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Racecar Engineering

THE VAST AND THE FURIOUS

You can always rely on BMW to be different and while its rivals campaign regular sports and GT cars its GTE weapon of choice is the gargantuan M8

The four months of lost time put the team under immense pressure, and perhaps compromised the ultimate set-up for the car


BMW’s history with endurance racing has been somewhat chequered in the last 20 years in that, while it won the 1999 Le Mans 24 hours overall with the V12 LMR, one of the best-looking prototype racecars the world has seen, in GT racing the picture has been more complex.

From the M3 GT2, featuring a 4-litre V8 engine which did not exist in true production form, to its new car, the M8, which is based on the 7 Series executive saloon, the firm has often not had a car that fits with the traditional GT philosophy along the same lines as Ferrari, Porsche, Aston Martin or Corvette, with their sportscar derived racers. So it has consistently required the agreement of rival manufacturers to be given waivers to race – and the brand new M8 GTE is no exception.

Unveiled in road car spec at the Frankfurt Show in October, 2017, the base car for BMW’s new racer is huge. But that size has almost proven to be its undoing, as major changes were required to the racecar, demanded by the FIA and the ACO after consultation with rival manufacturers, before it could even start to consider balancing its performance against its sportscar-fielding rivals.

By that October launch, of course, the car had already undergone some extensive test and development work, starting in early July at Germany’s Dingolfing test track. There were some issues early on in the testing, with the flat crank engine causing vibrations that needed to be solved before proper testing could begin in earnest, but the biggest challenge, as usual, came from BMW’s competitors, who were required to agree to the base concept. They left it as late as possible to do so, and cost BMW an estimated four months of development time.


The programme for the M8 is as large as the car itself. Two cars are entered into the full IMSA WeatherTech Sportscar Championship that started in January at Daytona, Florida, and there is a two-car entry in the FIA World Endurance Championship’s so-called ‘Super Season’, that starts in May at Spa and runs through to the Le Mans 24-hours, 2019.

There is some carry-over from the M6 GTLM that has previously run in both GT3 and GTE trim in the States, but much of the car is new. The engine, for example, is based on the 4.4-litre unit used last season in the M6, but with reduced capacity to four litres with a twin turbo layout. That meant that the company had to abandon its much-vaunted claim that 95 per cent of the race engine featured production car parts, and instead build a race-spec unit.

‘Overall, on the engine side we started with the base engine that has also run in the M6 GT and GTLM and brought that down to four litres, with full accordance to the regulations and in that respect we also went away from the 95 per cent production parts concept to 30 to 45 per cent production based,’ says BMW Motorsport director Jens Marquardt. ‘It is still based on the production engine, but with very different components involved. We also changed the crankshaft, cylinder heads and everything and worked on efficiency and power. I think that we have done a pretty decent job.’

The engine is based on the 4.4-litre unit that saw service in the M6 GTLM car last season, but capacity has been cut to 4 litres while BMW has also adopted a twin-turbo layout

M-powered

The inlet system is completely different, as are the turbos and wastegates, but the changes and the installation led to vibration issues early on in the test programme. The company admits that bits fell off the car during testing, but the official line is that this was more down to a materials issue than the engine vibration. ‘With the flat crank engine we encountered some vibration issues at an early stage that we had to address and solve,’ says Marquardt. ‘Other than [these] vibration issues, we have not encountered anything that I would consider to be a major issue. I think I have been really surprised, we have done a lot of work on the dyno.

‘We have had [the vibration] in the M3 and in the DTM car so it is nothing that is unusual. It is down to the concept of the engine,’ Marquardt adds. ‘You can do a lot of simulation, but the vibration itself is not an issue at all; you can run that engine to death on the dyno with no issue, but when you have installed it into a car and you get into resonance issues, that’s where you have to figure out, does it cause any other issues? We had much more vibration on the M3 GT2 than we have now, but they never caused natural same frequency issues. It might not be comfortable for the drivers when you are going through those resonance peaks, but it is not an issue that would hamper the performance. We handled the problem in a normal way.’

Unlike its rival Aston Martin, the engine bay is plenty big enough to house the turbocharged engine and there are no packaging dramas. ‘Our engine bay is huge, there is no issue there,’ says Marquardt with a laugh. ‘The thing about the base car, it has a pretty big front. There is a lot of space under the bonnet that isn’t used, especially as you drop the engine and move it as far back as you can. Intercooler-wise it is not an issue; cooling is not an issue.’

Power is delivered to the rear wheels through an Xtrac gearbox, the company choosing to switch from Ricardo, which continues to supply the GT3 customer car. BMW felt that the Xtrac gearbox offered ‘more potential in the current package than we had in the package in the M6,’ Marquardt says.

