The return of GTP racing to IMSA gets a big thumbs-up from fans – Ars Technica

The crowd streamed onto the track before the race, seizing their last chance to see the brightly liveried cars up close. Daytona had been busy in January, but the crowd at Road Atlanta seemed even larger. To be honest, though, the race the fans were here to see would not be one for the ages. A 52-car grid packed into just 2.8 miles of race track promised potential trouble, and the 10-hour race saw 14 interruptions by the safety car, never getting into a rhythm. But I’m not sure that mattered much; the main draw for many in attendance that Saturday was simply seeing this new era of hybrid prototypes in person, and on that score, everyone left with smiles.

We’ve spilled plenty of pixels over the past 18 months or so delving into some of the minutiae of this new class of racing car, variously known as LMDh or GTP. Briefly, these are purpose-built racing cars, which start with a carbon-fiber spine from one of four racecar constructors and then add an engine, bodywork, and software from one of the four OEMs that participate, and then the same Xtrac gearbox, Williams Advanced Engineering lithium-ion battery, and Bosch electric motor as a way to keep development costs reasonable.

The rules purposely limit the amount of aerodynamic downforce a car can generate relative to the amount of drag it creates, and they positively encourage each car maker to give these race cars styling that calls out to their road-going products.

It appears to have worked. The designs resonated, particularly Cadillac’s, which graces bags of Doritos and the cover of the latest Forza Motorsport game. It might have looked even better with a Corvette badge and an all-yellow paint job (though that’s a view that doesn’t endear me to GM).

The Porsches looked best head-on. As it crested the rise and built up speed on the back straight at Road Atlanta—or as it dashed down the Mulsanne straight at Le Mans—the 963 intentionally evoked the legendary 962. Better yet, Porsche brought variety: a pair of customer 963s and a pair run by Penske Racing. The cars were driven by big-name drivers, too—Indy 500 winner and champion Josef Newgarden was the third driver for one of the Penske Porsches, and F1’s 2009 World Champion Jenson Button was aboard the flat-yellow JDC car.

BMW’s V8 M Hybrid was unmistakable for anything else, particularly at night, with its illuminated kidney grilles. I’ll be honest: I see less of a link between Acura’s road cars and its ARX-06, but there’s no denying that car’s outright speed.

None were as nice to look at as the Ferrari 499P, which won Le Mans earlier this year. That car is built to a different set of rules (called LMH), but IMSA and the World Endurance Championship have a process to balance performance between the two so they can compete together. (None of the GTP teams that also compete in WEC are particularly happy with that performance balancing, which seemed to favor the Ferrari and Toyota LMH cars this season.)

I ran into Ferdinando Canizzo, technical director of Ferrari Competitzione GT and technical boss for the 499P program, shortly before the green flag and asked him whether we’d see the Ferrari prototype race in IMSA next year.

His reply: “Can you see any reason why we shouldn’t bring it here?”

“I hope so. That’s the whole idea of convergence,” said IMSA President John Doonan when I quizzed him on the possibility of a Ferrari prototype showing up in 2024. The first step would be for a 499P to visit North Carolina’s Windshear wind tunnel and the IMSA R&D center for homologation.

“I think on LMDh, the ruleset is so tight and the expectations are very clear, both for the manufacturer and for us,” Doonan said. “LMH obviously has a little more freedom in their ruleset. So we’ve just got to continue to figure out ways to balance the two, but we’re very open to those manufacturers coming.” Indeed, in 2025, the Aston Martin Valkyrie—built to LMH rules—is due to race in IMSA, and the series will add Lamborghini (with an LMDh-based car) next year.

The cars all look and sound different, but the racing is close. The rules allow a maximum of 670 hp (500 kW) at the rear wheels, policed by torque sensors. Up to 67 hp (50 kW) of that comes from the Bosch electric motor, often filling holes or troughs in the internal combustion engine’s torque curve, then regenerating power from the rear axle under braking.

Those torque sensors report any violations to Race Control, where a team of officials monitor the race via a wall of screens and coordinate with the trackside marshals. Before a new make of car is allowed to compete in GTP, in advance of the start of the season, it goes into the Windshear wind tunnel in North Carolina to have its aerodynamics benchmarked. Then IMSA Senior Director of Race Operations Mark Raffauf and his team spend the next few days taking it to pieces and putting it back together again to make sure it conforms to the regulations.

“In the ’80s in GTP—the first generation of GTP—the rules were ‘if it didn’t say you couldn’t, you could.’ Today, it’s the exact opposite. If it doesn’t say you can, you can’t,” Raffauf told Ars.

“Nowadays, the cars are way different—not just safer, but more technically capable of handling so many different kinds of situations, whether it’s the mechanical or the performance side or the safety side,” he said. “In the old days, you went to Daytona, you’d qualify at a [lap]time, but you’d race five seconds slower because if you ran that time, the car would fall apart. Even the best, the [Porsche] 962s, you could not race them. These things? You can race them 24 hours flat out. You have to. So it’s a big difference, but it’s more complicated.”

In the lead-up to the start of the season in January, reliability—or the potential lack of it—was high on everyone’s mind. Porsche and the Penske team had the job of being the first to integrate the hybrid components with their new race car, logging tens of thousands of miles in testing in the process. It was developed during the supply chain chaos amid the pandemic, when spare parts were in short supply. But mechanical reliability has surprised the doubters; a BMW and a Porsche each needed lengthy pit stops at Daytona to change their hybrid battery, but I can’t remember another such occasion for the rest of the season.

