LMDh Engines: Why the Displacement Monsters Are Coming Back

(Motorsport-Total.com)—If it weren’t for the hybrid driving, you might feel like you’ve been transported back 15 years: Three of the four LMDh cars that made their GTP-class debuts at the 24 Hours of Daytona this weekend feature With large, partially turbocharged V8 engines. Only the Acura is a bit of an outsider in this regard.

Engines of the four manufacturers:
Acura ARX-06: 2.4-liter turbocharged V6
BMW M Hybrid V8: 4.0-liter turbocharged V8
Cadillac V-LMDh: 5.5L V8 naturally aspirated
Porsche 963: 4.6-liter turbocharged V8

Where does this apparent step back come from? The main reason lies in the regulations. But current trends in serial production also play a role. And last but not least, the question of what sustainability actually means.

Let’s get to the first and most important point: Regulations favor large-volume engines with a flat torque curve. Old LMP1 regulations applied: The hybrid pulls at full power, no matter what the combustion engine is doing. In the Hypercar/GTP regulations, be it LMH or LMDh, a completely different principle applies.

The performance curve is precisely defined. The more the electric motor works, the lower the power of the combustion engine. This happens electronically. However, this means that the internal combustion engine should theoretically be able to generate the same power in the lower speed range. Large gatherings can do this better than smaller gatherings.

Also, the smaller engines no longer have a weight advantage because the weight is fixed at 180kg. They should be able to generate 707 horsepower on their own. The rest of the drive train, including the pivot points, is standardized. This means that the large V8s fit better with the overall concept of the LMP2 chassis and standard components such as the transmission and plug-in hybrid (MGU).

Why BMW’s more recent DTM engine was left out

When the LMDH philosophy was first introduced three years ago, the premise was still valid that unity had to come from the chain. In the meantime this section has been secretly deleted. This made it possible for BMW, for example, to take the old DTM V8 engine (P66 / 1) as the basis for the M Hybrid V8 and couple it with a turbocharger.

“We wanted to combine three things: the DNA of the plant, what fit the regulations and what seemed realistic given the tight schedule,” says project manager Maurizio Lesciotta. So developing a completely new engine was out of the question for BMW. “Because we were building on an existing engine, we were able to save development time.”

“We came up with the biturbo V8 architecture, which we also use in our M8 road car. We knew we had to rely on turbocharging to displace the car. And that helped us achieve the performance needed.”

Ulrich Schulz, Head of Engines at BMW M Motorsport, adds: “We also got the P48 engine from the BMW M4 DTM. [2,0-Liter-Turbo aus der Class 1] and the P63 engine [4,4-Liter-V8-Turbo] Viewed from the BMW M8 GTE. But the potential reliability issues with the P48 and the high weight of the P63 spoke against it.”

When transforming the P66/1 into the P66/2, a test engine, and finally into the P66/3, the ultimate racing engine, BMW combined its expertise from the Formula 1 and Formula E eras. In this way, resources from three different motorsport programs were pooled.

Porsche also benefits from the shelves

Urs Kuratle (Head of the Motorsport LMDh factory at Porsche) answers the same question: “We had the full range of engines that could have been achieved. We had that [2,0-Liter-V4] An engine from the 919, but it wasn’t made for these regulations and it would have been very expensive.

The compact engine has been cut down for a lighter weight and less bulky build. It would not fit in the LMDH package and had to be made artificially heavier. Instead, the engine was taken from the 918 Spyder and paired with a turbo. BMW and Porsche have followed a similar path.

Stefan Moser, chief engineer for Porsche 963 Driving, explains that the Porsche 963 engine has a flat-plane crankshaft and is designed to have a very short stroke. pressure of 0.3 bar.

“The advantage: The engine retains its basic characteristics as a naturally aspirated engine and responds very directly to commands from the accelerator pedal. Relatively low boost pressure builds up quickly, and there is no turbo lag.” Impressive: in the Porsche 918 Spyder, the 9RD is not a loaded component. However, with some additional reinforcements, this task can now be taken over in the 963rd.

Sustainability in a new light

These examples show that sustainability is seen differently today. For a long time, the term was coined solely on the premise of reducing fuel consumption. However, over time, this led to an increase in the cost of aggregates, some of which used exotic materials, which became more and more complex.

Meanwhile, the savings potential is so small that it is no longer proportional to the costs. Example: With the LMP1 generation from 2014, fuel consumption in the 24 Hours of Le Mans race has decreased by 30 percent compared to 2013. An additional 30 percent reduction would now cost several times more.

