12 Cool Things About The Mil-Spec Hummer H1 - Popular Mechanics

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Brutish. Uncompromising. Four tons of truck with 16 inches of ground clearance in a machine as wide as a semitruck. The Hummer H1 was all of those things, and in the time since 2006, the last year this hulk sold as a production car, the collector price for these beasts has soared.

But if the O.G. Hummer wasn’t bonkers enough for you, don’t worry. A group called Mil-Spec Automotive specializes in these machines and aims to fix all the Hummer’s weak points. It meticulously restores and upgrades H1s to levels far beyond anything that ever rolled off the line at AM General.

We spent an afternoon with a quarter-million-dollar behemoth. Here’s what we discovered about it.

1

The H1’s Bodywork Is Completely Rebuilt

The Mil-Spec techs disassemble, examine, and rebuild or replace every component on these trucks. That includes the bodywork. Mil-Spec says the AM General factory joined the panels using generous amounts of seam sealer instead of cleanly welding them together. That stuff is heavy—Mil-Spec says the extra material added a lot of unnecessary weight to the truck.

Its engineers strip out all this goop and weld up the bodywork. They also replace every one of the interior panels with ones made from 6061-T6 ten-gauge aluminum sheet. Twenty-six panels are pre-fitted to the truck; the gaps are measured and adjustments are made before they are sent to upholstery. Because of all this care, Mil-Spec says, its H1s are a few hundred pounds lighter than a stock Hummer.

2

The Chassis Is Spotless

Mil-Spec doesn’t settle for repainting the frame and suspension parts. It removes and stress-tests every component, then it upgrades frame parts to handle Mil-Spec’s accessories. Once inspected, every piece of the chassis and suspension is sent out to be powder-coated. This meticulous process means the chassis will have a long-lasting, durable, corrosion-resistant paint job—not to mention an undercarriage worthy of a car show.

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There’s a 500-hp Duramax Diesel

For all its tough-guy looks and capability, the original Hummer H1 was a little lacking in the horsepower and torque department. Yes, the final Alpha editions from 2006 received a 300-hp Duramax diesel, but most H1s ran on the pokey GM 6.5-liter turbo-diesel V-8 or a weak-kneed 5.7-liter gas V-8.

Mil-Spec ditches those dismal powerplants and hand-builds a balanced GM Duramax V-8, which it claims will make 500 horsepower and 1000 lb-ft of torque. Not enough? Okay, fine. They can sell you an 800-hp version of the same engine. These engines are based on the 2005 to 2007 “LBZ” generation 6.6-liter Duramax, which has a reputation amongst diesel hot-rodders as stout motors that are receptive to performance modifications. The big diesel is paired to a six-speed Allison transmission.

The downside to all this gearhead dedication is that you’re running a relatively old engine, which lacks the latest Selective Catalytic Reduction emission controls. Push the throttle to the floor and you’ll get that satisfying rush of power and torque—accompanied by some serious exhaust smoke. On the plus side, Mil-Spec says you can put B100 biodiesel in this truck.

4

Mil-Spec Cools All the Things

By its own admission, Mil-Spec went overboard in keeping the H1 cool. The Duramax V-8 has a traditional clutch fan as well as dual electric fans to keep engine temps down. Peek under the bed to find dual transmission coolers and electric fans for the six-speed transmission.

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You Can Do Smoky Burnouts

Full disclosure: I did not actually do big, boastful burnouts in a 7,500-pound Hummer wearing 38-inch-tall rubber. But I could have. And that’s because Mil-Spec replaces the stock transfer case—which made Hummers all-wheel-drive, all the time—with a beefier unit from a Chevy Silverado heavy-duty pickup that features part-time 4WD. That case has a position for 2WD, so the rear tires are ready to roast.

6

The Dual Air-Conditioning System

The Hummer is a big vehicle inside and out. Bigness is really its defining characteristic. As you might imagine, attempting to cool that acreage on a hot day can take a while. So Mil-Spec rips out the old system and installs two (!) HVAC systems.

The new units have more powerful fans, improved heater cores (the original ones, Mil-Spec says, were prone to failure), and a larger and stronger a/c condenser. Just flip those industrial dash switches and the powerful blowers cool down the Hummer in a jiffy. For now, the fans are either on or off with no control over speed. Mil-Spec says that will change soon. The company says the stock defrosters don’t work well either. So, it ditched the idea of blowing air on glass and went with a heated windshield.