On balance

The M8 weighs in at 1220kg, down from an estimated base weight of 1800kg of the road car, and races at 1250kg, heavier than the previous car by regulation, while it also has smaller air restrictors on the smaller-capacity engine. BMW says that this contributed to its apparent lack of speed in the ‘ROAR before the 24’ event, and after extensive analysis, the BoP table for the race saw an increase in power, less weight, a larger fuel capacity and faster refuelling.

The M8 has had to undergo the usual balance of performance testing, at Daytona in December and January. However, IMSA started with all new cars in a conservative set-up and will need a season of running before they are able to balance the cars perfectly.

The auto BoP that will be used in the FIA WEC will cause more of an issue as there is only the test session in France in April, and the Spa 6 hours in May, to see the car in full race trim ahead of the Le Mans 24 hours in June. The FIA’s method of balancing the performance is to rely on the manufacturer to explain how much better or worse the new car will perform, and that information will form a baseline. Also available to it will be the data collected by IMSA from the Daytona and Sebring races.

The M8 has had access to BMW’s mighty resources including its huge Aerolab wind tunnel (top) but the aerodynamic effort was massively set back after a late decision by rule-makers and rivals to ask BMW to raise the ride height of the car

‘With the flat crank engine we encountered some vibration issues at an early stage that we had to address and solve’

Raising issues

Bringing such a car to GT racing has led to the usual gamesmanship from BMW’s rivals, who recognise the importance of having the name in the series while not necessarily agreeing to the base concept. BMW worked with the FIA in the early stages of development to produce a concept that would be acceptable to it in terms of the BoP, but having lowered the car to the lowest possible level, it was then required that the car be raised slightly. It was not an innocuous decision; rivals deliberately waited until the last minute, and completely compromised all the aerodynamic work that had already been conducted on the car.

‘It is the typical game,’ says Marquardt, although it is a game that clearly rankles with him as it cost time, performance and money. ‘It is competition. Our approach is to be as open as we can with everyone with the FIA, ACO and IMSA, and the other competitors. It doesn’t help anyone if you pull the rabbit out of the hat, and then the rabbit doesn’t walk. Obviously the car has a certain frontal area, and the FIA wanted us to be in a certain window so that they could balance us properly and so we made proposals, had a pre-agreement and worked towards that, and then it turned out to be not acceptable to the FIA. We had to redo it to what they said was [now] acceptable for them, and that cost four months, and a little bit of money, and that was not a small amount of work, which is why it cost us four months.’

That four months of lost time put the team under immense pressure, and perhaps compromised the ultimate set-up for the car as key decisions had to be reached quickly and without the usual analysis. ‘We have tried to be as early as we could, and obviously not everyone responded as early as they could, which is normal,’ says Marquardt. ‘With regard to the discussions, we have good ones with the FIA and ACO and everyone involved regarding calendar changes, and homologation changes; we can make our lives easier if we do a slightly different process where you get concept approval, intermediate approval and then final approval. [The current system] puts a lot of work onto the people that we are responsible for, no matter what manufacturer, and we have to keep the workload, which is already high on them, to a reasonable level. It doesn’t help if you delay things artificially and make things more difficult. It increases the workload, brings the cost up and it doesn’t make the racing any better.’

The WEC has adopted IMSA’s pit stop rules, allowing refuelling and tyre changes simultaneously; emphasising slick pit-work
The car struggled for outright pace during Daytona testing. BMW plans to field two M8s in IMSA plus another brace in WEC
Suspension is conventional double wishbone set-up with 4-way adjustable shocks front and rear. Car body is composite

Much of the early testing was conducted with an adapted M6 GTLM, which allowed the team to evaluate key components for the M8 GTE

Motive 8

BMW had not yet reached the stage of building parts for the car and so it was not all bad, but the company had to ditch all of its aero work and start again. ‘Everything that we did before went into the bin, and once the concept was approved we could really start to work on the aero design and everything,’ says Marquardt. ‘We were not far enough yet that we had to make things again, and we didn’t have a final concept, but we were already quite advanced and had some ideas and those we had to scrap.’The team was helped here by extensive use of rapid prototyping and 3D printing.

Work on the aerodynamics relied on a new algorithm that allowed a significant increase in CFD calculations, thus making it possible to use greater computing power to increase the number of possible simulations, before progressing to the wind tunnel. The same 3D measurement technology that was used on the BMW M4 DTM is also used on the BMW M8 GTE. The measurement system provides the perfect quality control once the racecar has been assembled. With such a complex car as the BMW M8 GTE, which is built completely by hand, it is essential that all the dimensions are correctly adhered to and implemented.

