Ever since the rise of sporty prototype racing cars in the late 1960s, it feels like we’re doomed to repeat history. Cars are either regulated for being too fast and/or for purely political reasons, or manufacturers are priced for trying to outdo each other, leading to empty grids.

Five-liter monsters like the Porsche 917 and Ferrari 512, with their 5.0-liter engines, were (rightly) deemed too fast in the early 70s. engine regulations relatively open to an expensive F1-like formula in the early 90s. The GT1 was canceled by Porsche, Toyota and Mercedes, all of which were building increasingly expensive cars that expanded the definition of “road car” “. The LMP1 was shot down by cars that required F1-level budgets, in exchange for far less marketing value.

LMDh seeks not to repeat old mistakes. First announced at Daytona in 2020, LMDh is a joint creation of IMSA and ACO, the governing body of the 24 Hours of Le Mans, designed as a relatively low-cost platform for automakers to build a car to participate in the IMSA WeatherTech series. and the FIA ​​World Endurance Championship. This means an automaker can build a car to battle for overall wins at Daytona, Sebring and Le Mans. And to ensure automakers stick around for the long haul, IMSA and ACO are encouraging something new: partnership and transparency.

“In the case of a collaboration between all the equipment manufacturers, the technical partners on the hybrid engine side, Michelin tire partner, it is the only way, I think, to finally arrive at the presentation in the first race of this new platform. in 2023, everyone working together,” says IMSA President John Doonan in an interview with Road & Track. “When this race starts, it’s every OEM for themselves, and they’ll come out and put on an amazing show. But to get us to the starting point, it’s been a very genuine level of communication between everyone to get together. ensure that collectively as a sport we get to the right place, reliably so the cars can go out and perform.”

The LMDh regulation takes the current IMSA DPi formula as its starting point. As with DPi, LMDh cars are based on a chassis made by Dallara, Oreca, Multimatic or Ligier, with bodywork, aerodynamics and engine supplied by an OEM. The big difference is starting the engine rearward, with all LMDh cars sharing a common hybrid system with batteries supplied by Williams Advanced Engineering, an engine from Bosch and a transaxle from XTrac. The tires are from Michelin. Power is limited to 671 hp at the rear wheels, while minimum weight is 2270 pounds. Dimensions are also defined, with a maximum length of 16.7 feet, a maximum width of 6.5 feet and a wheelbase of 10.3 feet. Underfloor aerodynamics are regulated, although OEMs have freedom with the bodywork, and therefore, the aero on the car.

Looking ahead to the LMDh cars’ debut at the Rolex 24 at Daytona next year – where they will race in IMSA’s GTP class, named after its much-loved ’80s prototype class – all parties are talking to each other. This includes car manufacturers, who attend regular meetings organized by IMSA and ACO. It’s unusual in motorsport, but necessary to ensure that all common hybrid components work as expected next season. OEMs should also report any planned test dates to the working group. Any LMDh registration must also be subjected to wind tunnel testing by IMSA and/or the ACO.

In his previous role as head of Mazda Motorsports, Doonan attended meetings in 2018 and 2019 for what he calls “DPi 2.0”. The partnership with the ACO came a little later and was a game-changer.

“IMSA was considering a hybrid with the next-generation DPi,” says Matt Kurdock, IMSA’s CTO. But a hybrid system was difficult to fit into the current LMP2 chassis that underpins the DPi cars. “Working with the ACO, we discovered that we could unify and build a new platform. It’s a monocoque designed around the survival cell where the battery enters from the bottom. The convergence between the IMSA and the ACO was necessary for this to happen.”

Having a car that can compete in the IMSA WeatherTech series and the WEC – and therefore the “triple crown” of endurance racing, Daytona, Sebring and Le Mans – has made LMDh viable. It’s better for OEMs, who want to race at the highest level but don’t want to spend exorbitant sums to do so; hybrid system suppliers and Michelin, which will have more customers; chassis builders, who can afford the expense and complexity of building a new hybrid-ready chassis; and all the promoters, who will have more prototypes in the race.

A teaser of Cadillac’s LMDh competitor.