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The Interior is a Major Improvement

Inside, Mil-Spec ditches just about everything that came on a stock Hummer. Those with a sharp eye will notice some switchgear from other vehicles and a/c vents pulled from a Ford Super Duty. But much of the important stuff is new. The gauges are custom Speedhut units that were inspired by high-end watches, and the interior materials fit the truck’s rugged mission. And we dig the simplicity of the marine-grade JL Audio system and that old-school steering wheel.

The fabric soft-top wasn’t left stock either. It’s an aftermarket unit with a half-inch of foam padding on the inside to absorb noise. Mil-Spec says it has upgraded the way the top is fitted to the roof so there’s no buffeting, even at speeds above 80 mph.

8

It’s Built to Get Dirty

Mil-Spec’s HQ is in Michigan and its manufacturing is done in Kansas—both places where road salt and corrosion are a reality. The H1 body is prepared with a corrosion-resistant bedliner-type material on the outside and a thermal ceramic coating on the underside. And if you leave the top down in a rainstorm, that’s probably okay—there is no carpet on the inside to get soggy. The floor is triple layered with a sound-deadening spray and a mix of marine-grade vinyl and canvas surround the cabin. The whole package has been designed to be water-resistant.

9

Mil-Spec Has Its Own Proving Ground

The company builds these monster trucks in a massive 60,000-square-foot warehouse in Wichita, which is located on a 100-acre compound with plenty of pavement, dirt, and water. Mil-Spec says it built three test mules and abused them on and off road all over this hometown proving ground.

The team abused these mules, testing them in 120-degree heat as well as freezing temps in the dead of winter. They spent a full year breaking trucks, overheating them and even jumping them into the air. Mil-Spec put 500 miles on each truck prior to delivery to make sure the package was sound.

10

It’s Fast—for a Hummer H1

Lay into the throttle from a stop. The Mil-Spec squats on its haunches and launches hard. The makers claim a 0-to-60-mph time in the 5-to-6 second range depending on the body type, and yes, there are plenty of expensive SUVs that can match or beat that time. But those numbers are pretty damned amazing for a Hummer.

More important, the Mil-Spec H1 cooks up an incredible sensation of speed because of the sheer size and weight of the truck. The power and torque of the new engine makes the Mil-Spec feel way more nimble and athletic than any Hummer H1 we’ve driven.

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It’s a Better Beast Off-Road

On a private off-road area in Southern California, we put this H1 through its paces on some mild off-road trails. The terrain didn’t challenge the Hummer’s capabilities, but it did prove the Mil-Spec machine rides a bit better than other H1s.

The reason for that smoothness: The suspension is now set up with equal amounts of travel for compression and rebound, thanks to repositioned shock mounts. Additionally, the Mil-Spec trucks use the beefier CV driveshafts, stronger axle half-shafts from the up-armored military Hummers and have a beefed-up steering system.

As handy as it is, the Hummer’s Central Tire Inflation System is trouble-prone, so Mil-Spec leaves it off its builds. However, it does install ARB locking differentials to provide true 4WD without any drivability drawbacks on the street.

12

The Options Run Deep

The standard Mil-Spec truck costs a dizzying $218,500, including the donor Hummer H1. The truck we sampled had $30,549 in additional options ranging from the heavy-duty brush guard and rear bumper, light bars, wide-body kit with fender flares, and 38-inch tires on 20-inch wheels. Oh, and there’s the bespoke paint package too.

That’s only the beginning. A Wilwood big-brake option, long-travel “Baja” suspension and more stuff can ratchet that price closer to the $300,000 mark. Yes, Mil-Spec admits this is rarified air. And a Mil-Spec Hummer is typically the fifth or sixth vehicle in the garage of its customers. But with just a handful produced each year, there’s little chance you’ll ever see another Mil-Spec Hummer parked next to yours.

Ben Stewart

Ben is a lifelong enthusiast of anything with wheels. He has been contributing to Popular Mechanics for nearly 20 years and lives in Venice with an eclectic collection of vintage pickup trucks, muscle cars, and motorcycles scattered in various garages around SoCal.

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