A Bimmer in Baja

“The best thing about building and racing a car of your own concept” says Martin Christensen, “is the sense of satisfaction you get when you win…doing something better than anyone else with your own ideas.”

Martin Christensen runs the only BMW-powered single seater in the SCORE desert racing series of six major events per year in the American Southwest and Mexico. “Most people are accustomed to thinking of BMW power in a Formula One car, a Le Mans prototype or a championship GT car,” he says, “so they’re surprised when they see a BMW engine in a desert racer. But that’s why it’s so good-it has a real racing heritage.”

If a BMW engine makes a somewhat unlikely powerplant in a desert racer, Christensen himself makes an equally unlikely pilot. A native of Denmark, Christensen came to Southern California 12 years ago at the age of 21, shortly after completing a stringent course in mechanical engineering and auto mechanics at Denmark’s national technical institute. He came to California to join his older brother, Hans, who had started Escondido independent repair shop All German Auto several years earlier. “We specialize in BMWs,” Christensen says. “I love these engines-that’s why I run one in my race car!”

Back in Denmark, Christensen’s father had a garage that prepared a few rally racers, which fired Martin’s interest in racing. “Scandinavians are mad about rally racing; in Denmark we have a lot of dirt roads so you grow up learning car control at an early age.” He says with a grin. Soon after he arrived in America, Christensen discovered he was living at the epicenter of Southern California’s thriving desert racing community and that SCORE’s events, surprisingly, held much in common with the races he’d attended back home.

“We don’t often have snow in the desert,” he laughs, “but the competition is better than anything we had in Europe.” Better than the World Rally Championship events? “Yes; those cars run on ‘special stages’ that are much shorter and considerably smoother than the roads we use here. As powerful and fast as they are, those factory rally cars couldn’t begin to compete against us in the desert. Our cars are far more specialized,” he asserts, pointing to his spidery, open-wheeled single-seater, “and the top desert cars are much faster. This is really the most exciting form of racing in the world!”

At first, Christensen couldn’t afford to race a car, so he reverted to his beloved dirt bikes (he’d been riding since age 8 and had won the Danish Junior MX championship at 11). By 1996, he’d learned enough about the demanding terrain in Mexico’s famed Baja California peninsula to win the 250cc class in the legendary SCORE Baja 1000.

Christensen explains that SCORE’s history goes back more than thirty years, starting with the famed 1,000-miler through the mysterious and challenging Mexican outback. Over time, that classic event has evolved into the one of the best road-racing series in the world. Although he’s thoroughly familiar with conventional SCCA sports car competition through the prep work he     on some of his customers’ cars, Christensen much prefers the challenge of long-distance racing on dirt roads. “It’s a great series for privateers and professionals,” he says, “because you can begin at the simplest level and work your way up, and driving skill counts for more than money.”

And that is just what Christensen has done. After his success on the bike, he was determined to build and race his own car. The growth of All German Auto allowed his to build a Class 9 VW-powered racer, and he won that championship in ’98. That fired his ambition to build his current BMW-powered Class 10 car, although his goal, if he can find the backing, is to design and build his own Class 1 “Unlimited” racer powered by a BMW V8! “Some day, I want to win the 1000 overall,” he says passionately. “That’s the big one!”

A more intense form of rallying, perhaps?

It’s a big one, though, that has remained largely invisible to those outside the loop. “If you don’t live in the Southwest,” Christensen continues, “it’s hard to understand our type of racing, because there is comparatively little interest from the national press.” Televised coverage, except for the Baja 1000 each fall, is pretty sporadic. Because of the remote locations and difficult terrain, a television crew has to rely on helicopters to cover an event, which can drive the cost up more than five times as much to cover a conventional pavement race.

“The logistics, just like running a car down there, are complex and expensive,” he continues. “Our racing is very popular but, just like rallying in Europe, you have to be a serious fan to spectate.” But that doesn’t mean the SCORE series doesn’t have its fans. There are literally thousands of spectators along the roads at the biggest events, and that’s not just because the races are free; the SCORE series fans come because the action is far more exciting than anything, anywhere on pavement and you can watch from as close as you dare! You can take your SUV way back into the remotest part of Baja, camp out for a couple of days, and watch the racers come through some of the wildest and most beautiful terrain in the world.

It’s also a form of racing that appeals to the purist on a level which no closed-course competition really can. Although it’s usually referred to as off-road racing, it really isn’t, because the desert races are actually run on the old dirt roads that cover much of the backcountry in Baja California, Nevada and Arizona. And in format, SCORE races resemble auto racing from a bygone era; the cars (often more than 200 starters) are flagged off at 30-second intervals, by class, and are timed based on their starting position. “If you’ve ever seen old photos from the 1920s,” Christensen says, “of the Targa Florio in Sicily or the Mille trucks, but in reality are full-race, tube-framed silhouette racers. What makes these two categories so interesting is the lack of rules. Other than required safety equipment, almost anything goes. That means racing’s top designers, fabricators and engine builders have a free hand to invent and innovate, so the results are astoundingly interesting compared to conventional cars designed for pavement.

