The Finale of the Mad Maxxis Off-RoadRunner

    Part 4: We Finish Our 4x4 Muscle Car for the Apocalypse

    Fred WilliamsWriterJessica WalkerPhotographer

    What started out as a harebrained idea turned into the coolest 1973 Road Runner you’ve ever seen in Petersen’s 4-Wheel & Off-Road. This rust bucket was destined for the giant junkyard in the sky or for some expensive restoration before we drug it home and made it into our own version of a Mad Max muscle car. The car was built in collaboration with Maxxis tires for an episode of Dirt Every Day, our YouTube show that you need to check out. The episode will be live December 22, 2015, so check it out.

    In addition to Maxxis we also worked with Cummins who brought the new 5.0L V-8 diesel to the Off-RoadRunner recipe. We followed the new diesel engine with an Allison six-speed automatic from ATS and an NP205 from Off-Road Design, both built in Colorado. To make the engine and transmission talk together we had a bunch of help from Cummins, Powertrain Control Solutions, and Destroked.

    Our setup may not be 100 percent doomsday ready, but it sure is fun to drive. The power drops to a Dynatrac ProRock 80 rear axle and Currie modified Dana 60 front axle. Internal parts come from Detroit locker, ARB Air Lockers, Dana-Spicer, G2, Reid Racing, EBC brakes, and others. The transfer of torque is done through JE Reel driveshafts and steering direction chosen by a full hydraulic steering from the Off Road Connection.

    The beefy components allowed us to hammer hard on the car, and you’ll see it all on the episode of Dirt Every Day. Go check it out on the Motor Trend channel on YouTube.

    The front axle under the Off-RoadRunner was an old Dodge Dana 60 stuffed with 4.56 G2 gears, an Eaton Detroit locker, Currie G2 axleshafts, G2 selectable hubs, bearings and seals from Spicer, and Reid Racing knuckles. The full hydro steering was the fastest steering setup we could build (we built the whole car in five weeks at Chappelle’s Exhaust and Kustom Shop), and although it’s not our first choice for a street-driven car, it’s perfect for our dirt-head Plymouth.

    Mad-Maxxis needed something silly and sinister for headlights. We opted for these red HID, LED, and projector combo lights from HIDProjectors.com that allow us to vary the front light colors with a remote control. We doubt that running flashing red and blue lights is 100 percent street legal, but the reds give it a very mean look and yet keep the car fun and silly.

    The AirRaid air filter when attached to the Cummins intake shot straight up through the hood. We found that part of the underdash HVAC ducting that we had removed earlier in the build made a perfect junkyard hoodscoop. Yep, that’s the defroster ducting recycled.

    The Cummins runs clean—sorry, no rollin’ coal—but it’s also pretty well uncorked. The single exhaust from the single turbo dumps through and enlarged rust hole on the passenger side. It sounds great. Nothing but turbo tunes and big-tire whine.

    The car needed some supporting company logos, but decals didn’t seem cool enough. We sandblasted names in the side windows to give props to those great folks who supported our wacky project car. This car is a hoot to drive and would make any doomsday marauder proud to be seen in it.

    Who in their right mind would put white racing seats in a dirt car that has little to no floor and will never have the windows rolled up, much less a car that has a giant stinking, often-leaking diesel tank in the back seat? We would! And they are perfect, super comfy, and were dirty before we left the shop. We also added belts and harnesses to protect us if we got dumb. A PowerTank CO2 tank powers the rear air locker for simplicity, and the big purple transmission is from ATS.

    The wiring in the Road Runner is a mixture of Cummins Harness, Allison harness, and original Plymouth, but we run everything through a Painless Performance Wiring kit to make everything easier to use. This off-road dash switch panel eventually made its home on the center console to offer easy selection of the fuel pump and starter and to engage the electric fans on the Flex-a-lite radiator, the transmission cooler from Off-Road Power Products, and the auxiliary lights.

    The front suspension uses dual 2 1/2-inch Fox air shocks for easy installation and height adjustment. In most situations we would recommend just using Fox coilover shocks because they are way better for all-around off-roading, but the air shocks fit our bill and we ran duals because we wanted more support for the weight. The orbital valve on the frame in the background is from the Off-Road Connection and tells the front end which way to steer.

    From the side you can see the muscle car rake and the full subframe we built under the Roadrunner at Chappelle’s Exhaust and Kustom Shop. The link suspension, JE Reel driveshafts, and Deaver leaf packs all work around the crown jewel Maxxis Razr tires on American Racing wheels—40s in the back, 35s up front, dual spares in the trunk. This car is insane and we love it.