||March 17, 2016 16:23
||September 07, 2016 09:42
New Sports eXperimental
As the first true Japanese supercar, the 1991 Acura NSX represented the pinnacle of Honda's road car technologies. Designed to suit the driver like no car before it, the NSX claimed a myriad of groundbreaking features. Based upon the principal of "Man maximum, machine minimum", the NSX wielded a formidable arsenal of technologies in order to achieve Hondas goals:
- The NSX was the world's first all-aluminum mass-produced automobile. This minimized the body weight of the vehicle. Achieving a "supercar" power to weight ratio was critical to the project.
- Along those lines, to balance the requirements of maximum power and minimum weight while simultaneously maintaining a linear response, a high revving, naturally-aspirated V6 was specified. This engine featured an all-aluminum construction with titanium connecting rods and a DOHC VTEC valvetrain. Maximum output was 270hp from only 3.0L of displacement, and it revved to over 8000rpm.
- The NSX was mid-engined, in order to centralize the mass and minimize the yaw moment.
- To provide a very low center of gravity, the V6 engine featured a 90-degree vee angle, which also kept the deck height as low as possible.
- The NSX's cockpit was designed to serve the driver – modeled after a fighter jet cockpit, with very thin pillars and lots of glass to optimize visibility.
- The NSX was designed to be docile enough to be suitable for everyday use, while maintaining the potency to challenge the world's greatest automobiles on a racetrack
New Sports eXperience
More than 20 years following the original NSX's introduction, Acura revealed the concept for the next generation NSX at the 2012 North American International Auto Show. The concept that was shown was stunning, but the few technical details that were revealed made it sound like a much different car from the original NSX:
- The new NSX would be AWD
- It would feature a V6 gasoline engine, with direct injection
- It would be a hybrid, with 3 electric motors
To put it bluntly, none of these things really sounded very intriguing, especially in the hyper-performance atmosphere of the modern supercar. Our primary concern was weight and the ultimate toll it would take on performance. Being AWD and a hybrid, how on earth could they possibly keep this car light in weight? It turns out that the new NSX is not exactly a flyweight, but the good news is that it drives like a much lighter car. The hybrid thing had us quite worried as well, and not just because of the additional weight. The problem was that even the "sportiest" hybrids we had tried to that point were largely duds to drive, with more compromises than advantages. We just couldn't imagine saddling a so-called "supercar" with e-motors and a battery that would be potent enough to contribute. It turns out that Acura's not the only one who figured it out. Porsche, Ferrari, and McLaren all seem to have worked things out quite nicely in that respect as well.
As the R&D team was quietly laboring away on this new project, we began to catch whiff of some interesting rumors concerning the powertrain. Even though the original concept indicated a normally aspirated transverse V6 configuration, we quickly began hearing that the design team decided that turbochargers would be necessary. And in order to properly package the new turbocharged engine, the entire package would have to be rotated 90 degrees, into a north-south (longitudinal) orientation. Acura ultimately confirmed these rumors in late 2013. Acura also began talking more about the new NSX's "zero delay response" and how it "immediately responds to the will of the driver"
This powertrain design change meant that the body had to be redesigned from the original concept. The original concept's elegant air intake openings aft of the doors became considerably larger, in order to feed a pair of huge intercoolers. To fit the 9-speed dual-clutch transmission behind the engine, the car had to be lengthened (+3.1"), while slightly stretching the wheelbase (+0.8"). The width (+1.0") of the car also increased in the process. Fortunately, the design team (headed up by Michele Christensen) managed to keep the car's gorgeous styling and even enhance the aggressiveness a bit.
