Engineers and technicians at Rahal, Letterman, Lanigan Racing have spent the last six months or more at their headquarters just outside of Columbus, Ohio, turning a pair of factory-fresh M3s into GT road racers for this season’s American Le Mans Racing Series (ALMS). And they have some big shoes to fill, considering the M3s the Rahal-BMW partnership ran last year won the ALMS GT championship.
The RLL Team starts, like all ALMS competitors, with a highly capable GT car. For the RRL team, that means a pair of 3 Series BMW that has already been upgraded by the company’s Motorsport or M division. (The M division is analogous to AMG at Mercedes-Benz, SVT at Ford, and SRT at Chrysler — subsidiaries that soup up the parent company’s cars and trucks, often for racing.)
The stock M3 carries a 414-hp V8 and a chassis with good handling qualities. BMW engineers in Munich then upgrade the engine for racing, knowing full well that ALMS officials will put restrictors on the M3s’ air intakes to limit their speed, an effort to make ALMS car competitive with each other. So engineers in Germany adjust the size of the ports, camshaft profiles, and compression ratios to get the most power out of the engine with the limited amount of air coming through the restrictors.
“The team in Germany compensates for the air-intake restriction by using variable-cam timing to overlap between intake and exhaust cams to get more midrange torque but still generate top-end power,” says Jay O’Connell, technical director at Rahal, Letterman, Lanigan Racing. “All of this lets the German team coax about 485 hp out of the engine.”
He notes that trackside testing at ALMS races makes it difficult to weasel around the air-intake limitations because after each qualifying lap and race, officials have each team start their engines, then they close the restrictors with two rubber plugs. “If the engine doesn’t stall within a given time, then they know there’s a leak in the air lines and they’ll disqualify you,” says O’Connell.
The BMW engineers, as well as the Rahal Team, are limited in what materials they can use in the engine. For instance, titanium can only be used in the rods, exhaust valves, and some of the retainers. And the engine block must be same as that used in the stock vehicle. “ALMS officials are trying to limit engine development to reasonable levels, keeping them stock engines that have been mildly modified,” says O’Connell.
BMW engineers also trimmed weight by exchanging many of the regular steel body panels for carbon-reinforced plastic (CRP) versions. The Germans also apply techniques once reserved for Formula One racers, including computational-fluid-dynamics and wind-tunnel analysis, to smooth out the car’s aerodynamics. And they switched the traditional relays and fuses for a pair of CAN buses and a Power400 controller, cutting weight while improving reliability and simplifying maintenance.
German engineers spend a lot of time fine-tuning the chassis and suspension. For example, they give the front wheels more caster so the car has more negative camber on the outside wheel in turns. This boosts front-end grip. They also increase the wheel camber.
“It runs about –3° to improve grip, compared to –0.75° for the regular M3,” says O’Connell. “Our geometry is set up to compensate for roll more so than on the stock car. And we keep the wheel camber angled more favorable for grip than on the street car.”
Front track, as measured between the centers of the front tires, is 33 mm wider than the stock BMWs. The racing tires are also 89-mm wider. “But even the 33 mm is enough to reduce the weight transfer, which gives more cornering grip,” note O’Connell.
German engineers swap a solid stabilizer bar for a tubular version. “Most street cars use solid bars because they’re less expensive and do the job,” explains O’Connell.” But the tubular versions are lighter, therefore more efficient, but also more expensive. And we go up in bar size to get more roll stiffness, so going tubular makes sense in that they keep weight down. Strength is really not an issue.”
Many of the changes and modifications made to the M3 and other ALMS cars eventually filter down to the automakers’ consumer lineup, one of the benefits automakers realize from participating in racing. For example, racing teams have long strived for a 50/50 weight distribution between the front and rear wheels. This balances the work done by the front and rear wheels and improves cornering. Street cars are now designed with that in mind as well.
And traction control, originally used to put power down on the race track, has also migrated to consumer vehicles. A more-recent example of technology transfer, according to O’Connell, is the CRP roof panel. “We use it for weight reduction and to lower the race car’s center of gravity, which makes for less weight transfer in the turns and more stability. Now street versions carry them.”
Rahal Racing’s efforts
Once the RLL Team gets its hands on the M3, it begins tackling hundreds of small items. For example, the wiring harness is trimmed to match the race car’s needs. Extra jacks and pigtails are removed or moved to where they are needed. The connection for the air-conditioner compressor, an ALMS requirement to keep drivers cool in the semienclosed cockpit during the summer, is in the rear rather than the front. This gives better weight distribution for racing.
The team spends a lot of time tweaking the suspensions, getting the car to handle well and drive fast. They also tailor the suspension to suit the individual drivers. A key part of this effort is the data-acquisition hardware and software from Pi Research, Indianapolis. It networks to sensors mounted in the car. The system then measures, records, and displays in real time, the pressures and temperatures of the fuel, oil, and tires, as well as several engine parameters. The DAQ system also records g-forces, speeds, weight loads, and gear selection in the transmission. The data gathered helps the team determine how changes made to the car affect handling and performance. The team even uses DAQ during races for up-to-the-minute information.
There are also changes that depend on the particulars of the race at hand. The first and last races of the season, for example, are longer than the rest — 10 and 12 hr rather than a little under three. For those longer events, the RLL team puts beefed-up brakes on the car. “We use heavier rotors with a different array of cooling slots and thicker brake pads,” says O’Connell. “In the shorter races, we can get away with lighter, simpler brakes, and it lets us reduce the amount of rotating unsprung weight. But in those longer races, brake components are exposed to thousands of temperature-fatigue cycles and we need more steel in the rotors to keep them from cracking.”
