For a brief period in the early 1990s, sports prototype racers were closely related to contemporary Formula 1 cars. This was the result of identical engine regulations, devised to make F1 a more appealing prospect for the many manufacturers that were active in sports car racing. It led to some of the finest racing cars ever built but eventually the FIA got their way and almost every big manufacturer jumped onto the F1 bandwagon. Of course there have been similarities in designs since but no sports car has come so close to F1 than the new Acura ARX-02a launched early in 2009. This is no coincidence as the chassis and bodywork were designed by Nick Wirth's company. Most of his past experience lies in Formula 1 both as a designer and team owner.
Developed by Wirth Research in England and Honda Performance Development in California, the Acura LMP1 racer has taken the 'F1' route more by necessity than by choice. With the ARX-01a/b LMP2 racer used with considerable success in 2007 and 2008, Acura ran a similar engine as its biggest competitors, a Naturally Aspirated 3.4 litre V8. The engines used in LMP1 are more diverse and despite the ACO's best efforts, performance is certainly not equal. The method used by the French governing body is to restrict air-flow to the engine according to its size and aspiration. Although this a good way to limit power high in the rev band, it does little to cut torque and that's why diesel engines still have an advantage. With almost all of Acura's production cars powered by Naturally Aspirated petrol engines and only a limited budget available, the team had little choice but to further develop the existing V8 engine. The chassis would have to make up for the deficit.
With power at a premium, Nick Wirth concentrated on generation as much mechanical grip and downforce as possible. Things were complicated further with changes in the regulations considering the maximum width of the rear wing. Wirth's unusual solution was to fit rear tires on the front, increasing the contact patch by 7%. One of the drawbacks was the need for wider front fenders, which came at the expense of the space between the fenders and monocoque. This limited the all important airflow passed the monocoque into the side-pods. To solve this, Wirth developed a raised nose with a 'zero keel', almost identical to that of a current F1 car. The big difference is the width of the monocoque required for the sports car's 2-seater layout. The combination of the wider wheels and 'zero keel' nose leaves little room for the suspension arms. These were of conventional design except for the relatively long torsion bars. Both front and rear suspension feature push-rod actuated dampers and a 'third' damper to provide additional balance.
While the chassis was developed in England, HPD reworked the 3.4 litre V8 engine. The displacement was raised to four litre by reworking the crankshaft. Interestingly the heads were carried over. With the current restrictors the high revving V8 produces in excess of 620 bhp. One of the main advantages of the Naturally Aspirated V8 is its size and weight. It also requires far fewer ancillaries than the heavy and complex diesel engines. The new LM-AR7 engine is bolted to the monocoque as far forward as possible to get the best weight balance. The six-speed gearbox was sourced at British expert Xtrac. It is operated by paddles fitted behind a bespoke steering wheel. Similar to a F1 steering wheel, it incorporates the dashboard display. The running chassis of the ARX-02a is a showcase of minimalistic design. It weighs in well under the 900 kg minimum, which offers the opportunity to carefully adjust the balance with the ballast.
With its sharp and elegant lines, it is hard to imagine that the Acura was designed to generate maximum downforce. That's exactly what is needed on the tight and twisty tracks used for the American Le Mans Series (ALMS). For the development of the aero-package Wirth used Computational Fluid Dynamics (CFD) and more traditional wind-tunnel tests for the really complicated simulations. If Acura decides to race the ARX-02a at Le Mans, a complete redesign of the body would be required. To make the most of the smaller rear-wing, Wirth's team developed a new mounting method. The so called 'swan necks' allow for a maximum amount of surface area of the wing. Interestingly Audi came up with exactly the same solution without ever seeing the Acura's new rear wing. Even the unusually thick front 'dive-planes' are designed to send more air over the rear wings.
Two cars were assembled, one for de Ferran Competition and the other for Duncan Dayton's Highcroft Racing. Ahead of a full ALMS seasons, the ARX-02a was first seen testing at Sebring late in 2008. By that time it had become clear that there would be no serious competition in the LMP1 class during most of the races. However at the season opener, the Sebring 12 Hours, the two Works supported Acura teams would face the might of the Audi and Peugeot teams. With the confirmation of the four diesel cars, there was plenty of incentive to push on and have the new Acura ready. The public debut came at the official 'wheels down winter' test at Sebring during the end of January. Instead of trying to shield the car from their prying lenses, photographers were all invited to a closer look at all the details. With no other LMP1 cars present, it was no surprise that the two ARX-02as were quickest.
The first real test came at the Sebring race-week halfway through March. Peugeot brought their seasoned 908 HDI Fap Coupe and Audi debuted the R15 TDI. The new Audi boasted a diametrically opposed design philosophy. Unlike the ultra-clean Acura, the R15 has many intricate aerodynamic elements to make the most of the airflow. It was quite amazing that the same regulations could form the basis for three so very different designs. Even more amazingly the three machines managed to set quite similar lap times. In the pre-race test and practice sessions the diesels were regularly a little quicker but not much. During qualifying on a completely clear track, Scot Dixon in the de Ferran car set an amazingly quick lap time that proved to be good enough for pole. Acura's weekend was already a success and Wirth had proven that a really good petrol car could be as quick around a lap as the diesels.
During the first hundred meters of the race a slightly different picture emerged. The immense torque of the diesel allowed the second placed Allan McNish to immediately pull clear of Dixon on the start/finish straight. After only a few laps the four diesels had grabbed the lead, leaving the new Acuras back in fifth and sixth. Relying so much on maintaining their momentum in the corners, the Acuras lost a lot of time in traffic. Eventually both cars retired from the race with technical problems. In race conditions the torque of the diesels made the difference and sadly there is little mechanical grip or downforce can do about that. After Sebring Audi and Peugeot returned to Europe to concentrate on their Le Mans preparations. It is uncertain whether either will return to the United States later in the year and until then the two Acuras will race each other.
Three weeks later at the short St. Petersburg ALMS race the two Acuras were back out. De Ferran's car clinched pole but once again suffered from a break down. This left the honour of clinching the ARX-02a's first victory to the Patron Highcroft car driven by Scott Sharp and David Brabham. Development work is currently focused on reliability but there is more to come from the engine would the Acura's be challenged again. Whether that would ever be enough to counter the might of the diesels is highly debatable. Even before Sebring there were rumours of the plug being pulled but hopefully Wirth Research and HPD are allowed to continue but in these difficult times nothing is certain. From 2011 onwards new regulations will come into effect that will suit the lean and mean ARX-02a even more than the current ones. Until then the Acura will certainly win many more races.
Article by Wouter Melissen, last updated on April 13, 2009
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