The 177mph 1,400-HP Duramax Rocket

If you’ve ever looked at a full-size diesel truck flying down a dragstrip and thought “I wonder what that engine would do in something lighter,” you would not be alone. Diesel trucks are awesome all-around vehicles, but for all-out speed, their 6,000-8,000 lb weights hurt quite a bit. Brad Makinen thought diesel trucks were dang heavy too, so he decided to do something about it. In 2007, he debuted the “DirtyMax,” a tube chassis drag truck that he’d stuffed in a Duramax. Although the truck eventually ran mid-8s in the quarter mile, the 3,460-lb rig was on an outdated chassis and miles away from the 2,350-lb minimum of the Pro Stock Truck class.

“The complete rolling chassis and body with no engine or transmission comes in at around 1,200 pounds, which is darn crazy”

A couple years ago, Brad got tired of racing against lighter, newer rides and decided to build one for himself. Partnering up with MBRP Exhaust, Brad started his new build with a 1941 Willys Pro Mod body, and a 2001 6.0-second certified chassis, built by Tommy Mooney. The chassis itself is chromoly steel, and built with double-framerails, for maximum resistance against a diesel engine’s massive torque. It’s also very light, and we mean VERY. The complete rolling chassis and body with no engine or transmission comes in at around 1,200 pounds, which is darn crazy.

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The interior of Brad’s Willys is all business, which means light. Anything that isn’t tubing is made from carbon fiber, to keep weight down. Also visible is the Lenco CS1 transmission that handles the engine’s power and torque.

Did we mention the part about it being light? The race seat for the Willys isn’t so much a seat, but a few panels of carbon around the 6.0-certified rollcage.

The front suspension of the Willys is traditional drag car components, designed for going in a straight line. The struts and brakes are from Lamb, and the steering is a Flaming River rack and pinion. The entire front suspension and steering weighs barely over 50 pounds.

One place where strength can’t be sacrificed for weight is the rear axle, which will have to handle 40psi launches and 60-foot times in the 1.1-1.2 second range. A Mark Williams 9-inch rearend with a custom 2.91 gear ratio and 44 spline axles supplies the power-handling capabilities, while carbon fiber brakes from Strange keep everything light.

The Duramax engine was actually quite easy to mount in the chassis. The factory mid-plate could be used with the Lenco/Bruno drive, so just an engine plate had to be fabricated up to put the LBZ block-engine in the Willys chassis.

A small aluminum radiator is all that is needed for cooling. An equally small and light fuel tank is filled with the small amount of diesel that it takes to go a quarter mile at a time.

A FASS lift pump is mounted in front of the engine to combat the enormous G forces the car sees on the launch. From the FASS, fuel then feeds twin CP3 pumps from Exergy Engineering, one of which is mounted in the factory location, and the other where the water pump used to be.

Boost pressure is provided by twin Garrett GTX4094R turbochargers. The 67mm units are wastegated to 55psi, and are equivalent to a single turbo of more than 90mm in inducer size.

Masterpiece Dmax

So Brad had his new state of the art chassis, which just meant that he now needed a motor. Built with lessons learned from the DirtyMax, the 6.6L Duramax that powers the Willys is a masterpiece of engineering. Starting with a quarter-filled LBZ block, Brad stuffed the engine with Carrillo rods, Mahle pistons designed with bowls to Brad’s own specifications, and surprisingly, a factory LB7 crankshaft. Main stud bolts were upgraded with ARP studs, and the engine also received a set of trick ARP 625 head studs. The engine was mounted low in the chassis, practically on the ground thanks to a dry sump oil system from Pacific Performance Engineering.

The parts that make power are top notch as well. An experimental camshaft from Hamilton Cams actuates a set of titanium pushrods from Trick, before opening the valves of the Wagler Racing cylinder heads. Built as a joint venture with Brodix, the CNC ported heads flow a whole lot more than the factory versions, allowing for greater power at lower boost levels. Speaking of boost, for flow and packaging purposes, the Willys uses twin GTX4094 turbochargers, that are wastegated to 55psi of boost with twin 60mm Turbosmart wastegates. These turbos were mounted with a custom set of headers built in-house at G&J Diesel.

“Bosch Motorsports stand-alone ECU allows virtually limitless tuning possibilities, while enabling the engine to spin to a whopping 5,750rpm redline”

For fueling, the 6.6L in the Duramax makes a big departure from the norm by running a Bosch Motorsports stand-alone ECU. The Bosch ECU allows virtually limitless tuning possibilities, while enabling the engine to spin to a whopping 5,750rpm redline. Supporting the Bosch system is a 200gph FASS system, and twin CP3’s from Exergy Engineering. For injectors, Brad alternates between Dynomite Diesel units, and Exergy Engineering injectors. Tuning for the whole system is handled by Ryan Milliken from Hardway Performance.

“The Willys is within striking distance of the current Pro Stock record”

For ease of maintenance and to keep water pressure constant, an in-line electric pump is used on the Willys, rather than an engine-driven one.

The Garrett turbos are right at their limits at 55psi, and a blown boot can cause a turbo to overspeed and come apart. To prevent this, every connection is equipped with boots and straps to firmly secure the intake piping.

The 6.6L Duramax engine that’s mounted in the Willys is good for an estimated 1,000 rear-wheel horsepower (so far). The team hinted that there’s easily another 300 to 400hp left in it with additional tuning and more nitrous.

The Transmission

For weight and durability, another departure from the norm was made in the transmission department. Instead of an Allison, the Duramax is hooked to a three-speed Lenco, through a Bruno converter drive. The planetary gear transmission has virtually no lag between shifts, and even incorporates a lock-up converter built with help from SunCoast Converters and Precision Industries.

Nitrous oxide is used for both spooling the large parallel twin turbos, and also to add a little more oomph while heading down the track. Two 15 pound bottles send the gas to four solenoids, and four nozzles. So far the Willys has only been ran on four 0.022-inch jets, which is barely anything at all.

The crown atop of the Duramax engine is a Wagler Competition Products air-to-water intercooler intake. Designed to handle enormous boost pressures, the intercooler box ensures plenty of cool, dense air is sent into the engine.

Although the body is Willys-based, it’s been heavily altered for this fiberglass Pro Modified application. A large rear wing is molded into place, to help keep the rearend planted at speed.

Drag race-only wheels and tires are used, since the car only sees a quarter mile at a time. The front wheels are from American Racing, while the tires are super-skinny 25x5x15 Hoosier Drag Fronts.

Hoosier Tires are used in the rear as well, only this time, they’re enormous 34.5x17x16 drag slicks. They’re mounted on Weld Racing beadlock wheels that allow for very low tire pressures (below 10psi), for as much traction as possible.

Extremely long wheelie bars are a Pro Mod trick to provide lots of resistance against wheelstands, yet not upset the chassis on the launch. At nearly 180mph, stopping suddenly becomes very important. In addition to the trick braking system, twin Stroud parachutes are used to slow the car from hyperspeed.

Early Results

At a 2,600-2,700lb race weight, the Willys has run a best pass of 8.28 at an astounding 177mph and is getting faster every pass. Currently at around 1,000rwhp, the team has another 300-400hp left on the table, which means the Willys is definitely within striking distance of the current Pro Stock record. With a stratospheric redline, unique transmission, and powerful Duramax engine, Brad’s newest ride has come out of the gate storming! DW

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Pinaki Bhattacharya

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