As You Requested: Nissan GT-R LM Nismo Prototype Revealed

Cars, News I By Tom Martin I February 02, 2015
While The Stones sang that “You can’t always get what you want”, they added that “If you try sometimes you just might find you get what you need”. With Nissan’s unveiling of the GTR-LM (during the Super Bowl, interestingly) WEC LMP1 endurance racing may indeed get what it needs.
Back To The Future
In discussions with many racers and racing enthusiasts, we’ve heard a fairly constant refrain asking for a return to the 1962-1972 period of seemingly wild and rapid innovation in race car design. Ford vs. Ferrari at Le Mans.  Front engine vs. mid-engine vs. turbine car at Indy. Aero experimentation in F1. And, best of all, Chaparral Cars vs. Lola, McLaren and Porsche in Can-Am.  These cars were each the pinnacle of their respective formulas, but even more you could see the innovations without having to stare at computational fluid dynamics output on a screen.
Up until now, LMP1 has offered some nifty variety at the front of the field. Each of the top three cars sports a different powertrain technology. Audi runs a hybrid based around a diesel engine, Toyota uses a normally-aspirated gasoline V-8 in its hybrid powertrain while Porsche uses a gasoline fired turbo V-4.  That’s cool, but a bit under the skin and tough to see.
Ben Bowlby Returns
LMP1 class endurance racing just got a visible shot in the arm courtesy of Nissan and their design team led by Ben Bowlby. Bowlby, as you may recall, penned the radical DeltaWing car that ran in the ACO’s experimental “Garage 56” slot at Le Mans and now runs, as develop by Elan, in IMSA’s Tudor United Sports Car Championship. He also devised the related Nissan ZEOD RC electric prototype racer.
The hallmark of both these cars was a very narrow front track to generate low drag. To go with this, Bowlby fashioned a layout that made much more use of the rear of the car to do the work. Laypeople looked at the car and said “that can’t work”, but Bowlby knows his physics and the DeltaWing did roughly meet its objectives of LMP2 pace with half the fuel consumption.
The Nissan GT-R LM Nismo is not a Garage 56 entry. This time Nissan and Bowlby are going for the big prize, overall win at Le Mans. And they’re going up against the big hitters of Audi, Toyota and Porsche.
DeltaWing In Reverse?
Modern racing is rules-based racing. While some decry this, really it was always this way, if for no other reason than the rules of physics and the constraints of existing technology.
Bowlby has looked at the rules and asked if they favor a different car layout than is commonly used. He thinks they do.
Before diving into why, let’s first review the basic points of the GT-R LM so you have a reference point:
. Front-engine
. Engine drives front wheels
. Front tires 14” wide
. Rear tires 9” wide
. Dual flywheel hybrid energy recovery system
. Rear wheels powered by electric motors
As a summary, this is a standard LMP car in reverse. The GT-R has a front mid-engine layout; Audi, Toyota and Porsche have a rear mid-engine layout. The driver is forward in the chassis on standard LMP cars, the driver is rearward on the Nissan. Loads are front-biased on the GT-R, rear-biased on the others.
Some of these ideas have been tried before, though perhaps never in such a radical combination. The Panoz LMP-1 of the late ‘90s comes to mind. And certainly the Toyota Eagle MkIII IMSA GTP cars before that showed some aero concepts that may be applied to the GT-R LM. The Eagle, which looked like a bar of soap, actually worked out a way to make the front section of the car very efficient by using a very narrow tub to maximize air flow coupled to a ground effect front section and tunnels to exhaust the air behind the front wheels. Hence we may refer to the front of the car as a diffuser. 
You need to ask at this point, why bother? And besides the fact that Bowlby obviously enjoys unconventional thinking, the answer is basically aerodynamics. Bowlby thinks that he can create greater aerodynamic efficiency (critical at Le Mans) by concentrating on what is basically a front-diffuser car. The ACO’s rules, which pretty clearly assumed a standard design, leave some options to make a better set of aero systems at the front than at the rear. Or so he believes.
The reason that there is uncertainty here is that a front-engine car creates all sorts of packaging issues for the front diffuser and tunnel system the engineer is designing. In simple terms, the trailing edge of the front diffuser wants to be in clear air, but putting a big V-6 right behind the diffuser works against this requirement, so the engine is pushed back in the Nissan. You have to fit a driver in there somewhere as well, and speculation has him surrounded by some of the running gear. Finally, to make the tunnel system work exceptionally well, the engineers have incorporated a structural tunnel section on the rear portion of the car. As a result, the rear suspension has to be mounted outside the tunnels, using drop-gear uprights to get the rear halfshafts outside of the flow path. Not all the innovation on the GT-R LM is visible, to say the least. 
But if Nissan can make all this work to get more downforce with less drag, they start with an advantage. From that starting point, Bowlby’s team has proven they are masters of balancing the car around a completely different set of assumptions than are normally used.
Not Underpowered This Time
The GT-R also attempts to score a second advantage over its competitors, again based on exploiting the rules. The ACO offers four energy classes within LMP1-H: 2 MJ, 4 MJ, 6 MJ and 8 MJ. These designate the amount of energy (in megajoules) released from the ERS system during one lap of Le Mans (the reference track). Audi uses a 2 MJ sytem, Porsche and Toyota use 6 MJ systems. Nissan is building an 8 MJ system. The more ERS energy you use, the less fuel you get to burn. But here is the catch: the ERS energy isn’t offset by fuel in a 1:1 ratio. The bigger ERS systems can expend more total energy and thus should be faster. In simple terms an 8 MJ car has more total power than a 2 MJ car.
To put this in standard terms, Nissan is believed to have built a car with between 1200 and 1500 total hp. About 500-600 comes from the V-6 and 700 to 1000 from the ERS system. Of course, with ERS you don’t get that power boost for as long as you want it, but an 8 MJ has more ERS energy than its competitors.
For perspective, a 2 MJ system is worth about 1.6 seconds a lap over a pure internal combustion powerplant. A 6 MJ system raises that to 4 seconds a lap. And an 8 MJ system is theoretically worth 7 seconds a lap.
Clearly if you could count on the ERS system working flawlessly, you’d run an 8 MJ system. But you will note that Audi won Le Mans last year with a 2 MJ system. Audi is hurt the least if the ERS system fails or overheats, which is the flip side of choosing a system like to show slower qualifying pace. “To finish first, first you must finish.”
It isn’t all about ERS either. The ACO regulates total fuel used per second by the engine. Nothing else, not power, displacement or configuration. So Nissan has designed a very efficient gasoline engine to try to produce more power per gallon of fuel, which should translate to more power per lap.
Development Makes The Difference
With all these new approaches, the Nissan GT-R LM Nismo is bound to have teething issues. The designers have to get the weight of the car down. They have to make a new flywheel system work. They have to balance the car out. And then there is actual track testing which has the nasty habit of upstaging computer models.
But, barring immediate failure on race day (something Bowlby’s projects have experienced in the past), if you like variety and uncertainty this year should be one for the history books at Le Mans. We can’t wait.


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