You’ve no doubt read about Subaru’s insane Prodrive-built WRX STI Type RA hill-climb/rally/general-insanity car, but now the car—in NBR Special trim—has become the fastest four-door at the Nürburgring Nordschleife with a time of 6:57.50, an in-depth look is in order. (Click here to see video of the lap.)
You may associate the car with rally driver Mark Higgins, who sets the four-wheeled record at the Isle of Man as often as he drives to the drugstore. He recently went for the timed record at the Goodwood Festival of Speed but was narrowly beaten by a Jaguar XJR 12D Group C car and a Penske PC22 CART car (so yeah, he can be forgiven for missing the gold). But Subaru called on a Nürburgring specialist to set that record: 25-year-old Richie Stanaway, whose most recent Nordschleife race was for Aston Martin in the FIA World Endurance Championship. Here’s what Subaru gave him to work with.
Hydraulically Activated Wing
Pneumatic actuators fire the Gurney flap at the back of the wing up and down in milliseconds, either manually via a button on the steering wheel or in response to the ECU, which reads data from various sensors (speed, steering angle, brakes, accelerator). A computer-controlled valve lock holds pressure, and carbon-fiber control rods move the wing. When dropped, the result is the equivalent of a 40-horsepower boost at Vmax. If something goes wrong, the default position is up, where it holds firm against 180-mph wind. It’s possible to program the actuation entirely automatically, but since a confident driver is a fast one, the driver has the final say. “You let them do it and then they feel more involved,” says Prodrive’s senior rally engineer Richard Thompson.
Maybe rowing the gears through an H pattern sounds normal to you, but in the world of rally racing, it’s quite rare indeed. Prodrive worked with Xtrac to create a one-off transmission that shifts through an H pattern yet is able to bang off same-rail shifts in 20 milliseconds (with each dogleg shift taking about 30 milliseconds), with the actuators mirroring your hand movements. Why, you ask? Spin recovery. It’s surprisingly time consuming to click back down through the entire gear tree of a sequential gearbox to start from 0 mph (or close). Here, if the driver spins the car while in sixth gear, a twist of one button gets him back to neutral. The weirdest part about this being a truly automated manual transmission might be that, after the car is shut off, the system runs through a 30-second check phase, wherein it effectively “wobbles the gear lever to find where neutral is,” Thompson says—just as you might in your street car—before depressurizing the system as mandated by the FIA for safety.
Unlike the WRX STI in your nearest showroom, the 600-hp NBR Special revs to 8500 rpm, which exactly matches the car’s top speed of 180 mph (Stanaway got to 178 mph at 8409 rpm during the record run). Prodrive says that the car can manage 8750—or maybe even 9000 rpm—it just depends on top speed during a lap. If the driver finds more, then the revs go up. If it happens in future runs, it’ll be for Higgins on the Isle of Man’s long Sulby straight on the west side of the island, where he’s on sustained throttle for 30 seconds at a time, and for Stanaway on high-speed Nordschleife sections that will see sixth gear, like Tiergarten.
Blowing Head Gaskets on Purpose
Sort of. On full boil, the cylinder pressures get extreme—like, heads-lift-off-the-block-deliberately extreme. To control this sort of chaos, Prodrive machines a brass detonation ring into the cylinder bore and uses a Garlock ring on the head-to-block interface. Just in front of that, the cylinder pressure is plumbed into a small manifold and measured with a pressure sensor. The engineers can see tiny pressure spikes immediately when the heads lift and then map things like turbo boost and ignition timing to hover right at that very ragged edge. “If it’s your last run and you’re really fighting for those last few seconds,” says Thompson, “then we can map to that with a slight amount of head lifting.” It goes without saying that this engine gets rebuilt after each event. This time at the Nürburgring, though, the team ran out of tires and time. They’re sure there’s a faster lap in the car, but we’ll have to wait and see.
Relatively Primitive Anti-Lag
Turbo lag is a relative thing. Prodrive says that the NBR Special is laggy compared with the road car, but with that said, it still manages about double that car’s boost pressure anywhere in the rev range. Still, you want to keep the turbocharger on boil between shifts. Here, a “rocket” (as designed for World Rally Championship competition) is not employed, as the needs of the NBR Special are very different from those of a stage-going rally car. Rally cars see FIA-defined stage-average speeds of about 80 mph, with lots of twists and turns (read: throttle lifts). There’s a 34-millimeter restrictor in place, which cuts the air to around 60 percent of the roadgoing car’s. Torque and drivability at the bottom end are key in the restricted rally car. Here, it’s just not needed, so a system not dissimilar to that of modern turbocharged road cars is applied, retarding timing and messing with the fuel cutout to generate somewhere between 7 and 9 psi at closed throttle—plenty when your shift times are 20 milliseconds.
Even the windshield-wiper motor has been relocated to a space deep in the passenger footwell, giving you some idea of how serious the quest for a lower center of gravity is. Nothing can be mounted high up in the car, not even the intercom. A steel roof is mandated for the competition car, but the limited-edition STI Type RA that will be offered to customers has a carbon-fiber roof panel (but not, of course, many of the NBR Special’s modifications). Carbon-fiber body panels replace the stock gear just about everywhere, and a carbon-fiber dashboard makes up the entirety of interior luxury. Every nut and bolt is assessed and counterbored as necessary to shave ounces. Many hours of work go into lightening the A-, B-, and C-pillars and the cabin rails (the roll cage provides most of the structural rigidity). Glass is replaced with four-millimeter Perspex as regulated by the FIA. All told, the rigid 600-hp ’Ring racer weighs about 2425 pounds.
The Paint Doesn’t Weigh Anything, Either
It’ll come as no surprise to learn that this is no show-car paint job. There’s no clearcoat, and we’re talking one layer of color at most. The paint people are really good at just doing “one or two wafts of the gun, getting it shiny but with micro-thickness paint,” Thompson says. He estimates that the NBR Special’s paint might be 25 percent of the thickness of a roadgoing car’s. Think of a road car using a couple gallons of paint at perhaps 8 pounds per gallon—being frugal with the spray gun can save significant weight.
Those big 9.0-inch-wide slicks generate a heck of a lot more lateral acceleration than the tires on a rally car—the racer can pull 1.2 to 1.3 g in the dry, according to Thompson. This puts a lot of pressure on the side of the damper tube, creating friction. To remedy the issue, Prodrive redesigned the dampers with one roller bearing pack on the top of the unit and one on the piston rod on the bottom, resulting in a very low-friction damper. That’s expensive and rare, but what’s more common in racing is the big spherical roller bearing supporting the top mount, which allows turning without much friction during moments of high g’s. As in rally cars, all the steering and suspension rubber has been replaced with thrust washers and roller bearings to allow the smooth movement of the wheels. Says Stanaway of driving the NBR Special: “The other thing that you can feel that’s different to most cars is that I can put the power down in the corners—I don’t have to wait, so I’m instantly on the power.”
Saddlebag Fuel Tank
Despite making 600 horsepower, the NBR Special is not direct injected. We’re told that’s an upcoming logical evolution, but in the meantime you can bet Prodrive has done all it can to maximize and equalize pressures in the port-injected system. A Kevlar fuel bag straddles the prop shaft, creating the need for two parallel fueling systems with no fewer than four low-pressure pumps feeding two collectors into four high-pressure pumps. The total bag capacity is 70 liters (18.5 gallons), with 40 of that above the divide. McLaren makes the fuel injectors, and all Prodrive will say about them is that they’re much bigger than stock.