Heart of the beast is a type M-11 diesel engine that put out staggering torque at ultra-low rpm.











Mike Lund and Marty Sigfried were given the driving chores.











Practice sessions in the Mojave desert revealed a top speed of over 110 miles per hour.











Minds were blown when The Big Mule roared off the line at the Baja 1000.











Construction took over half a year at the T-Mag shop.











Serious loading ramps were required to get the big semi up on the flat bed.











Oddly enough, the semi was not top-heavy, even with the long travel suspension.











A custom painted International Eagle was prepped to haul the racing semi.











Here’s what El Burro Grande looked like before it was made into an off-road racer.

Bill Savage (owner of T-Mag) was given the job of turning a Cummins semi into an off-road racer. The idea was the brain-child of a joint effort between Cummins and Navistar. Cummins wanted to promote the reliability of their new M-11 engine, and Navistar is a moving force behind the growing Global Positioning technology.

UNDER THE HOOD

What's the fuss about a diesel engine? Study the spec sheets and check out these numbers: The single turbo-charged, inter-cooled, diesel powerplant puts out 370 horsepower … at 2200 rpm!

But here's the real stunner! It twists out a whopping 1350 ft/lbs of torque at a mere 1200 rpm! At a point of about 400 rpm higher than most engines idle, the Cummins M-11 puts out 1350 foot/pounds of stump-pulling torque!!! Compression ratio is right at 27:1.

This is not a small motor, by any means. When put on the scales, the engine/transmission package weighed in at a whopping 3000 pounds!

THE DRIVE TRAIN

The stout powerplant is hooked up to an Allison 6-speed automatic transmission. Stall-speed on the torque convertor? A mere 800 rpm! Another amazing fact is that the trans/torque convertor in the racing Cummins is totally 100 percent stock. They chose to run it that way to demonstrate the reliability of the unit.

Instead of the regular cooler for a trans, the Allison uses a true heat exchanger. Shifting is done electrically and this set-up is also Allison-based technology. Just in case you wondered, they had no trouble at all with the stock trans.

A Dana/Spicer diff is used at the rear, running a 3.80 ratio. It's from the Diamond Series, which is a normal 5-ton item regularly found in larger box vans. If you want one, the part number is S-150-5.

BUILDING IT!

Bill chose not to use the stock frame as a base, but because of SCORE rules and regulations, would have to conform the racer to a 9200 Cummins body style, and stick to the 152 inch wheelbase, plus or minus a few inches.

A tubular frame was hand made from chromoly steel tubing (1 3/4" OD by .120" wall thickness), and complete construction of the frame and running gear took six solid months of work!

Up front, Bill made a twin-beam concept front end similar to a Ford. At the rear, a standard 4-bar link was used. Since the Cummins was huge to start with, Savage could have literally built in as much travel as he wanted, but instead, chose to keep it conservative. You can find 22 inches of travel up front and 28 inches at the rear.

At first, it was feared that the finished package would be too tall and top heavy, leading to flop-overs in rough off-road racing conditions. Since the Cummins taped in at 9 1/2 feet tall, they had a right to be concerned. But once out in the field, they found that flop-over was a non-issue and that the semi was amazingly stable.

FACTS AND FIGURES

• The Cummins carried 160 gallons of regular old pump diesel fuel in two separate 80 gallon fuel cells. It was estimated during testing that they would get six to seven miles per gallon under normal race conditions, meaning they could run the entire Baja event without refueling.
• Coil-over air shocks were used at the front and regular hydraulic shocks used at the rear. Two shocks per wheel seemed to be right during testing, but on race day, it was not quite enough.
• Hefty heim joints were used at all pivots; most of then were 7/8 inch bore aircraft quality stuff.
• Wheels are aluminum slugs from Alcoa: they're 22.5 x 7 items. The Goodyear tires are 42 inches tall and are labeled 385/65/x22.5 Super Single 8 plies. Each tire weighed 180 pounds and a complete tire/wheel assembly hit the scales at a whopping 260 pounds! Tire pressure was run at 40 p.s.i., which must have been a savvy guess, since they had no flats or wheel problems in the race.

This was good, since a tire change would have been equivalent to any Olympic-level workout. A jack was built into each side of the semi, just in case.

• Modine radiators (brass, not aluminum) were used. The front ran an electric EFE 24 inch fan for cooling and the rear used an hydraulic drive fan that ran off a remote power steering type pump.
• Steering chores on the big rig were handled by a Tommy Lee Saginaw box. Custom tie-rods and pitman arms were fabricated from hefty chrome-moly tubing.
• To keep dirt out of the powerful engine, Cummins used a heavy duty element filter from Fleet-Guard. Bill Savage reported that not only did the filter do an excellent job keeping the dirt out, it was unaffected by rain and splashing water. Bill noted that he would not hesitate to use this type of filter on a regular race vehicle.
• That slick looking cab is fiberglass; molds were taken off the stock steel parts. All that trick work was done by Vec-Pro, a custom glass shop in Anaheim, California. The great looking paint job was applied by Bill Bushling, who can be reached only through T-Mag.
• Important details: Seats by Mastercraft, lights by PIAA, belts from Simpson, gauges by Autometer. That whopping big skid plate up front was fabricated from T-6 aluminum alloy by Bill Savage, as was the wrap-around front bumper. The engine electrics are stock Cummins stuff and they worked just fine.
• The all-up ready-to-race weight of the Cummins race semi was a touch over 9,000 pounds. Since a stock Cummins cab weighs 11,500 pounds, it's obvious that Savage managed to save a bunch of weight.

HOW DID IT WORK?

Rather than string you out, we'll tell you up front that the Cummins racing semi retired from the event at the 300 mile mark. They had shock problems due to incorrect valving, which led to harsh forces on the shock mounts and some mount breakage.

Shocks were replaced, but the spares were valved wrong, too. After the team ran out of shocks, the semi was driven back under its own power to a pit and put on the trailer.

But when it ran, it ran great! Bill, who spent some time behind the wheel during testing, said it was surprisingly quick. Top speed, measured on a dry lake bed, was over 110 miles per-hour!

Bill noted that there was so much torque, that they never needed to use the bottom two gears. Acceleration, he said, was faster than a good Class 7S truck.

Mike Lund, a long-time veteran driver, was chosen to pilot the big rig, and the plan was to drive quick, but not hard.

All three chase trucks were equipped with GPS, and at any time they could check the following things on the race truck, by glancing at the read-outs: mile-per-hour, engine rpm, all engine temperatures, turbo boost pressure, shock temps, rear end temps and tranny temperatures.

The drivers said that the driving position let them see "forever" sitting that high up in the air. The only draw back was that tree branches kept filling up the cab. Oddly enough, a low hanging tree branch wasted the front fan and the engine ran hot for a short while until the fan was replaced.

Everyone connected with the project mentioned that the huge truck handled extremely well, and the long travel suspension really handled the bumps.

WAS IT WORTH IT?

Sure. It cost a cool half-million dollars to complete the Cummins racing semi, but Cummins/Navistar were happy with the positive publicity. Even better, they felt that the new M-11 engine was more than capable of handling anything that could be thrown at it,

The Big Mule has been retired, and is put on display every now and then. It’s gone, but certainly not forgotten. Just ask those who saw the big beast run!