How One Man Turned a Squarebody Burb Into a 500 Ft-Lb 6.5 Diesel Overlanding Beast

David from Willomet Motor and Fab has been turning wrenches on his 1985 Suburban since he was 14 years old, and after more than 20 years of continuous evolution, his square body has become something truly special. What started as his dad’s factory diesel family hauler has transformed into a 500+ lb-ft torque monster that proves the old 6.5 Detroit diesel platform still has serious potential when you know what you’re doing.

Based out of Houston, Texas, David runs Willomet Motor and Fabrication, where he specializes in bringing square body trucks and classic diesels into the modern era. His approach combines old-school mechanical simplicity with carefully chosen modern upgrades, and the results speak for themselves. You can follow his builds on Instagram or catch his detailed build breakdowns on his YouTube channel.

The heart of this build is a fresh 6.5 diesel long block from General Engine Products, the current manufacturer of 6.5s for military Hummers. The key upgrade here is the forged crankshaft - a crucial piece that separates this build from typical 6.5 rebuilds. David balanced the entire rotating assembly and upgraded to the latest cylinder heads with hardened valve seats and improved cooling passages between the valves. Head studs secure the top end, and main studs handle the bottom end, giving the engine the foundation it needs to handle serious power.

The fuel system is where things get interesting. David went with a DB2 mechanical injection pump from Stanadyne - specifically one of their highest-rated units with the largest plungers available. This pump flows enough fuel to support 250 horsepower and 515 lb-ft of torque, paired with large marine-pattern injectors that create a fine fuel mist in the prechamber. A 100-gallon-per-hour fuel pump from Fast Fuel Injection Systems keeps everything fed with clean diesel.

For the air side, David chose a Holset HE351CW turbo from a 2005 Dodge - a proven unit that’s been modified by Turbo Labs America with a larger exhaust housing. This turbo makes boost efficiently without creating excessive backpressure, and it sounds absolutely fantastic doing it. The compressed air flows through a modified Duramax intercooler that’s been trimmed to fit the square body’s core support, then through a Vibrant Performance intake system with a Banks air filter.

The cooling system gets serious attention because managing heat is critical for any high-performance diesel. David installed a Ron Davis dual-pass radiator with dual 14-inch brushless fans, plus separate oil coolers for both engine and transmission. He even added a steam tube setup borrowed from LS engine technology to prevent hot spots in the rear cylinders. A coolant filter keeps sediment out of the system, and dual alternators provide plenty of electrical capacity for all the fans and accessories.

This Suburban isn’t just a dyno queen - it’s David’s daily driver and adventure vehicle. The truck weighs in at 9,500 pounds fully loaded and rides on 40-inch Maxxis Razr MT tires mounted to KMC bead locks. A Magnum transfer case from Offroad Design provides multiple gear ratios, while custom rock sliders and skid plates protect the undercarriage. The suspension uses coilovers with custom towers that David fabricated himself.

Recent upgrades include a full overlanding setup with a ROAM Adventure Co rooftop tent and 270-degree awning. The Vagabond XL tent provides comfortable sleeping quarters 8 feet off the ground, while the awning creates shade and weather protection anywhere you stop. ROAM’s case system keeps all the camping and recovery gear organized and easily accessible.

David’s honest about the costs involved - building a 6.5 diesel to this level requires about $14,000 just for the engine components, balancing, and fuel system. That doesn’t include the custom fabrication work, cooling system upgrades, or any of the chassis modifications. But for David, the investment was worth it to create what he considers the ultimate 6.5 diesel build.

The truck burns fuel so cleanly that even under full throttle in soft sand, the exhaust goes from black to light gray as the turbo spools up. That’s the sign of an engine that’s burning every drop of fuel the injection pump delivers - exactly what you want to see from a well-tuned diesel.

David admits this will be his last 6.5 build. After proving what’s possible with the platform, he’s ready to move on to other projects. But this Suburban represents something special - a father-son build that evolved over two decades into a truck that connects David with the broader off-road community. It’s proof that with enough knowledge, patience, and willingness to do things right, even an old Detroit diesel can make modern power while maintaining that mechanical simplicity that makes these engines so appealing.

Whether you’re running trails in Moab, crossing Nevada on the NVBDR, or just need a reliable truck that makes serious torque, David’s approach to building the 6.5 diesel shows what’s possible when you combine old-school engineering with modern upgrades. The result is a truck that’s both capable and reliable - exactly what you want for serious off-road adventures.