Not everyone doubted, however. “From the first test that we went out with, we were really shocked by the build quality and the reliability that we have in that car. So I’m not too surprised by where our reliability is at this point,” said Kalvin Parker, assistant program manager at Cadillac Racing. “I think we’ve been chasing the same issues that everybody else has been chasing. We’ve seen our competitors definitely grow and develop more robust cars throughout the competition. But I’ve been pretty confident with what we’ve had since the beginning,” Parker said.

“The time for the development was… the shortest and most packed one [for BMW] and was quite tough for everybody… but we managed to have the cars ready in Daytona. As you said, it was a tough race, but for us, the biggest goal was to have two cars there and finish the race with two cars. We managed this, and at the end, we were quite happy,” said Andreas Roos, head of BMW M Motorsport.

“Still, we saw that at Daytona we were behind the other OEMs, which was expected for us,” Roos continued. “But every team or every manufacturer was not ready in Daytona, so everybody’s still had to develop, and was able to develop, and when you are a bit behind and you’re on the back foot, you always have to do a bigger step than the others in the development. But I think we manage this quite well.”

Although the cars’ mechanical and aerodynamic specifications are fixed after homologation, there has been plenty for the team to learn about in terms of suspension setups as well as software iterations. Even Porsche, with all those testing miles, learned a lot throughout 2023.

“At the start of the year, when we entered the championship, we focused so much on the components of the car and developing those and not so much on setup development,” said Matt Campbell, one of the Porsche Penske drivers. “So as we’ve gone through the year, we’ve really worked on setup development. Really, I suppose post-Sebring and Long Beach onward, this has been a rapid rise, and we’re still learning now. But more or less from the middle of the year onward has been really focused on software, and that’s where we found a lot of gains.”

The Porsche Penske team and the Chip Ganassi Cadillac team are both competing in the World Endurance Championship, as well as in IMSA, which Campbell said has helped his team in the development race “because from one weekend to the next, in between both series, we’re bringing something new to the car for us.”

The championship remained tight throughout the 2023 season, and going into Petit Le Mans, it was almost neck and neck between the WTR Acura, a Cadillac run by Action Express Racing, and one of the Penske Porsches, with the other Penske, a BMW, and the second Acura (run this year by Meyer Shank Racing) still in mathematical contention. So the pace of development had to be kept up all year.

“We showed up here with a fully new software for this weekend and how we use a lot of the hybrid stuff—we’re constantly figuring out ways to use it better,” explained Ricky Taylor, a driver with the Wayne Taylor Racing team, which ran one Acura this year and will expand to a pair in 2024. “The main performance advantage comes on the regen[erative braking] side… keeping the state of charge in a range that’s not going to damage the battery, so I’m never going to zero, never going to 100. And then if you get close to that limit, you lose regen, or if you get lower on the limit, you can’t deploy,” Taylor said.

The digital complexity of the GTP cars means dozens of engineers working away in the shadows on software updates and the like, but it also translates to a high mental workload in the car for the drivers. “Depending on the request from the engineers, there’s quite a lot going on,” said Louis Deletraz, one of Taylor’s two co-drivers for the race.

The steering wheels are covered in multifunction dials and buttons, which allow a driver to adjust things like brake balance, the amount of regen braking, how the rear differential locks, and more. “We used to start a race with a balance and you had to keep it the whole way, whereas now we can adapt driver by driver and change the balance quite a lot—much more than I would have expected,” said Deletraz, who spent most of this year racing the lighter, less powerful, less complicated (and not hybrid) LMP2 prototype class in WEC.

Deletraz was the third driver for the WTR team, racing at just the longer endurance events on the calendar. For other drivers, it was their first time in the car. “The first 15 laps I was like, OK, this has taken a bit longer than I thought to get used to the car, the track—never been to the track before, either. And then it clicked, and it felt natural. We made setup changes; I could feel them,” said Jenson Button.

GTP cars produce less downforce than the DPi prototypes they replaced, and they weigh a lot more. More than one driver has told me that in addition to looking like a cross between a GT and a prototype, they drive somewhere between the two as well. Button had less time for that idea.

“We’re still 10 seconds quicker than a GT car. When you go through turn three to five, it’s unbelievably quick, and you have to be very precise,” he told me. “It’s more difficult to be precise because there’s not as much downforce, so you turn in before the corner, hoping that you’ve judged it right, whether it’s being as precise as you would like. And I heard the same thing. I had a lot of drivers having positive and negative things to say about the cars. So I was a bit skeptical, but after driving it for a day, it’s a racing car. With downforce.”

“You’re not gonna like some things; you’re gonna like other things. It locks up when you’re going slow because it has mechanical grip that these cars don’t have,” Button said. “So you’re always fighting the same thing as you are in an F1 car. It’s just that you’re going slower with a bit less downforce. So mechanically, these cars don’t have a lot of grip, and you’re running as stiff as you can so that you get the car as low as you can to get the downforce to actually work. If it’s in the air, you might get the car soft, and it’s compliant in low-speed corners, but you’re useless in high-speed corners. It’s that fight you’re always having with the downforce and the mechanical grip.”

I won’t spoil the actual race outcome here—IMSA has uploaded the entire 10 hours on YouTube now, so you can decide whether 14 cautions might be a little too many for this challenging race. I’ll also hold off on declaring this the start of a new golden era for endurance racing—the last time I did that, with regard to the epic (and epically expensive) LMP1 hybrids, Audi and Porsche ended their programs within a year, leaving just Toyota.

But it’s hard not to be enthusiastic.