Stepping Up The Game

Brian Lock, a man who lives and breathes Nissan Motorsports, has built two cars, a 370Z and its sister car, an R35 GT-R, that have carried Valkyrie Autosport’s drivers to the podium for several years running.

Lock has built both these cars in his modest Santa Cruz shop with some help from Nissan, though it’s safe to say he’s been the one carrying the torch with these two former road cars. With a relatively small network to lean upon, he’s diagnosed and resolved some of the shortcomings of these two cars without having an aneurysm.

The point is that the stage was set for a serious upgrade. Brian’s reputation as a good shoe and gifted builder, particularly with Nissans, put him in touch with a racer with similar tastes. This particular racer quickly became a partner and tasked Brian with helping him set up a very special R35 GT-R.

This former Blancpain GT3 car shares the same profile, minus the aero additions, as Brian’s own homebuilt R35 GT-R, but that’s basically where the similarities end. In fact, aside from the windshield wiper assembly, unibody, and the engine block, the GT3 car has had every part replaced with a bespoke motorsports-grade piece.

It’s not just a collection of high-end bolt-ons, either. The powertrain is shifted and split to improve overall weight distribution, the suspension pickup points are altered, the track is widened, and the aerodynamic elements are so different, they completely alter the car’s character.

Fundamental Differences

Not only is the GT3 car some 700 pounds lighter than Brian’s stripped and strengthened street car, but the weight distribution, as well as the center of gravity, are shifted to help handling and traction. This begins with the relocation of the flywheel assembly. The flywheel, normally mounted to the engine, is bolted to the Xtrac transaxle in the rear. This transaxle is smaller and lighter, runs cooler, and offers much crisper shifts than the stock unit.

The flywheel relocation allows the engine to sit lower, and a recessed firewall means the motor sits farther back. The end result is a 3 percent shift, reducing the front’s weight from 56 percent to 53 percent. This may not sound like much, but it makes an enormous difference when braking and cornering.

Complemented by increased spring rate and anti-dive to keep the platform level more of the time, the additional weight at the rear axle allows the brake distribution to be spread more evenly between both axles. The street car’s front axle is responsible for 64 percent of the braking force, whereas the GT3’s front axle only takes 54 percent. Not only does this improve trail-braking, but it helps keep the front brakes cooler.

Though points for power go to Lock’s production-based GT-R, the weight difference between the two mean their straight-line speeds are similar. Outputting something near 500 horsepower and 500 pound-feet of torque, the GT3 car is not lacking much, and its delivery is improved through an interesting mapping feature: boost-by-throttle position. The result is that the motor is much more flexible, and it seldom spins the driven wheels — only the rears in the case of the GT3. “At times, you have to remind yourself you’re driving a turbo car!” Lock added.

Its incredible traction also can be attributed to a totally different suspension design. For starters, none of the suspension pickup points are shared, aside from those on the engine and unibody. The control arms are weapons-grade, too. The fronts are made from billet aluminum and the rear from tubular steel.

The pickup points are different, as is the fundamental suspension design. The stock front is a modified double wishbone and a multi-link arrangement in the rear. The GT3 car has double wishbones at all four corners. The advantages of this design are that toe settings do not change throughout the entire range of suspension travel, and that the camber settings only change in a favorable way.

Lock’s homebuilt car’s suspension is good enough to keep the settings relatively stable within a limited range of suspension movement. Once outside that, whether it be under compression or extension, the rapid changes in toe and camber causes the shape of the footprint to change.

The Role of Aerodynamics 

While the changes in suspension give the driver a greater sense of confidence, the mechanical elements are dwarfed by the aerodynamics in their contribution to the car’s overall grip. The GT3 car is, in the truest sense of the term, an “aero car.” In other words, the wings and things that protrude from the GT-R’s famously bulky shape are mainly what afford it such outstanding cornering and braking performance.

Due to the aerodynamic download and its overwhelming influence in handling, the GT3’s handling is tuned differently. The bump rubbers limit travel during high grip/high downforce situations, while the springs provide compliance in slower corners when the car is not resting on the bump rubbers.

“We’ve got two bump-stops at both ends of the front suspension. These come in several different durometers, and depending on how you stack them, you choose between a progressive rate or a fixed rate,” Lock explained.

Picking the right bump stops makes the biggest changes in compliance. They also require the removal of the shock to alter. For quick changes or fine-tuning, there are the packers to pick from. These packers are quick-change delrin shims that clip over the damper shaft.

Taking a Stab

The first test, done at Sonoma, was startling. The car was basically running for the first time after sitting in a container for a few years. No suspension adjustments, no wing tweaking, just new fluids were enough to help him lap the car in the 1:38s. Considering the last event it ran was the Nurburgring, a much bumpier track, that time is remarkable.

