Everything, it seems, in Chaz Lightner's life is orange and black. That includes his T-shirt, his business card, and his '66 Bronco, which makes black smoke when he gets on the throttle. Color aside, the Bronco is many things rolled into one — solidly built trail machine, daily driver, fuel-efficient commuter, and turbocharged, intercooled, high-torque stoplight-to-stoplight surpriser. But most of all, it's a unique 20-year-long engineering project, a rare 4x4 combined with a rare engine, the 4BTCummins diesel.
Chaz has long had racing in his blood, so this particular Bronco has a history, having been fitted with a number of high-performance gas engines, including a Can Am Ford 408ci V8 built to the tune of 520 hp. Radical turbocharging provided huge horsepower numbers, but turned out to be somewhat less driveable than Chaz had in mind, so he came up with the idea of using a Cummins diesel to provide big torque in a more progressive, efficient manner. The more familiar 5.9L Cummins B6, used in Dodge Ram pickups among other things, is a long son-of-a-gun - practically impossible to fit under the hood of an early Bronco. And it's heavy - too much for most front springs - and nothing lightweight can live behind it for long.
The Cummins 4BT four-cylinder, the baby brother to the 6BT, isn't exactly light either, but it would prove to be feasible to swap. From the factory, the 4BT is usually rated at 105 hp and 265 lb-ft of torque, but they can be built to much higher specs. With a simple turn of the screwdriver, a 4BT can make over 160 hp, and over 400 lb-ft of torque. With more fuel, a turbo and intercooler….the sky's the limit. Plus, while the motors are somewhat scarce, a 4BT still costs much less than a 6BT and many can be found languishing in late 1980s bread vans, which were converted to diesel by Cummins in the mid 1980s. The aged vans, engine and all, can often be had for under $3,000.
To recondition the engine, Chaz went to Beck Racing Engines in Phoenix, Arizona, where it was rebuilt, balanced, and blueprinted to keep noise and vibration to a minimum. Since the engine would be operating under heavy boost, the head was fire-ringed and the head bolts were replaced with 14mm ARP studs. The fuel delivery system was upgraded by combining a lift pump from a 12-valve Cummins and a four-cylinder P7100 pump. It was designed by Ken Diaz at Turbo Auto Diesel, who also added 125 hp Cummins injectors.
Finding the right turbo took some experimentation. The first setup was too large by far, kicking in with 88 psi at 3,000 rpm. "It was crazy," says Chaz. Eventually, by matching up various shells, centers, and exhaust housings, Ken came up with a turbo that kicks in at 1,800 rpm and builds boost to a maximum of 57 psi. Given the current setup, the Bronco will cruise at 65 mph at about 6 to 7 psi of boost, allowing for 25 mpg, or better.
As you might imagine, fitting the engine and plumbing required extensive custom work. Assisted by friend Matt Bong, Chaz got the engine situated after numerous trial fits. Chaz made the motor mounts himself, employing inserts from Energy Suspension, and welded up his own aluminum radiator using pieces of aluminum sheet. The 4BT is short enough to fit with plenty of room for the radiator, but still required notching the frame to give the Cummins starter clearance, and to clear the NV4500 transmission. A 1-inch body lift helped make working clearance as well.
However, it wasn't a huge surprise that Chaz quickly found the original NV4500 couldn't stand up to the torque, in part because he could only fit the bell housing intended for car applications. As a result, the largest clutch he could run was 10 inches and he burned out three of them before deciding something must be done. Fixing the problem is a Sun Coast 4R100. The Sun Coast unit employs a variety of upgrades to the hydraulics and the clutch pack, and features a Mag-Hytec deep pan. Scott at Destroked.com machined the adapter to mate the transmission to the 4BT. It took a while to get the automatic dialed in, and some programming help from expert Nate at Strictly Diesel, but now it shifts smooth and clean, and the torque converter locks up at five mph. Ironically, notching the frame would not have been necessary had the 4R100 been installed in the first place.
With all that boost and fuel, high exhaust gas temps could become an issue, so Chaz worked with Vortech Engineering to build a custom air-to-water intercooler. The system uses the A/C compressor mounted on the engine to chill water for the intercooler, which does its job by cutting the intake air temperature 50 percent.
The Sun Coast automatic puts power to the ground through a 4.3:1 Atlas II transfer case. The front Dana 44 is enhanced with Currie shafts and Warn outers, and an ARB Air Locker for those moments when both ends have to be locked. The rear axle is a Currie 9-inch with 35-spline shafts and an Eaton Performance Detroit Locker. Both axles house 4.56 gears from Currie. The front end is lifted 3.5 inches via Wild Horses coil springs, and the rear is lifted a like amount using carefully-made 12-leaf Wild Horse spring packs. All four corners are double shocked with Rancho RS 9000 shocks.
The suspension is soft enough for trail work and everyday driving, but not too soft to go around a corner on the street with the 9000s set on 5. With this setup, Chaz has the lift, the ready torque, and the gearing to turn 35-inch BFGs on Eagle 589 wheels. Just in case, a Warn XD9000i sits up front.
The interior is contained by a full roll cage and sheltered by a brief soft top. The custom dash is fitted with the usual instruments - water temp, oil pressure, voltmeter, fuel level and fuel pressure - plus a few others you'd like to have with a diesel, including boost pressure and exhaust gas temp (EGT). Overhead is an array of switches that control ignition, wiper motors, an electric cooling fan, and auxiliary driving lights. Twin Beard seats with four-point Simpson racing harness help secure driver and passenger in the event of a rollover.
Chaz's Bronco is loaded with thoughtful custom touches. The tailpipe is routed to the side, exiting through the right rear quarter panel. All essential equipment is securely mounted and ship-shape. That includes the Hi-Lift jack, which is mounted along the side of the rear bed in a secure and accessible location. There's a compact air supply bottle near the tailgate to air up after trail rides. Also at the rear, tucked to the side of the rear seat, is the aluminum cooling tank, shaped to take maximum advantage of the hump over the wheelwell.
Chaz has been working on his Bronco since he bought it for $300 in 1984, and he's not done yet. But for the time being, he's enjoying a reliable 400 hp, diesel-powered Bronco that gets 25-plus mpg, "as long as you keep the boost under 10 psi and engine under 2,000 rpm." He can run pump diesel mixed with biodiesel or practically anything else in a 50/50 ratio and, in the warm weather of Phoenix, has no problems with fuel flow.