Durability is an issue with all the components and subsystems on the car. O’Connell’s rule of thumb is that every mile on the race track is equivalent to 50 miles driven by a typical consumer. “So when we run 12 hours at Sebring and do 1,200 miles, that’s the same as 60,000 customer miles in a 12-hour period. That’s a lot of wear and tear on the car.”
Another subsystem that gets altered to suit the track is the transmission. ALMS versions of the M3 use a transaxle as opposed to a traditional transmission to get the right weight distribution. “But we do change the gear ratios, replacing the gear stack, a job that takes about 30 minutes,” says O’Connell. “We don’t do it during a race. But in the days building up to the race, we try a couple out to see what works best. We use predictive modeling to pick our gears ahead of time, and the forecast is usually pretty close.”
But top speeds possible on the track can change because of changes in the wind or track conditions. Or a driver might find he’s running out of gear between turns three and four. So he may ask the mechanics to give him the next higher gear to save a shift and get around the track faster.
“Winning really ends up depending on a lot of small details, says O’Connell. “For example, we work hard with the drivers to get the cars as well balanced as possible, to get the most out of the package by optimizing the tires and set up for the track. For instance, we try to get the tires up to temperature fast so they have more grip and our first and second laps are faster.”
He points out that Le Mans race teams in Europe are allowed to use a tire-heating device, basically a kerosene heater and tent. In ALMS, teams don’t have that option. “We can only use the sun,” says O’Connell. But for that first lap, we might adjust the suspension, maybe add more damping, so tires heat up more quickly — whatever we can do to get an advantage while always staying within the rules.”
The same goes for the pit stops. “We work hard on our refueling routine and hardware system to minimize losses and put 110 liters of fuel in the tank as quickly as possible,” O’Connell explains. “Using suction is illegal. We have to rely only on gravity. But we ensure the flow path is as straight as possible, with the least amount of losses.”
“All in all, it’s been a lot off fun for us to get these latest versions of the BMW M3 on the track,” O’Connell says. “And as an engineer, it’s great to be part of the competition.”
A quick look at ALMS and the cars
American Le Mans Series racing includes four classes of cars, all on the track at the same time. This makes for lots of passing and race-track action over the course of the timed races. Winners are those that complete the most laps in the designated time. There are nine races in the season, starting with a 12-hr race at Sebring and ending with the 10-hr or 1,000-mile competition at Road Atlanta. Most of the seven races in between are limited to 2 hr, 45 min.
The four classes of vehicle are:
Le Mans Prototypes: Purpose-built racing cars with 600 to 700 hp. They weigh at least 1,980 lb, can go from 0 to 100 mph in 3 sec, and have top speeds over 200 mph. The field includes a pair of diesels, the Audi R15 and Peugeot 908 HDi, and the conventionally fueled HPD ARX-01c, Porsche RS Spyder, Ginetta-Zytek 09S and 09HS (hybrid), Lola (both open and closed-top coupes) and Creation CA09. LMP cars carry blue leader lights and car numbers for quick identification. (The lead car in each class has one light illuminated on each side of the car; the second-place car has two; and the third-place car has three.)
Le Mans Prototype Challenge: In this class, added last year, race teams all use the same type of vehicle, the Oreca-Courage FLM09 prototype. The 430-hp cars must weigh at least 1,980 lb, without driver or fuel. LMPC cars sport red markings on their rear-wing endplates, mirrors and roll hoops, and red leader lights.
Grand Touring: Cars must be production-based, moderately modified two-wheel-drive vehicles. They include the BMW M3, Corvette C6.R, Ferrari F430 GT, Ford GT-R, Jaguar XKRS, Panoz Abruzzi, and Porsche 911 GT3 RSR. GTs must weigh at least 2,480 lb and generate from 400 to 500 hp, giving them top speeds up to 180 mph. They carry yellow leader lights and markings on their rear-wing endplates, mirrors, and windscreens.
Grand Touring Challenge: The GTC class includes three types of Porsche 911 GT3 Cup cars, all based on the road-going Porsche 911 GT3 RS. With top speeds of up to 150 mph, the minimum weight depends on model year and specification, but the 2010 entry, for example, must weigh at least 2,655 lb. GTC cars have red leader lights and yellow car numbers.
Keeping it close
Officials running ALMS strive to keep races competitive. In fact, they want no more than a 0.5% difference in lap times between the fastest and slowest cars in each class. To even things up, they have three choices: adjust the restrictors on the air intakes by about 1 mm, limiting engine power; add weight, up to 110 lb; or limit the size of the fuel tank, which could necessitate more pit stops. Restrictions and limits are placed on cars at the start of each season, but officials meet every month and restrictions can change during the season.
For example, last year, judges let teams running Porches boost the size of their air restrictors by 0.3 mm because they seemed to be running slower laps. They also took away a 35-lb weight penalty from the Corvettes in return for a promise from those teams to keep their engines a little more stock. And M3s enjoy slightly larger restrictors based on their large frontal area, which makes them less aerodynamic than other, lower-built cars, such as Corvettes and Ferraris.
And sometimes officials can be a bit unpredictable, notes Jay O’Connell, technical director for the BMW-Rahal Team. “We finished second and third in a race, so we didn’t win. But we still got hit with a 55-lb penalty. We did have the fastest lap, but we never could catch the Ferrari that was a lap ahead of us.”
Several companies are partnering with BMW and RLL Racing to make it possible to field two M3 racers in the ALMS Series this year. They include: