Setting up a Nissan GTR up for racing the 25 Hours of Thunderhill was going to be different from building one time attack. Valkyrie Autosport’s Brian Lock understood that early on, and building a GTR for endurance racing is also something of a lonely pursuit. Because of the price of the car — new or used — not a lot of them have been converted for racing. Most of them sit in climate-controlled garages under car covers with a high thread count.
A time attack car is all about that one fast lap, so you essentially can address the problem with obscene amounts of horsepower and massive tires, which is something the GTR can deliver. For racing, specifically endurance racing where power output has been curtailed for reliability, cornering speeds become more important.
“Any setup info that might be out there is either going to be totally wrong for a restricted power setup or it’s going to be just not well developed,” said Brian Lock, owner of Valkyrie Autosport. “Even if there has obviously been some very capable teams that have made some monster time attack cars, a lot of that setup data is going to be pretty much useless for our effort with the car.
Weight Reduction
Part of Valkyrie’s efforts focused on reducing the weight of the all-wheel-drive car. In factory trim, the GTR’s curb weight is right around 3,900 pounds. Lock replaced the factory hood, doors and rear deck lid with dry carbon parts. Eventually he was even able to get the FIA GT3 carbon quarter panels, fenders and bumpers to help reduce mass. Even so, with the addition of the roll cage, safety equipment a 44-gallon fuel cell and endurance lighting, the GTR still trims out at an immodest 3,600 pounds with the driver. Considering the factory weight is measured without a driver, total weight reduction was not quite 400 pounds.
“You’d think it would be lighter than that, but she’s still a big girl,” Lock said. With the final weight determined, the team began suspension development.
Suspension
Because of the relationship NASA and Valkyrie had with Motion Control Systems and Hyperco because of the development work on the NP01 and NP01-EVO, the two companies were a logical choice.
“We knew that there was going to be a development curve for sure,” Lock said. “We wanted to go with a shock manufacturer that we would be able to work with and go back and forth and send the shocks back for lengthening, or shortening, or re-valving, whatever the case may be. Which we ended up doing several times with MCS to get things just right.”
Interestingly enough, part of that development work focused on controlling droop because of its negative effects on the speed of tire changes in the hot pits. As is widely known, most of the GTR’s OE components were rock solid. But they were developed for street use and lacked the adjustability Valkyrie needed to achieve the cornering speeds it was looking for. Also, because the factory bushings were rubber, they had to go.
“It’s absolutely crucial on a 3,500 pound racecar with 600 horsepower and 13 inch wide tires,” Lock said. “Because the forces that you’re putting through those rubber bushings, they were never ever intended for. And it’s not so much that they’re going to fail, but even if they don’t, we align these cars to within 16ths of an inch, if not less. And you would have probably a half inch to an inch of deflection in these bushings. So you’d have some dynamic alignment changes.”
That’s where suspension components from NISMO and SPL came into play. In the rear, the team replaced the lower control arms, sway bar end links and then replaced the factory rubber bushings in the factory knuckle and upper control arm with spherical bearings. At the front, the team retained the factory front lower control arm with the added spherical bearings and changed the end links and upper control arms with pieces from SPL.
“Any factory piece that does remain factory — knuckles, factory rear upper control arm, factory front lower control arm — all of the OE rubber bushings have been pressed out and SPL spherical bearings have been pressed in,” Lock said.
Another part of the challenge was the team changed its approach midcourse, so to speak. They had been developing the car for ST3/E0 competition on Toyo RR tires, but made the decision to pursue ST1/ES trim and to use Toyo RS1 slicks. The team added downforce thanks to the CFD body panels and aero bits. Those changes created a lot more development challenges for the team.
“Pretty much every time we ran the car after that transition, which was actually halfway through 2019, we were changing spring rates every single time we went to the track. We were going up and up and up and up trying to handle the extra cornering loads with the wider tires we put on,” Lock said. “And then we also moved to a Toyo RS1 as opposed to the RR. So not only were we dealing with additional loads from a wider stickier tire, but then obviously now we were talking about downforce. And the fun part about when you’re talking about real levels of downforce is you start to need a heck of a lot of spring just to keep the chassis off the ground at high speed. But then you start running into issues with mechanical grip at low speed. So we started diving into the deep end with that. And to be honest, the development is not near done with the car in that regard.”
Braking
Obviously, if you can’t trail-brake a car properly, it is never going to be fast. One of the issues Valkyrie had early on was, as highly developed as the car is, they were trying to make the original equipment ABS and Brembo hydraulics work on aggressive, racing setup.
Again, from relationships that stemmed from the NASA Prototype, Valkyrie turned to StopTech, which helped them find calipers and pistons sized appropriately to work with all the mechanical and aerodynamic grip without going into “ice mode.” Budget was a concern, so they were trying to keep much of the OEM equipment intact.
“Most OE cars in some form or another suffers from the dreaded ice mode or crash mode where you’re so far outside of the program algorithm, whether it be stopping rate, or G-forces, or one tire slowing down at an excessive rate as opposed to another when you’re, let’s say, trail braking and the tire’s trying to lock,” Lock said. “The system wants to freak out on you and go into an error mode.”
Finding the caliper piston size suitable for the car also meant developing the system with an eye toward driver feedback. A pedal that was too touchy or stiff or difficult to get used to wouldn’t work on an enduro car driven by lots of different drivers of varying talent and experience.
There’s more to the story of the development of the car, and we’ll get to that in future installments, but the team’s efforts were sufficient enough to net them the ES class win and a top five finish at the 2019 25 Hours of Thunderhill.
“We were basically racing it and developing at the same time. We didn’t have the budget to do too much private testing,” Lock said. “Anytime the car was running, our clients had to be behind the wheel writing the cheque. I would say we did … I can’t think of one test day other than the initial shakedown of the car that we did without a client there helping to pay the bills.”
