1. home
  2. how to
  3. tech qa
  4. Mad Maxxis Off-RoadRunner, Part 3

Mad Maxxis Off-RoadRunner, Part 3

Power Part for the Post-Apocalypse

Fred WilliamsPhotographer, Writer

We have been turning a 1973 Plymouth RoadRunner into a Mad Max style doomsday vehicle for no other reason than it’s cool. This was a rusty old muscle car sitting in a field when we rescued it and began transforming it into the mad machine you see here. The car has no frame, just a unibody design, so we spent a great deal of time adding a subframe because it’s getting a full 4x4 conversion and a diesel V-8 from Cummins so we needed strength.

The project started with a wacky idea that snowballed when we got Ultimate Adventure crony and mad fabricator Dave Chappelle of Chappelle’s Exhaust and Kustoms involved. Then we convinced Maxxis Tire to supply its new Maxxis RAZR MT tires, and the project was off and running. Well, not running exactly, but moving towards running. Want to see how it all ends up? Look up Dirt Every Day on the Motor Trend Channel on YouTube.

The Off-Roadrunner is getting a diesel V-8, and so it needs an intercooler. We sourced a sweet unit from Mishimoto. They offer various sizes and colors, but we knew gold would be wacky enough for our build. Ignore Dave Chappelle; he’s just looking for attention.

To protect our intercooler and radiator, Chappelle added a skid made of diamond plate. We like to build doomsday cars because we can use whatever crazy material we want. We need to protect our vehicle from marauders and zombies.

This is the growl in the belly of the beast. We talked Cummins into bringing a 5.0L industrial V-8 diesel engine very similar to what is going in the new Nissan Titan. The RoadRunner has 300 hp and 540 lb-ft of torque under the hood.

Behind the Cummins we have a built Allison 1000 six-speed transmission. The bright purple paint tells you it was built by ATS performance. We had to convert the bellhousing to SAE3 bolt pattern from its factory GM bell because this trans came from the factory behind a Duramax.

There is a wild orange NP205 transfer case adapted to the back of the Allison with a Destroked adapter. The 205 came from Offroad Designs and is from a GM truck since we need a passenger front output for our front Dana 60. The transfer case has front- or rear-only options and will hold up fine to the Cummins torque.

The front Dana 60 came from a Dodge truck but got a complete rebuild. But first we took it to Currie Enterprise to get the long side tube replaced with the longest one Currie could build. We needed a wider front end, and Currie builds any axleshaft as long as possible and then matches the tube length. We delve more into the front end next time.