The use of sustainable fuels pushed the issue of fuel consumption to the background anyway. Sustainability is now considered holistically: a powerful engine that consumes maybe a few percent more but doesn’t have to be developed at great cost and doesn’t use exotic raw materials suddenly seems very sustainable with environmentally friendly fuels.

Ulrich Schulz (BMW): “It’s a huge advantage that we were able to use existing materials such as steel and aluminum – both for the engine base and for individual components such as shafts, housings and other small parts. A lot of money. This is sustainable and efficient.”

This overall kind of sustainability is also given more attention in the rest of the regulations: today, no car manufacturer in the world has to prove that it can get ten more horsepower from a given cubic capacity than anyone else. All manufacturers now have the knowledge anyway. Hence the given force curve.

Also, manufacturers no longer have to prove they can build a superior chassis. Ergo, identical parts became increasingly popular in the 2010s. Today they are based on the standard LMP2 chassis. And no car ever gets custom-designed tires anymore, which makes thousands and thousands of test kilometers with disposable tires superfluous. Standard tires announced.

Naturally Aspirated V8: The American Way

Downsizing is also not a problem in the auto industry. In the latest version with the introduction of the WLTP cycle, the advantages of small turbocharged engines are gone. The advantages that these engines have in the part-load range cannot be exploited in motorsport anyway. At full load, the old principle applies: turbo, turbo drinks.

Cadillac could also come up with an architecture that no one would have predicted just a few years ago: The naturally aspirated 5.5-liter crossover V8 will make the hearts of motorsports enthusiasts beat faster in the years to come. The most American GTP is also the result of time pressure.

“Like everyone else, we didn’t have time to make a decision. We drew heavily on decades of motorsports experience with GM, especially in the eight-cylinder segment,” says GM Motorsport Director Laura Wontrop Klauser.

“We did packaging studies for a variety of engines as quickly as we could. Then we looked at the performance requirements. Based on our experience, it made sense to go ahead with the V8 engineering.”

The LMC55R is a new development that does not reinvent the wheel, but is primarily based on the DPi engine. Here, too, the focus was on cost-effectiveness. “We don’t regret anything, especially since we will also be competing in the WEC. I think we will represent America loud and strong with our car. We are proud of that.”

Why does the Acura swim upstream?

The big exception, as mentioned, is the Acura. Honda Performance Development (HPD) also capitalized on the idea of ​​efficiency, but in a different way: LMDh engine development was integrated with the IndyCar unit.

Meanwhile, IndyCar has discontinued the 2.4-liter engines and will stay with the existing 2.2-liter units for the time being. But HPD at least didn’t totally screw up development costs: A turbocharged V6 engine designed for five-digit speeds was used in the Acura ARX-06.

But why was the switch to a new concept at all? With the AR35TT, HPD had a motor in its core features [als HR28TT] From 2011. “It would have been easy to take the DPi drive and put it into our LMDh system. But that’s not how we do it,” says David Salters, president of HPD.

Of course, when the engine decision was made in early 2021 (according to Salters on January 2nd!), HPD had no way of knowing that the IndyCar engine would be discontinued. But by the time the decision was made, development had progressed so far that the “point of no return” had long been passed.

“We’re in so many racing series. It would be stupid if we didn’t create synergy there. We might be crazy, but we’re not that crazy. There are similarities. It starts with that, but then [die Projekte] Regardless because the field of application is changing. HPD has been around for 30 years. Of course, a lot of knowledge went into the development.”

“Some things have to [für das jeweilige Projekt] be determined. After all, a 24-hour race is like five Grand Prix in a row. Our mission was to build the best possible engine for the future of motorsport. “

An emotional aspect was also brought into the development: “This may be the last combustion engine we develop for motorsport. I don’t know. I said to our boys and girls: ‘Let’s develop as best we can, because it could be the last time we start from a blank slate.'” So we wanted to incorporate everything we’ve learned in our history into this product.”

“We took a big risk,” he admits. “We gave our boys and girls total freedom with the packaging. We found the best packaging possible for our engine and we are very proud of it.” The relatively small engine had to be adapted to the infrastructure, which could also accommodate larger engines.

That leaves Lamborghini and Alpine, which will launch in 2024. While Lamborghini recently opted for a V8 turbo, Alpine hasn’t reported the engine issue—and nothing has been leaked yet. The LMDH will be presented on February 6th.

By the way, Urs Kuratle was amazed at the end of the media tour: “It’s very interesting to hear that we all discussed the same questions internally. But we came up with completely different solutions. Why did we all find such different answers? We should definitely sit down and talk about it!