If you've been following along then you know we are building a brand-new four-door Jeep Wrangler JK for this year's Ultimate Adventure trip. Plus you would already know that Ultimate Adventure is our weeklong off-road trip we do every year with a group of readers, advertisers, and friends. What you probably don't know is the scope of the enormous project we have taken on this year in order to build the Ultimate Jeep Wrangler.
Hey, there are no tires under that Jeep. In fact, there's nothing under that Jeep!
Jeeps are easily the most prevalent off-road vehicles in the U.S., so the challenge of building one different enough from all the rest to lead our UA trip is pretty daunting. Luckily we found an awesome crew to help transform our bone-stock two-wheel-drive (yes, two-wheel-drive) '07 Wrangler Unlimited into a monster off-road machine. Our first stop was at Twisted Customs in Rapid City, South Dakota, where we had a six-point cage installed last month. Twisted Customs is one of the top shops in the nation when it comes to building rock-buggy chassis, so we're confident in the performance of the cage if we need it. After that we drove the Jeep to Missoula, Montana, where we enlisted the help of American Expedition Vehicles (AEV) for the majority of the buildup. AEV is to Jeeps what Saleen or Roush is to Mustangs and Lingenfelter or Callaway is to Corvette. The folks at AEV are some of the best in taking a showroom Wrangler and transforming it into a top-of-the-line luxury trail machine. Their specialty is swapping the late-model Dodge Hemis into Jeep TJs and JKs but they also sell bumpers, wheels, and a pickup-truck conversion kit to turn your Jeep TJ into a Jeep "Brute" pickup (you'll notice some parked in the background of the photos; they're really cool). In addition to its normal products, AEV has won a few design excellence awards from Chrysler for its amazing concept cars displayed at the annual SEMA industry trade show. As you can see, AEV is a perfect choice for our biggest Jeep build ever, but we must explain this from the start. What we asked them to do to our Jeep is above and beyond anything they offer to customers, so don't expect them to be offering a kit anytime soon to swap a Cummins diesel into a brand-new Jeep Wrangler. Yes, you read that right, we are putting a massive 5.9L Cummins diesel under the hood of our Ultimate Adventure Jeep, but doing so has opened up a can of worms like no other. In fact, we were lucky enough to come across the entire drivetrain and chassis of an '06 Dodge Mega Cab that was on its way to the crusher, so rather than dropping the Cummins into the 1/4-ton Jeep frame, we instead chopped and squeezed a shortened Dodge frame under the freshly channeled JK body. And here is the best part: As this is being written the Jeep is sitting in AEV's shop, in pieces, and there is less than a month until it makes its debut at the start of Ultimate Adventure. Situation normal; time to get back to work.
After we delivered the '07 JK to American Expedition Vehicles, we began measuring the giant Cummins 24-valve, common-rail, 5.9L diesel engine and of course found it to be much larger than the factory '07 Jeep 3.8L V-6. The Cummins weighs around 1,100 pounds and is nearly 3 feet tall, 3 feet long, and 3 feet wide, so the project of stuffing that engine into the Jeep frame was going to be an uphill battle. However, the Jeep frame is no weenie frame as in olden days. In fact, its fully boxed chassis is made of tubing 2 3/8 inches wide by 5 1/4 inches tall-bigger than some 1/2-ton trucks we've seen. | 
Luckily we were able to get our hands on a complete rolling chassis for an '06 Dodge Mega cab that was headed for the crusher, and when we started measuring and examining the differences between the Jeep and the Dodge frame, we realized that the truck chassis could be shortened fairly easily. It already has big axles under it and all the proper mounts for the Cummins engine. Not to mention that this frame was engineered from the start for the torque the Cummins will produce. In the end we removed a 4-foot section of the 2 3/8 x 7 1/2 framerail from the center. | 
With the Dodge frame shortened down to the Jeep's 116-inch wheelbase, we could roll it under the Jeep body to determine where the engine would sit and what bodywork would need to be done. About now the AEV crew decided to move the engine back in the frame almost a foot. This helps keep a balanced weight front to rear, offers more space for a custom radiator, and keeps everything under the factory Jeep hood and behind the original grille. It also means new motor mounts and a proverbial butchering of the Jeep firewall. |
In fact a massive hole was cut in the firewall to make room for the engine, plus the entire heating and air conditioning system had to be removed, for good. Luckily Hobart is the official welder and plasma cutter of Ultimate Adventure so when the old shop plasma cutter started acting up, Hobart came through with one of its Airforce 625 plasma cutters to help in the removal of unwanted metal. The 625 can cut up to 1/2-inch steel so it should work great for everything on this job. About this time you're probably wondering why we were going through so much trouble, and actually so were we. But whenever we thought about how awesome a diesel-powered Jeep would be, not to mention one running a Cummins diesel from a 1-ton truck, we felt it was a good cause and a great project. Plus we knew you would all want to know if it could be done and we hate to disappoint.
Our next step was to rebuild the firewall around the engine with enough space for any movement of the Cummins on the engine bay side, while still having some semblance of foot room on the occupant side. This meant stuffing the engine in the frame and dropping the body down over it. As you can see, the engine is quickly entering the Jeep tub looking for a place to live. | 
As we continued to build out the firewall, we realized that the passenger's left foot and the hot exhaust from the turbo dump will be trying to occupy the same space. Even worse, on the driver side the throttle pedal and the Cummins starter were having domestic disputes about living in the same place. | 
We looked into different options for the starter and even borrowed an early '90s Cummins starter (bottom) from U.S. Diesel Parts in Missoula, Montana. We eventually determined that by rotating the '06 starter (top) around in its mounting hole we could get it out of the way for the throttle pedal. This did involve some custom welding to the Cummins engine adapter that the starter mounts to. |