Building a Privateer GT3 Nissan 370Z

Back in 2018, Valkyrie Autosport’s 370Z wasn’t quite ready for ES. It was still stuck in E0, where it had demonstrated dominant pace on a regular basis. In fact, it had been been quick enough to lock down third place at that year’s 25 Hour — even after a rogue rock fired through the engine bay and wiped out the alternator.

Clearly, the platform was reliable enough to keep Brian Lock’s rent-a-ride business running smoothly and predictably, and perhaps he could’ve cleaned up in E0 with a little luck, but he couldn’t deny an urge to move into a more competitive category.

The plan for 2019 was simple: bump this homebuilt Nissan into the ES class, and try to find some GT4-rivaling straight-line speed. Rather than try to stretch the Jim Wolf-built motor beyond the reliable state it was in, Brian opted for a more efficient gearbox. The reliable factory six-speed wasn’t cutting it any longer, and after a stillborn experiment with a sequential, he contacted a British team competing in the British GT series with a Z of their own.

RJN Motorsport had fitted their 370Z GT4 with a Hewland paddle-shifted box, and Brian wanted to follow suit. This Hewland offered cost-effective and race-proven solution to improve speed and drivability—the latter a consideration a team owner must make when renting their car out to clients of different skill levels.

Sadly, this transmission didn’t integrate into the homebuilt car so smoothly. Not only was the motor producing a torque figure close to gearbox’s limit, but the limited set of available ratios were too wide.

“We tried shipping it back to the UK for some tweaking, but it turned out to be more headache than it was worth. The experience taught us a lot, though: that these gears could only be spaced so far apart for clutchless shifting, that the programming of these boxes is extremely complicated, and that shipping a gearbox across the Atlantic is very costly,” Brian recalled.

Fiddling with a frustrating gearbox had its perks, though. Lap times dropped by about two seconds with this transmission—putting it just ahead of the GT4 competition. In fact, with the motor making 390 horsepower at the rear wheels, it’d be fair to say it was nearing GT3 territory.

At the end of 2019, Valkyrie’s troublesome term with the Hewland came to an agonizing end. The steep drop in revs with every clutchless shift strained the drivetrain, and during the 20th hour of that year’s 25 Hours of Thunderhill, the differential finally broke. This setback didn’t have much effect on its finishing position, but it still irritated Brian enough to begin seeking out a better solution to the 370Z’s shifting problems.

Switched On During the Off-Season

COVID, for all its setbacks, at least provided Brian plenty of time to give this car the overhaul it deserved. For that year, the Valkyrie 370Z was, as Brian said, “on timeout.”

That didn’t mean that Brian used the lull to relax. The man built his own house in his free time, so it’s safe to say he’s not the type that enjoys lounging around too long. He took advantage of 2020’s looser schedule to plan a new path toward his goals, and with Gary Baker onboard, a new business partner who shares the same vision of a homebuilt GT3 car, he started making major moves as the pandemic put the racing world on pause.

Following that painful ending to the 2019 25, Brian was finished with the flawed Hewland and wasted little time replacing it with a pricey but robust Holinger sequential. Thankfully, this upgrade marked the start of steady improvements with the car, giving it some headroom for the anticipated power gains as well as added versatility thanks to a broader selection of available gearsets.

With the Holinger’s optimized gearsets, it was dropping less than 1,000 revs between shifts and trimming another second off the Z’s lap times. This helped Valkryie bounce back from a difficult winter and look forward to their first race in nearly a year: the WERC 5-Hour at Thunderhill.

There, a long duel with Porsche GT3 Cup running in the ESR-class demonstrated just how capable the Nissan 370Z had become. The cornering speed and braking performance were there. The Porsche could not leave them in any corner. However, the Porsche still had the Nissan beat on power and fuel consumption. Brian walked away with his head held high that day, even though he knew he’d soon have to deal with the brakes that he and his drivers had to melt to pass the Porsche.

“That day, watching the Porsche’s performance made me realize that attaining the big numbers is only part of the solution. The Porsche, which has direct injection, beat us on pit stops. The extra speed down the straights made it easier for them to maintain their equipment, too. That was when I realized that the faster you go, the more the little details make the difference,” Brian proclaimed.

More Spring, Full-Stop

To build upon its strengths, Brian began optimizing the aero package. Without the budget for a CFD guy, he has to observe factory GT3 cars for inspiration. Coincidentally, the 2019 25 Hours of Thunderhill left the car battered and in need of a rebuild, so he went the extra mile with some new bodywork.

First came an IMSA-inspired widebody kit consisting of new skirts, rear fender reliefs, and a new rear bumper bolted to a more efficient diffuser. Expecting to have to compensate for greater downforce, he started searching for stiffer springs, but soon realized he already owned the stiffest springs available.

That switched on the lightbulb upstairs. If there weren’t any stiffer off-the-shelf options available, there had to be more to tuning these high-downforce machines than just altering spring rate. There had to be. As per usual, Brian did his homework first, then addressed all the other limitations within the entire suspension setup.