Aerodynamic downforce, the bane of modern racing, is almost nonexistent. Suspension travel is measured in feet instead of thousandths of an inch. Some Trophy Trucks have well over 36 inches of wheel travel and the shocks-some as big around as your thigh-are hand-built, state-of-the-art units that almost defy description. Their complex internal bypass systems (some are even water-cooled) must work effectively on faster smooth sections, at speeds over 130 mph, as well as in the roughest terrain, where every inch of controlled suspension travel is a bonus.

Christensen competes in Class 10, SCORE’s third most popular class. His mid-engined, single-seater might be compared to a 675 LMP Le Mans racer, as
BMWs breathe better, and that can be a problem!

Class 10s are the most technologically advanced “lightweights” in desert racing. They are almost identical to the fierce Class 1 “Unlimiteds” with the exception of their smaller engines. They are required to run easily available, production-derived engines, limited to 1,650cc displacement. A competitor can start with a larger or smaller displacement engine and modify it internally any way he wants as long as it meets the 1,650cc rule. All engines must be equipped with the car’s original intake manifold and induction system (which cannot be ported more than a quarter of an inch inward from the mounting flange surface). This very practical breathing limitation, like the intake restrictors found in the ALMS, is what keeps all the marques in Class 10 on a comparatively equal power basis.
Christensen’s M42 engine came out of a ’91 E30 318is and had to be destroked from its original 1,800cc to meet the class rules. “That gives the engine exceptionally good breathing without having to do a lot of special headwork, with larger valves,” he explains. SCORE’s racer-friendly rules are Miglia, you’ll know instantly what I’m talking about. This is real road racing.”

In Mexico, the competition is held on open roads, complete with daily traffic, unfenced farm animals and spectators lining the edge of the course for miles. What’s even more impressive with today’s technologies are the speeds. These modern desert racers cover ground at an astonishing rate; much, much faster than the early Grand Prix Maseratis, Fiats or Lancias seen in those yellowed photos of early racing history.

Desert racing has three top classes, of which the two quickest are the technologically opposed Class 1 “Unlimiteds” and the huge, powerful “Trophy Trucks” that vaguely resemble production pickup opposed to a 900 LMP, which would be the equivalent of a Class 1 “Unlimited.” The car’s chassis, built by Jimco in El Cajon, CA, is made entirely of chrome-moly steel tubing that is left unpainted so it can be inspected for cracks and repaired in the field, if necessary. The level of fabrication matches the best anywhere in the world. All the exterior panels can be quickly removed using Dzus fasteners, so maintenance is fast and easy instead of a hassle designed to make them easily enforced, and post-race tech inspections rarely last more than a few minutes. Injector throttle bodies in Class 10 are limited to 58.5mm in diameter, a size empirically determined by those found on the class’ most popular engine, the twin-cammed Honda Accord.

Christensen’s BMW-engined Jimco caused a furor among the other Class 10 competitors when it first appeared, as it smoked them wherever horsepower was an advantage. The BMW’s stock throttle body is a unique dual-port design that has a smaller primary for good low-end throttle response. The extra area of the smaller secondary port gave the BMW’s throttle body an area equal to 62mm, which naturally gave it a breathing advantage. SCORE’s Technical Director, Bill Savage, soon mandated the use of a Honda unit on the BMW’s manifold to restrict its breathing. The only way Christensen could mount the Honda component on the BMW is to position it at 90 to the stock unit. That caused the butterfly to operate vertically instead of horizontally, which in turn destroyed the even fuel distribution of the stock BMW unit.

Once that fuel-distribution problem was discovered, Savage allowed Christensen to revert to the BMW throttle body, albeit with a sleeve in the primary port so the total area of both ports matched the smaller Honda unit. The M42 again delivered a smoother power curve all the way to the engine’s max 9,500-rpm limit. “When I first installed the BMW engine, it delivered just 106 hp to the rear wheels,” says Christensen, “considerably less than the Hondas, VWs and Toyotas were getting. They were easily passing me on the straights, but with a year’s careful development at SD Engines in San Diego, we’re now getting 195!”
Christensen also does some special engine development and machine work with Meziere Enterprises, close by in Escondido, but he prefers to use a chassis dyno to test horsepower figures because chassis setup and rear axle angularity can severely affect the final power figures. “I want to know exactly what I’m getting at the wheels, not the engine,” he explains. “If we want to run our maximum ground clearance of 18 inches, so we can take full advantage of the suspension, the CV joints would run at maximum angularity and that really absorbs too much power, so we set the car’s ride height up for each race, according to the type of terrain we’ll race on.” He then tests his engine on the chassis dyno at race ride height.