JNC1 - 75 Degrees
As with the original NSX, the engineering team was aiming to keep the new NSX's center of gravity as low as possible. And again, the powertrain configuration was a crucial component in achieving that goal. Acura already had the J-series V6, a family of 60-degree V6s they could have tapped, but a 60-degree V6 would have been too tall and the center of mass would have been too high to meet the goals of this project. A 90-degree V6 (as in the original design) would have indeed offered a very low center of mass, but then packaging the duo of turbochargers on the outside of a 90-degree V-6 was suboptimal, as it would have required the NSX to be even wider. It turns out that an unusual 75-degree bank angle provided the optimum configuration for the project, and the fitment of a dry sump lubrication system allowed them to mount the engine an additional 2.4" lower within the chassis – in fact, the crank centerline of the engine is located below the plane of the axles. This engine is designated as JNC1, and it is pretty much a street legal racing engine. The block and heads are manufactured by Cosworth. The JNC1 features dual overhead cams with VTC (Variable Timing Control) on both cams. Interestingly, there is no valve lift control (VTEC) on the JNC1. The JNC1 also features a forged steel crank, forged steel connecting rods (manufactured by Pankl, of Austria), forged steel intake valves, forged steel (and sodium-filled) exhaust valves, cast aluminum pistons, and plasma transferred wire arc thermal spray lining the aluminum cylinder walls (this process saves over 7lbs of weight vs cast iron cylinder liners). The engine features a combination of direct injection as well as port fuel injection, and as mentioned, there is a pair of single scroll turbochargers (peak boost: 1.05bar, 15.23psi) featuring Inconel turbines and electric wastegates. The intake charge is cooled by a pair of sizeable (each one has an area of over 880cm2) air-to-air intercoolers. The intake manifold uses a two-into-one design with twin throttle bodies. It's done this way in order to minimize torque deviation between the two cylinder banks. Sandwiched between the engine and 9-speed dual clutch transmission is a direct drive electric motor, capable of contributing up to 47hp and 109lb-ft of torque.
The NSX features a lightweight dual path stainless steel exhaust system. The path of the exhaust is determined by mode of IDS (Integrated Dynamic System) that the driver has selected. In "Quiet" and during easy driving in "Sport" mode, diverter valves in the exhaust system route the exhaust gases through a pair of silencers on either side of the rear of the engine. These silencers are attached to the outer two pipes on the NSX's 4-pipe exhaust. If the driver has selected Sport+ or Track modes, the silencers are bypassed and the exhaust takes the shortest path, straight to the center two exhaust pipes at the rear of the NSX. Also, during high performance driving conditions in "Sport" mode, the system will selectively bypass the silencers. Similarly, there is a sound pipe attached to the intake manifold which permits the driver to hear the true intake sounds. This too is actuated by a valve in the intake system, and is the various modes and volumes are controlled by the vehicle's IDS system. The difference in maximum SPL (sound pressure level) in the cabin when switching from "Quiet" mode to "Track" mode can be as high as 25dB.
Acura refers to the NSX's body as a "Multi Material Body/Frame". It is basically a spaceframe composed of ablation-cast aluminum nodes, with mostly aluminum frame members, and a smattering of ultra high strength steel pieces along the roof pillars. Body panels are a mixture of aluminum and SMC (sheet molding compound). The floor panel features a carbon fiber core. The resulting structure is extremely rigid - in fact it is two to three times more rigid in static and dynamic measures than its closest benchmark. This level of rigidity is considered crucial in the pursuit of delivering the NSX's "zero delay" responses.
Twin Motor Unit
In order to provide the NSX with its torque vectoring AWD capabilities, a TMU (Twin Motor Unit) drives the front axle. First seen on the rear axle of the RLX Sport Hybrid, this device is what gives the NSX its incredible yaw control abilities. As the name implies, it uses two motors mounted in a single housing with a planetary mechanism that allows the motors to decouple when necessary (at very high speeds) but they can also provide on-demand torque vectoring at any speed. The motors are rated at 36hp and 54lb-ft each, which sounds very similar to the motors in the RLX's TMU. The motors in the NSX have a higher maximum operating rpm (15000rpm) and the gear reduction ratio of 8.5:1 in the NSX's TMU is different from the RLX's TMU reduction ratio.
Continue to the next page to read our first street and track impressions