Delayed testing

The enforced delay meant that the car had to test later in the year than originally planned and in less than ideal conditions. However, much of the early testing was conducted with an adapted M6 GTLM, which allowed the team to evaluate key components for the M8 GTE.

‘If you ask the engineers, it was a disaster, too late, and they always need three more months,’ says Marquardt. ‘I have to say that if we would not have lost the four months a lot of things would have been easier. Better? I don’t know.’

‘We had to cut a few corners,’ Marquardt adds. ‘Whatever issue we had, we couldn’t examine the options of maybe A, or B, or C, as you normally would do, and find the best in terms of performance or efficiency. If we had an issue, we had to then decide what will solve the problem, and get it done, maybe not done in a fancy way, but just to solve that problem. We have managed very well to resolve the issues that came up and so far we haven’t encountered anything major that I can say is down to not having the time to sort things properly, so it is only things like the body fit on the car and small pieces like that.’

BMW has switched to Bosch electronics, leading to a very different cockpit layout, plus the rear view camera and collision avoidance system that was developed by Corvette and has since become widely adopted in GT cars. The system is able to recognise different classes of car, and their closing speed, aiding the driver in identifying where and when they will be passed. Audio warnings in the earpieces are also available in the Bosch system. ‘We also felt that we had more potential upwards with regards to functionality processing capabilities and so on with Bosch,’ says Marquardt.

Jens Marquardt says the four-month delay after the late ride height change decision meant BMW had to alter its approach with the M8
In the cabin the seat is fixed, with the pedals adjustable, while it has also been moved a little closer to the centre of the car

Safe seat

In terms of driver safety, BMW has, like Porsche, fixed the driver seat and the adjustability of this now comes from moving the pedals via a spring-loaded system, rather than an electronic system. The driver seat has moved closer to the centre of the cabin, although this movement was restricted by the transmission tunnel.

‘We have moved the driver seat as much inboard as you can in accordance with the regulations, but in our case, we have the transmission tunnel and that puts limits on what you can do,’ says Marquardt. ‘The tunnel is sacred and there is no modification allowed in this area at all. Even though there are other racecars without the tunnel now, I don’t know why [the GTE regulations are] so strict on those things, because moving the driver to the centre only helps safety and doesn’t have much impact on performance. People tell you about polar moment and all of that, but if you calculate the potential lap time gain for moving the driver 10cm inboard, it is not even visible. But, in terms of passive safety, we have done everything that we could.’


Work on the aerodynamics for the M8 GTE relied on a new algorithm that allowed a significant increase in CFD calculations

Hot laps

One of the major issues faced by the team is the car’s large greenhouse, the cockpit area that needs to be air-conditioned to a maximum temperature at the hot races. Porsche faced a similar problem and rectified it with a screen that effectively cut the cockpit in two and reduced the volume of air that needed to be cooled. BMW considered a similar solution, but then abandoned the idea. ‘You have to work a lot at blowing air onto the driver,’ says Marquardt. ‘To get such a big volume cool is one thing, but to get flow is the main thing. It’s completely different to a road car. We looked at splitting the cockpit, [but] we found more improvement with cooling the drivers. The cockpit temperature is one thing, but if a driver doesn’t feel cool, it doesn’t help things.’

BMW has decided to bring something completely different to GTE. For now, it has pulled the rabbit from the hat. Whether it walks the walk has yet to be seen.

TECH SPEC


Chassis/body: Composite body with carbon core and DMSB-approved safety roll cage; CFRP outer shell with quick-change concept.

Engine: V8 engine with BMW TwinPower Turbo Technology; 3981cc; 8-cylinder; 90-degree V angle; bore x stroke 899mm x 80mm; cylinder spacing 98mm; engine speed approx. 7000rpm.

Transmission: 6-speed sequential motorsport gearbox; electric paddleshift system; limited slip differential; CFRP driveshaft; Sachs carbon clutch.

Suspension: Double wishbones on front and rear axle; 4-way adjustable shock absorbers at front and rear; anti-roll bars with quick adjustment.

Electronics: BMW Motorsport in-house developed software functions for engine, gearbox and driver assistance; steering wheel with 16 buttons and seven dials; rear-view camera system with object recognition; high-performance headlights with OSRAM LED elements; live telemetry system for vehicle monitoring during races.

Wheels: BMW Aero rims: 12.5x18in on the front, 13x18in on the rear.

Tyres: Michelin, 30/68 R18 on the front, 31/71 R18 on the rear.

Dimensions: Length (without rear wing) 4980mm; width (without mirrors) 2046mm; width (with mirrors) 2224mm; height 1212mm; wheelbase 2880mm.

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