsure if it would make it up to the speed limit!” He definitely had the vehicle he’d always wanted—but it was powered by the wrong engine.

12-Valve Transplant

“I had always liked stuff with power and reliability, so the 5.9L 12-valve Cummins was an obvious choice,” Ortner said. After acquiring the engine from an old Fed-Ex truck, he was off to the races. Since he knew he wanted a lot of power, he started with the engine block and worked his way up. The Cummins block was fitted with 14mm ARP main studs and a modified girdle, based on an Industrial Injection Gorilla Girdle. He kept the factory crank, but added connecting rods from Wagler Competition Products. A 188/220 camshaft from Hamilton Cams was also added, and the block was machined to accept 14mm head studs. After the bottom end was assembled, Ortner opened up the Hamilton Cams catalog to search for street heads, a valve spring package, and pushrods.

Performing a Cummins swap is hard enough, but Steve Ortner went the extra mile and built his 5.9L 12-valve for monster power. The engine pushes approximately 1,000 hp and 1,700 lb-ft of torque through a J&H 4L80 to the Hummer’s all-wheel-drive system.
Since the Hummer came from the factory with a diesel powerplant, there was a decent amount of room for the swap. Many parts like the engine mounts and transmission adapter, were made in Ortner’s shop, Mountain Machine.
Reliability was priority number one, so Ortner reinforced his engine everywhere he could, with ARP studs in the mains, the rods, and the head. He even went a little further with the head studs, choosing ARP’s Custom Age 625 material to prevent potential issues at high boost.
The number of custom parts on this Hummer is practically endless. Whether you’re looking at the engine, the cooling system, or the drivetrain, there’s something special everywhere you look.
Since he planned for the engine to spend a lot of the time in the sand, Ortner had to make sure to size the turbos correctly. He didn’t want to go with a big single due to the lag, so he instead went with a compound setup that starts with a 66mm S300 turbo from BorgWarner.
The fueling system is perhaps the most over-built component of this Hummer. It starts with the fuel getting sent to the engine via a 220-gph FASS pump, where it’s then fed to a Farrell Diesel Service 13mm P7100 injection pump, and then Power Driven Diesel 5x.025-inch injectors. All told, Ortner figures he has about 1,500 hp worth of fuel onboard.


While a single turbocharger would’ve been the easy way to go, Ortner was more concerned with response and power, directing him more towards a compound turbo. With a high-rpm capable engine, Ortner went with a 66mm turbocharger as his smaller turbo and a monster 88mm BorgWarner SX-E for the larger turbo. He built a custom intercooler from a bare core and jacked the fuel to the stratosphere with a Farrell Diesel Service 13mm P7100 pump, Power Driven Diesel 5×0.025-inch injectors, Scheid Diesel 0.120-inch injection lines, and a FASS 220-gph lift pump. Estimated horsepower is somewhere around 1,000 hp even with the 13mm pump turned down.

Power Transmission

Transmissions can be a troublesome part of diesel swaps, but in this case, Ortner lucked out. A GM 4L80E easily fit in the transmission tunnel, and he was able to adapt the Cummins engine to the transmission via an adapter plate of his design. A Cummins-to-GM flexplate was also used as the final piece to hook everything together. GM 4L80E transmissions are desirable for diesels because they use an overdrive gear, they’re relatively light, and they’re extremely durable. For a racing gearbox that could handle the engine’s immense torque, Ortner dropped the electronic “E” and went with a J&H full manual valve body and performance transmission. The 4L80 features raised line pressures, aftermarket shafts, as well as a tough Yank Performance torque converter that stalls at about 2,200 rpm. Used in off-road race trucks, this converter is one that’s built to handle abuse.

