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This isn't the first time John Martinson has thrashed on a Fiat 1100 fitted with a Honda engine and Unimog axles. He wheeled a similar rig during Four Wheeler's 2014 Top Truck Challenge, where despite being an alternate he demonstrated loads of vehicular competence tackling the competition's many obstacles. We recently caught up with Martinson during the 2023 King of the Hammers event in Johnson Valley, California, where he showed off one of the latest creations in his stable of freaky, Fiat-based extreme off-roaders.

Honda Power Up Front

Martinson told us weight is why he selected the Honda K24A2 engine to power his monster Fiat. The 2.4-liter inline-four was treated to Manley Performance connecting rods, Arias pistons, upgraded head studs, and a Garrett GTX3076R Gen II turbocharger. He fabricated the turbo manifold himself using schedule 80 stainless steel. Even with its hand-built turbo setup and exhaust, the engine only adds 305 pounds to the front of the chassis. He loves the engine's low-end torque and 8,000-rpm redline, and he believes its output to be in the neighborhood of 550 ponies on pump gas.

Unimog Portal Axles for a Fiat

High clearance is the game in the hardcore off-roading arena, and Unimog portal axles wrote the rule book. Gearboxes at each end of the axle bring the axle reduction ratio up to 6.5:1 for maximized low-range grunt. Portal axles also raise the centerline of the axle in relation to the wheel's center, offering further improvements in the drive-clear-over-rocks-without-touching-them department. Bonus points: Both axles under the Fiat 1100 can be steered thanks to a Stazworks hydraulic rear-steer system.

43-Inch Tires

The Interco Super Swamper TSL SX tires measure 43x14.50R17, and get this—they're not even the largest tires he runs on the 4x4. In his home state of Washington, the snow gets deep. Driving the Fiat in the deep powder requires 49-inch tires fitted with just under 1,000 studs apiece and extremely low tire pressure in order to stay afloat.

Custom-Built Suspension

Wide Open Design aluminum links make up the four-link suspension that locates the Fiat's Unimog axles. Radflo 2.5-inch triple-bypass shocks and coilovers keep axle movements in check, and 3-inch bumpstops are there to minimize harsh bottom-outs. Martinson said his rig also has 16 inches of suspension travel at each corner.

Powertrain and Protection

Downstream of the turbocharged Honda mill there's a venerable TH400 three-speed automatic transmission, an Advance Adapters Atlas four-speed transfer case, and a UHMW plastic skidplate. Compared to steel or aluminum, the UHMW skidplate is designed to better help the vehicle slide over obstacles.

Interior and Custom Fabrication

All tubing was bent and rolled in-house using a Rogue Fabrication bender and a SWAG Off Road roller. Looking at the interior, it's easy to see how hard the Fiat's been 'wheelin. Because of this, Martinson's recommendation to anyone driving 4x4s on the trails: Wear a helmet!

Fiat Conquers Backdoor

Martinson piloted the Fiat up Backdoor, one of Johnson Valley's gnarliest obstacles—and came back for more. The vehicle's combination of a steering rear axle, wheelbase, and weight among other factors allowed him to easily climb the rock face to the amazement of onlookers. One attempt, however, shook loose the Fiat's trunk hatch, which he was able to reattach. If you want to see the Fiat and other incredible machines in action out at Johnson Valley, you can watch them climbing Backdoor HERE.