Chassis R&D, and a hotline to Bilstein

Because the terrain can vary so much in a desert race, the ability to tune the chassis for different conditions takes on a completely different meaning that it does for a car designed to run on pavement. When Jimco takes an order for a new chassis, it will make any custom modifications to its several basic designs to suit a competitor’s desires. Since a variety of engines and transaxle options are available, wheelbase and track can be adjusted to suit a driver’s preference, as well as cooling system placement and weight distribution. Initially, Christensen’s mechanical engineering instincts told him to pursue a radical beltdrive system of his own design (to eliminate the use of CV joints) but a season’s frustrating results with rapidly deteriorating belts (because of foreign matter intrusion) caused him to revert to a more conventional independent rear suspension system.

“Nothing is ideal in this sport. The beltdrive concept is still valid, but I had to decide whether I wanted to be an R&D shop or run a winning car.” Like most racers he’s always looking for an edge but sticks pretty closely to what’s proven. “You have to know you can finish to win.”

Christensen’s mid-engined chassis is one of the best handling in the series, and watching it negotiate rough terrain at speed is a wonder. All four wheels pump up and down at a furious rate but the driver’s cell remains in a relatively smooth position above the ground. His car is also one of the best at staying hooked up, with a minimum of wheelspin as the engine puts power to the ground. Christensen credits his custom-built Bilstein shocks, which cost about $10,000 dollars for the set, “but worth every penny!” Because of his front-running status, Bilstein also provides Christensen with complete tech support, rebuilding and recalibrating the dampers for every race.

“Shock technology in the desert is far beyond anything we’re used to in production cars,” he says. “I work closely with the Bilstein established this facility just to work with the desert racers, because they knew more could be learned in the desert (for future use on production vehicles) than in almost any other type of racing.”

The chassis has to work on the fast, relatively smooth desert roads, as well as the rougher sections of the course. There might be miles of sand-filled “whoops” or even boulder-filled canyons where speeds of more than 20 miles per hour might be difficult to maintain. One shock setting can’t work for every terrain, as wheel travel in the rougher areas requires a completely different set of applications. The unique (and complicated) triple-bypass systems integrated into these custom-built shock bodies allow the piston within the shock housing to dampen movement and speeds differently depending on where it rides internally-very trick.

The five-speed transmission in Christensen’s Jimco is a specially built Fortin unit designed and built in Southern California just for desert racing. Many of the internal components are English, from Hewland, and made to the highest standard. Limited-slip devices are seldom integrated into these units, because desert racing cars spend so much time in the air-practical experience has shown that an LSD unit can knock the car violently off line when it returns to earth. Instead an aluminum “spool” locked rear end is used, as its rugged practically has proven reliable and predictable. The ring and pinion is a 4.86, which gives the car a top speed of 108 mph at about 8,300 rpm in fifth gear.

Christensen uses BF Goodrich tires on all four corners. “I ran another, lighter brand with great results on my Class 9 car,” he says, “but the higher speed of this car demands the strongest casing available. These Baja T/As are heavier than I’d like, at 62 lbs. including the wheel, but they’re as tough as they come.” The difference in speed between his previous Class 9 car and the BMW racer is extraordinary, he says. “With the higher speed, there’s comparatively little time left to read terrain, so you tend to make more mistakes. The tires have to be able to take the abuse.”

The purest form of racing

Desert racers are pure function, but every aspect is designed from a practical aesthetic that has its own raw beauty. There is no “perfect design” for this type of racing, only integrated performance-enhancing concepts which may or may not prove advantageous on each course. And, since the courses change from year to year, no particular design will ever have a distinct advantage. Craggy mountain passes over boulder-strewn roads demand incredibly rugged construction, just as flat-out runs over silt-ringed dry lake beds require a completely different design advantage.

“Nothing ever remains the same, and it can even change dramatically with the weather,” says Christensen. “A winning car has to be able to do everything well…and you have to have a dedicated crew that will go anywhere to keep you running. It isn’t easy.” But it’s a great challenge, and a good crew is just as important in the desert as a great car/driver combination. Christensen teams with longtime racing partner Charlie Hovey, who runs a Class 1 car. “We have about 40 people down here on a race weekend to service both cars,” he says. “Most are volunteers, but 10 are full-time mechanics, some of whom work with me at All German Auto. We also run two specially prepped 4WD chase trucks and ten pit vans that carry enough spares to rebuild anything on course. It’s a great team.”

All racing is expensive, but it’s far less costly to run a competitive desert race than almost any form of pavement car. “And the time you spend in actual competition on any given weekend far exceeds what you get at an SCCA event. Try running several hundred miles and desert in less than 24 hours, continuous except for pit stops, the way we do in the 1000…then you’ll really appreciate what it takes to be a desert racer, and why it’s such a challenge for the entire team.”

It’s taken him a couple of seasons to learn how to get the best out of the Jimco chassis and Bimmer engine, but Christensen’s car now seems on equal terms with the fastest Toyotas and Hondas in his class. “At first it was very difficult, because no one else had any experience with BMWs; I had to do everything on my own. Research and development with no factory backing is expensive.” He grimaces, thinking of all the money he has put into the car and engine, but then smiles when he describes coming off a particularly difficult corner and blowing by his toughest competition! “That’s what it’s all about. I love these BMW engines!”