The larger turbo is an 88mm with the new SX-E technology from BorgWarner. It’s the primary air mover in the system, producing about 80-85 psi of boost. Ortner says the Hummer really starts to come alive at 2,500 rpm and will pull all the way to 4,500-5,000.
The intercooler is just one of many pieces of the puzzle needed for the Cummins swap. Ortner wasn’t able to find anything to fit the bill from any catalog, so he bought an intercooler core that roughly matched the flow specs from the big turbocharger. He then made necessary changes by fabricating end tanks that would fit the engine bay confinements on the Hummer.
An onboard air system is a big part of Ortner’s creation. The lockers and tires all need to be aired up and down as well as activated and deactivated for the sand, so he installed an ARB air compressor system to get the job done.
The suspension on a H1 Hummer is truly unique and one of the toughest independent suspensions around. The battle-tested design is AWD (all-wheel-drive) without a 2WD option, and this one has been supplemented with a Rod Hall long-travel kit.
The Hummer’s rear axle was fitted with an ARB air locker to help with traction. Unlike virtually all diesel pickup trucks, the rear suspension is an independent design and is only able to survive because of its incredible strength. Ortner reports that the factory gearing works well with the diesel thanks to the engine’s high-rpm operation and the overdrive transmission.
The first clue that this Hummer is diesel-powered is the 5-inch exhaust stack, which is routed up and out of the port where the factory air cleaner used to reside.


The suspension was another area where Ortner turned to the off-road racing industry, considering most parts stores don’t carry lift kits for Hummers. He wanted his H1 to be fully capable, so he went with a Rod Hall Products long-travel spring and shock package. It was designed to give the truck a couple of inches of lift along with useful travel. The rest of the drivetrain was also reinforced, with a transfer case from an armored Humvee and ARB front and rear air lockers that work with the factory gearing. Ortner also up-sized in the wheel and tire department with 37-inch Pitbull Rocker XOR tires mounted on 17×9-inch Method Race Wheels beadlocks.

Dream Truck

When he finished building his innovative Hummer, Steve Ortner now had enough power to pass cars on the highway—and just about everything else. He spends a lot of time in the sand where the Hummer shines, as its independent suspension, huge wheels, massive tires, and immense diesel torque form the perfect combination. So what’s next? “I need to find a four-wheel-drive dyno in the area and start leaning on it,” he described. Ortner also attracted enough interest in his personal Hummer conversion that he’s now building examples for customers. “I had a lot of friends help out with this one,” he replied. “Casey Curtis, Ed Larsen, Carl Sparks, and Chris Reiter. We all decided we wanted to do more. There are about three in the shop right now—and I don’t see things slowing down any time soon.”

Estimated horsepower is now somewhere around 1,000 hp.

The front bumper is a Steve Ortner creation and is augmented with a set of KC HiLites LED clusters and a 15,000-pound Warn winch.
As with the front, the stylish rear bumper was fabricated at Ortner’s shop and is just one of the many other handmade parts on this vehicle.
With a small fortune invested in the engine and transmission, Ortner wanted to keep an eye on everything. He used the factory Hummer pillar to mount four AutoMeter gauges, plus a center tachometer that lets him keep the engine in its sweet spot.
Custom black vinyl was custom cut for this Hummer and covers virtually every square inch of its interior.
Even the badges inform that this Hummer isn’t to be messed with.
Ortner went tall by wide for his tire choice, and the aggressive 37×12.50-inch Pitbull Rocker XORs mounted on 17×9-inch Method Race Wheels beadlocks are designed more for the sand than anything else.
This cool central tire inflation system (CTIS for short) allows Ortner to air the tires up and down without ever leaving the comfort of the Hummer’s cabin.


ARB 4×4 Accessories

ARP Diesel

AutoMeter Competition Instruments

BorgWarner Turbo

Farrell Diesel Service

FASS Diesel Fuel Systems

Hamilton Cams

Industrial Injection Diesel Performance

J&H Performance


Method Race Wheels

Mountain Machine

Pit Bull Tires

Power Driven Diesel

Rod Hall Products

Scheid Diesel Service

Wagler Competition Products

Warn Winches

Yank Performance

Leave a Reply

Your email address will not be published. Required fields are marked *

You May Also Like

The Long Road

The truck of our dreams is rarely built overnight. And for some of us, it unfolds over the course of years rather than months. For Bryan Woitas and his ’02 Chevrolet Silverado 2500 HD, nothing…


These trucks are about as low as you can go before your borderline scraping the ground. These diesel trucks took a different approach to modifications as typically most diesels are lifted with…