Doonan frequently repeats that old adage, “the market will speak.” To that end, the two current DPi automakers, Acura and Cadillac, have committed to racing LMDh next year, with Porsche and BMW also set to join. Alpine will have an LMDh car competing in 2024, and while Audi has reportedly canceled its program, Lamborghini is expected to announce its entry for 2024 in the near future.

“Cost sustainability is key and relevance is key, especially as motorsport is a major marketing platform for manufacturers,” says Kurdock. “That’s what this set of regulations is intended to do – not just to deliver a cost-effective overall specification that includes hybrid, but to do so in a cost-controlled way, which to date, at least in sports car racing, is unprecedented.”

OEMs must also notify the task force of any planned private test dates, and in October IMSA will hold a “sanction test” at Road America after Petit Le Mans for all LMDh cars aiming to compete next year. “It’s officially organized by IMSA or ACO or the collective, [and] it puts us in a place to collect data, monitor demonstrated performance,” says Doonan. Further testing will take place before Daytona next year, and LMDh cars that will compete in the IMSA WeatherTech Series need to be taken to the wind tunnel. Windshear in Charlotte for aerodynamics Cars participating in the WEC will be evaluated at the Sauber wind tunnel in Switzerland.

bmw lmdh
A sketch of BMW’s LMDh car.


It is important for IMSA and the ACO to have this data, not only so that there is fair competition between LMDh cars of different brands, but also so that they can be compared with LMH prototypes carrying the same name but quite different. Le Mans Hypercar (LMH) was created by the ACO and FIA to replace LMP1 following the departures of Audi and Porsche. LMH cars have chassis that are not made by external suppliers, with the possibility of using a hybrid system on the front axle. Toyota has been competing with a hybrid Hypercar so far, with Peugeot set to join the grid later this year and Ferrari following next year. American team Glickenhaus is running a non-hybrid hypercar in the WEC, and privateer ByKolles aims to do the same with a car named after Vanwall. At next year’s World Endurance Championship, LMH and LMDh cars will face off, and while LMH cars are invited to compete in the IMSA WeatherTech Series, no entries have yet been announced, although the Peugeot 9×8 could come to the United States as, hilariously, a dodge. The idea is for the LMH and LMDh cars to go around Le Mans in around 3h30. “Whether it’s tire choice, whether it’s aero testing…whether it’s four-wheel drive activation speeds, I think we’re able to monitor the cars so they can compete fairly. .”

Still, OEMs have some freedom with the internal combustion engine in particular. According to a Porsche press release from earlier this year, the engine has a minimum weight of 180 kg (396.8 pounds), a rev limit of 10,000 rpm and it must not be louder than 110 decibels. .

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But it doesn’t have to be production-based. “We have restrictions on the maximum engine length, and that’s to protect the packaging of the hybrid system,” says Kudrock. “Maximum engine length of 640mm, we have a minimum crankshaft height, we have a minimum weight. So basically you can bring a very bespoke product, but you might have to bolt some ballast on it, you may have to -be making compromises.”

LMH and LMDh cars will be limited to 644 to 697 hp at the wheels, depending on the balance of performance, and that includes both the engine and the hybrid system. Kurdock hinted that it could be up to manufacturers to go with a production-based engine, as in LMDh the hybrid system can be used to bridge any gap between ICE output and maximum power allowed at the wheels. “You don’t necessarily have to bring in a custom race engine, a very powerful race engine. You can bring in a production engine and use some of the hybrid system to bridge that power gap and hit the target. That’s what the hybrid system is designed to do.”

The hybrid system is designed to deliver continuous power output, although OEMs can deploy the extra power as they wish. Still, it looks like Porsche is doing something interesting with its ICE – test drive videos of the car reveal something that looks a lot like a flat V-8.

There is a lot of work to be done between now and this first sanction test. The OEMs will conduct private testing, build infrastructure, finalize driver rosters and sell cars to customer teams. The exact specifications of the hybrid system are also being finalized. But once the green flag flies at Daytona next January, the hope is that all this collaboration will give way to fierce competition between many automakers for years to come.

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