The fact it ran all day without a hiccup was even more impressive than its initial pace. For a heavy car with a turbo motor, it’s sort of incredible how well it managed heat. Nothing cooked, which was quite a departure from the street car. In fact, Lock realized he needed to tape off a few inlets to reach operating temperatures in the brisk spring weather.

As he learned, choosing the wrong bumpers and packers can keep the car from producing consistent downforce during fast direction changes. Too much roll and pitch prevented steady airflow over the splitter. The resulting hopping at the front end limited his pace through the Esses.

Unfortunately, supply chain hangups delayed delivery of those rubbers and packers, and he had to return to Sonoma for the second test without any new parts. At least he’d done his homework beforehand and could start sorting out the pronounced understeer, which limited the car’s potential a couple of weeks earlier.

The week before, Lock scoured through the GT3 car’s 500-page manual. “I spent a few nights reading through the CFD stats and I was blown away. The amount of data is hard to process. Among other things, it lists a specific amount of downforce and drag at different ride heights, spanning from 35 to 80 millimeters in five-millimeter increments.”

Surprisingly, lowering the nose by 15mm  had the effect of turning frustrating understeer into frightening oversteer. “We gained another 50 percent downforce with that change, but then the car was nearly undrivable,” Lock said. “We had to raise the nose a little to strike a happy balance.

“The optimal ride height for aero balance wasn’t something I could pursue at that stage, because the front kept smacking against the ground.”

Because they didn’t have any more packers, their “packer gap,” i.e. the amount of travel before bump rubber engagement, was too long.

Though he’s been aided by the manual, this approach to tuning a car is a little confusing. Perhaps the hardest diagnosis to make involves distinguishing between an aerodynamic issue and a mechanical issue. Because aerodynamic changes make a massive impact on the car’s balance, it’s possible that one can mask a mechanical issue without understanding the full impact of such a change. Too much grip may minimize oversteer, but often at the expense of straight-line speed.

What Lock has been able to determine is that setting up a car like this begins with picking the right ride heights, which is determined by the track’s surface quality, and then finding the best compromise between drag and downforce, which is determined by the length of the straightaways as well as the aerodynamic setup. For their Sonoma test, they were playing with greater downforce, greater drag settings.

“The difference in the data is pretty obvious,” Lock said. “The GT3’s cornering speeds are higher and the braking distances are shorter, but that also comes with a setback: it runs into a wall at the end of straights; we’re usually down 4-5 miles per hour.”

Translation: Black and Blue

As if the challenge of setting up this aero car weren’t hard enough, Brian had to contend with the physical demands that keep most GT3 drivers in the gym a couple hours a day. The extra grip means its more physically demanding machine than the street car could ever hope to be. Regularly pulling 2 g’s takes a toll on the driver, and Brian admits it’s a little too much for him at the moment.

Thankfully, the car offers some minor comforts. There’s power steering, great ergonomics, and an air-conditioning system blows cold through four ducts: two on the dash, one in the back of the seat, and one adjustable unit that can be placed just about anywhere. Even so, it only took about eight laps before he was panting.

“In the street car, my arms feel heavy after a two-hour stint. After half a session in the GT3, I’m done!” he laughed. Difficulty keeping his legs in place is a testament to the cornering forces this car exerts on its driver, and he plans to pour a snugger seat to help keep his lower half in one place.

Thankfully, his energy does not need to be spent diagnosing gremlins or worrying about what might break. “As a builder-driver, this is a whole new experience. It’s liberating! Racing is way more fun when all you do is focus on driving and setup!”

There aren’t too many additions they must make to the car at this stage, but they still feel like they’ve got some way to go, despite having learned a great deal. Along with a rear view camera, a new radio, and a budget telemetry system, it needs a specific alignment and the right packers and bump stops to get this aero-dependent machine cornering like it can. As it currently sits, it’s capable of 1:34 laps.

Ride along in the GT3 Nissan GT-R at WeatherTech Raceway Laguna Seca.

“We feel like we have made great strides in setup, but we want to accelerate the pace,” Lock said. “We contacted 057 Motorsports Consulting for chassis help as we’ve recognized our limitations at this stage. After all, there is a reason most professional teams have engineers on staff.

“The goal right now is to see if we can get this rare car up to speed against its GT3 counterparts that run regularly in SRO GT World Challenge. If we can get the car sorted out, and both drivers stick to their workout regimens, we might look at trying to enter a race or two.

Valkyrie’s humble roots and beginnings may, with a little luck, soon leave the world of club racing and enter a new arena filled with some of the fastest GT cars in the world.