Nissan debuts front-engine, front-drive GT-R LM Nismo racecar

  • 17-Feb-2015 11:09 EST
Nissan_GT_R_LM_NISMO_09.jpg

The Nissan LM Nismo racer's vaguely lumpy lines only hint at the innovative thinking cloaked beneath them.

“Outrageousness.” It was the signature line of 1980s Chicago Bears quarterback Jim McMahon, the self-described “punky QB.”

Seems like he might have made an impression on unorthodox racecar designer Ben Bowlby, who has followed up his iconoclastic DeltaWing racer with a second act that is equally shocking. Outrageousness, indeed!

Nissan revealed Bowlby’s new GT-R LM Nismo (shorthand for Nissan motorsport) hybrid Le Mans racer in its tear-jerking Super Bowl commercial depicting an often-traveling racer dad and his son. (See it at www.withdad.com)

Unlike the DeltaWing, the extent of the LM Nismo’s unorthodoxy wasn’t so obvious in the commercial, aside from the flicker of flame from exhaust pipes exiting the top of the hood, ahead of the driver.

After creating the DeltaWing, Bowlby was lured to Nissan (which supplied race engines for the DeltaWing) as team principal and technical director, where he designed the DeltaWing-lookalike ZEOD RC. When DeltaWing managing partner and longtime sports car racing stalwart Don Panoz sued, it is easy to imagine the powers-that-be at Nissan directing Bowlby to design an all-new car that is so completely different from the DeltaWing as to be immune to legal challenges.

Bowlby certainly delivered, succeeding the narrow-front, rear-drive DeltaWing with a front-engine, front-drive LM Nismo that packs most of the car’s working hardware over the front wheels and tows the driver capsule along behind like a chariot.

“In order to get a high-performance outcome…we’ve turned the whole concept of the conventional [Le Mans Prototype] car of 2014 on its head,” Bowlby crowed.

Rule dictated approach

The reason to do this was driven by the rules, according to Darren Cox, Global Head of Nissan Motorsport. In a bid to curtail speeds, rules makers have specified narrower tires and have closely restricted the ability of designers to build cars with significant downforce at the rear. That’s where the downforce is needed on conventional Le Mans prototypes, because that is where their mass lies.

The rules regarding the aerodynamics at the front of the car are very much more wide open, Cox said. “So we were trying to get the weight over the front of the car because it is a little more open.”

Putting the engine up front and sending the power to the rear would compromise the car’s downforce-producing underside, with a long driveshaft interfering with the airflow, so it made more sense to just power the front wheels, he explained.

While rear downforce on mid-engined, rear-drive cars is limited by regulations, those same restrictions don’t hurt the LM Nismo as much because of the absence of drivetrain hardware at the rear.

The move to exploit the availability of front downforce by moving the mass of the drivetrain forward has had the side effect of making more rear downforce available too.

There’s a twin-turbo, direct-injected 3.0-L, 60° V6 power plant up front, bolted to a five-speed sequential transaxle, with power transferred through a Tilton Engineering four-plate carbon clutch pack.

That engine is very efficient, according to Bowlby. “It produces a large amount of power using the allotted fuel flow limit,” he said. “The fuel flow limit is one of the new regulations at Le Mans. We’re not limited by the engine capacity or the boost pressure or the rpm of the engine; we’re limited by how many grams of fuel per second we can burn.”

That makes engine efficiency crucial. “We are burning a smaller amount of fuel, around 30% less than was used by a gasoline engine at Le Mans in 2013, for example,” Bowlby said.

A Cosworth engine control unit monitors the engine and gearbox, while still other computers oversee the driver-adjustable traction control, a system for minimizing turbo lag, brake-by-wire, throttle-by-wire, and the hybrid-electric system’s energy recovery system. Cosworth also provides the data acquisition and driver’s display system.

Where sports car convention puts the racers on 19-in wheels, the Nismo’s magnesium BBS center-lock wheels are 16 inches in diameter. Even more daringly, the fronts are 13 inches wide, compared to 9 inches in the rear.

Those bigger tires carry more of the burden of the car’s mass and aerodynamic downforce, and along with the drivetrain contribute to an overall profile that is blunt at the front and tapered at the rear. If the DeltaWing’s aerodynamic inspiration was an archer’s arrow, the LM Nismo’s is a raindrop.

“We have moved the weight bias forwards to give us traction for the front-engined, front-wheel drive,” said Bowlby. “We’ve also moved the aero forward to match the weight distribution. So the aero center of pressure, the mass center of gravity, and the tire capacity are all in harmony.”

The smaller-diameter wheels permit the Michelin tires, which have the same outside diameter as the tires used on more conventional LM P1 contenders, to run lower air pressure than would otherwise be possible, for better grip.

Odd-sized Michelins will measure up

The racing tire experts at Michelin were already friends with Ben Bowlby from their work together on the DeltaWing endurance racing project. “We were contacted quite a while ago by Ben Bowlby,” reported Nicolas Goubert, Technical Director for Michelin Motorsport. “We are used to working out of the scope on different projects with him.”