After a complete shock revalving and new set of three-way adjustable JRZ shocks for the front end, Brian began exploring the opportunities offered by more aggressive bump stops. GT3 cars, being heavily aero dependent for their cornering speeds, have limited suspension travel, often running on the bump stops.

Provided he could keep the car from pushing too much through the slower corners, he felt the 370Z would be flatter, more willing to change direction, and much more confidence-inspiring in the faster bends. Even if the setup yielded a little slow-speed understeer, the gains in high-speed corners would still probably yield a faster lap time.

That assumption was confirmed when Valkryie was finally able to test the car later that year. The new shocks, bump stops, and aerodynamic additions helped Brian find lots of time — at a very bumpy track that punishes a machine with insufficient compliance: Buttonwillow.

There, the stability in the fast sweepers and hard braking zones helped Brian find another 2 seconds. The added stiffness also kept him from having to rebuild his splitter, which was, up until then, a task he’d gotten quite familiar with.

The Missing Element

A slow winter followed, but Brian was kept engaged in the program with plans for a new motor. After lots of late nights spent chatting with the eminent Clark Steppler at Jim Wolf Technology, he wrote out a large check, sent it to his preferred engine builder, and waited for a new package to arrive on his doorstep.

When it finally arrived, Brian had to pinch himself — he was the first in the country to receive a VQ like this. Semi-experimental and very trick, this 4.2-liter lump featured a 14.7:1 compression ratio and a redline of 8,000 rpm—where it made 485 horsepower. Carrying it to that lofty redline was a broad powerband and a peak figure of 357 pound-feet of torque, the peak figure achieved at 6,300 rpm.

The barking V6 put his 370Z closer to the factory GT3 power-to-weight numbers he’d been chasing for so many years. Initial testing showed a top speed of 145 miles an hour along Thunderhill’s front straight, and the Motec traction control needed a significant recalibration just to handle the bump in midrange grunt.

By the end of the day, Brian had lapped Thunderhill’s three-mile course in just 1:45. Not only had the new motor chopped two seconds off the previous best, but it put the Valkyrie 370Z within spitting distance of a real GT3 machine, which laps that same course just one second faster.

However, the desire to retain an atmospheric V6 resulted in a design that can only be described as extreme. As pre-season testing revealed, the semi-experimental motor had a few issues regarding oil pressure and oil temperature that will keep it from seeing any enduros in the near future. That said, the Z will still run in ST1/ES using the older, 390-horsepower motor.

“Though the oiling issues sent us back to the drawing board, we’ve stayed optimistic. These are just the realities of developing your own GT3 car. I’m confident the brains at Jim Wolf Technology will get it to work soon enough,” he declared.

As frustrating as that tease might’ve been, running several sessions with another hundred horsepower taught them a great deal. Brake temperatures went through the roof, and fuel consumption was a concern. It also got Brian wondering whether running such a highly strung powerplant was right for endurance racing.

Pondering Another Path

Though he was committed to the idea of a pure, old-fashioned, high-revving atmospheric motor from the start, a recent test with an ex-Blancpain Nissan GT-R GT3 sent Brian’s mind rocketing in a new direction.

“It was just easy to drive. It required a big team, but it started up, ran flawlessly, and turned incredibly fast times off the bat. We weren’t running with a great setup or new tires, but the GT-R put the power down without any problems. It wasn’t like any other turbo engine I’d ever driven.”

Turbocharged racing engines tempered by boost-by-engine speed and other tuning tricks produce plenty of power and put most of it to the ground thanks to a curve that is linear and driver-friendly — much like that produced by a high-revving atmospheric engine. If Brian could achieve that drivability with a turbocharged version of the VQ, turbocharging could be more of an asset than a hindrance.

Obviously, opting for forced induction would require a redesign to accommodate the additional piping and coolers, but that might be the lowest price to pay. If kept cool, a turbocharged variant would yield all the power and torque necessary, and, due to the ability to reduce the average engine speed, it might actually help lengthen the motor’s lifespan.

“I know it might not seem like it, but slapping on a set of turbos could help us reach our power-to-weight goals and improve reliability. Because the car either needs another 30-40 horsepower or 150-200 fewer pounds to reach GT3’s power-to-weight ratio, it might be easier to just take the weight penalty from all the turbo piping and coolers.”

“We need a motor that can occasionally operate outside of its very narrow optimal performance window. Why? S*** happens on the track. Debris plugs the radiator and drafting overheats the engine. We can’t run an endurance motor on a knife edge in this environment and expect to win regularly.”

Even though they’ve shown they have the raw pace, they need to be there at the end to tally up the points like they’re hoping to. If they can find a way to make the VQ last in the grueling conditions of endurance racing, they will prove that with a lot of thought, observation, and patience, the pesky privateers can take it to the big teams.