Indeed. The dart-shaped DeltaWing mounted a pair of almost motorcycle tire-sized front tires close together at its front and a more conventional pair at the rear. It required Michelin to develop tires of an entirely unique diameter for the DeltaWing’s small 15-in wheels rather than the 18-in wheels on other prototype racers.

The skinny fronts were just 10 cm (3.9 in) wide and stood 58 cm (22.8 in) high, compared to the 36-cm (14.2-in) wide and 71-cm (28.0-in) high 18-in tires at the front of other cars. The rears weren’t quite so different, at 31 cm (12.2 in) wide and 62 cm (24.4 in) high, compared to 37 cm (14.6 in) and 71 cm (28.0 in) for the 18-inchers.

“The DeltaWing was very interesting, tire-wise,” Goubert recalled.

Secrecy was a big part of Nissan’s plan for the LM Nismo, which meant it couldn’t just send a car over to Michelin’s shop for the company to develop its bespoke tires. But with modern computer-aided modeling tools, tire makers only need some fundamental characteristics to produce tires, according to Goubert.

The vertical loading, longitudinal force, and lateral force over the course of a lap describe the tire’s needs sufficiently. Unlike the DeltaWing, the LM Nismo’s design didn’t inherently call for great unorthodoxy beyond the plan to run narrower tires at the rear, but the loads expected pushed Michelin engineers toward a new solution.

“[Bowlby] didn’t have a precise idea of what he needed,” Goubert recalled. “It was a question of deciding together.” Bowlby anticipated running last season’s narrower conventionally sized front tires, with a 31-cm width and 71-cm outer diameter. But with the driveline loads and aerodynamic downforce applied, conventional tires on 18-in wheels would need to run very high air pressure, sapping their grip.

Michelin’s proposed solution: 16-in wheels inside tires that are the same size on the outside. That increased air volume inside the tires would support the high loading at lower pressure, preserving traction.

Meanwhile, at the rear, the car carries little weight, applies no acceleration, and needed to clear out of the way for air to slip through as effortlessly as possible. So the solution there was to narrow the tires to a paltry 20 cm (7.9 in) each. That leaves them twice as wide as the DeltaWing’s fronts, but still less than two-thirds the width of the fronts.

Wheel diameter front and rear is 16 in, with 14-in-wide BBS front wheels and 9-in-wide rears.

Will these tires prove up to the task, providing competitive grip and durability, while wearing evenly so the car’s front-to-rear balance remains consistent throughout a driver’s stint?

“If the simulations are right, each tire size is adequate to the strain the tires are going to see,” Goubert said. “We have designed them to be as durable [as the company’s conventional tires] in the number of stints they will be able to do.”

Stronger electric drive

The smaller wheels are enabled in part by the car’s ability to use smaller brakes because of its stronger regenerative braking. Other cars need huge rotors to dissipate heat from their brakes, but the Nismo is built to the FIA’s 8-megajoule standard, which gives it a bigger electric motor for its hybrid drive system.

This not only means that the larger electric drive system can provide more boost accelerating away from turns, but that it can also arrest more speed as the car brakes into those turns, leaving less inertia for the conventional brakes to dissipate.

The LM Nismo competes in the hybrid category that permits use of a maximum of 8 MJ of energy per lap, the highest category. There are hybrid classes for 2, 4, 6, and 8 MJ, with correspondingly less fuel permitted for the internal-combustion engine when more electric power is allowed.

But the regulations are calculated to give slightly more electrical energy advantage compared to the allowed fuel volume, according to Bowlby. “If you choose to recover more [electrical] energy, you actually end up with more total energy even though your fuel energy has been cut slightly,” he said. “So if you are an 8-MJ car compared to a 2-MJ car, you should be faster over the course of a lap.”

That energy advantage, however, is offset by the increased battery weight that comes with the extra electric power. Weight is murderous to Le Mans lap times, costing about half a second per lap for every 10 to 12 kg (22 to 26 lb) of extra mass, Bowlby explained.

With its heavy battery pack, electric motor, and conventional internal-combustion drivetrain, the powertrain components in the LM Nismo will account for half the car’s weight, he said. “We’re going to be really challenged to make our weight target of 880 kg for 2015.”

Driver Marc Gene has been behind the wheel testing the LM Nismo, and he has found the car to be as dramatic a departure as it looks. “It looks like Nissan read a different rule set!” he said. “I think this is what allows Nissan to see things in a different way than the other manufacturers.”

Naturally, the car drives differently from the rear-drive cars Gene has raced in the past. “It feels different because it is a different concept, but it has a lot of advantages, especially if you look at both [fuel] consumption and straight line speed,” Gene noted. “This type of concept is the best in that area.”

As the race at Le Mans nears, testing will reveal whether Nissan’s and Bowlby’s bets have paid off. Cox thinks that the car, as with Team Penske’s unexpected Ilmor Mercedes pushrod cam-in-block engine’s appearance at the 1994 Indianapolis 500, has exploited a known opportunity in the rules that has been overlooked due to other teams’ inertia.

“We think we’ve got our sums right,” Cox said. “Our competitors think they’ve got their sums right. Someone’s going to be right and someone’s got their sums wrong and we’ll find out.”

Whichever way it goes, it should be outrageous.

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