Acura stated very early into their LMP2 program that LMP1 was their eventual goal, and therefore it's easy to consider the LMP2 project as simply a means to an ends.  And lessons learned over the first two years of the P2 program were clearly applied to the ARX-02a LMP1.  Seeing how effective a light weight LMP2 car could be up against heavier LMP1s on North American tracks didn't go unnoticed.  And even while stepping up the next rung into the heavier LMP1 class, the desire to continue to want to take advantages of those benefits began to plant the seeds for the ARX-02a.  

The ARX-02a was designed to compete directly with the diesel competition maximizing the advantages afforded to the package and minimizing the disadvantages.  And the use of the lightweight, normally aspirated, 4.0 liter LM-AR7 V8 was one of the pieces of the puzzle, more on that in a moment.  

But we must first consider that this engine certainly appeared to be a counter intuitive choice.  The engine was after all the, "...world's worst LMP engine," this according to someone very close to the program.  Consider that in order to match the diesels in power it would have to rev higher (relatively) at the sacrifice of reliability and fuel economy and there was little that could be done about the torque shortfall.   It appeared to be a bit like showing up with a knife to a gun fight.

But ultimately it simply wasn't feasible for Acura to develop a diesel engine to compete head to head with Audi and Peugeot as there simply wasn't an industrial base; Honda's expertise didn't include diesel.  While considered, an analysis of the regulations actually showed that a gas powered turbo V8 actually didn't give up much (if any) when looking at power, torque, and reliability, and came with packaging benefits.  And there also wasn't time to develop a hybrid gas-electric package.  This left Acura with few alternatives and it made sense to utilize what was already available to them, namely a "large" version (to the limitations of the liner thickness and the crank shaft) of the existing LM-V8 LMP2 engine.  

Bored out to 4.0 liters, the LM-AR7 carried over the IRL mounting points common to the LMP2 engine.  More importantly, the LM-AR7 allowed greater freedom in the placement of ballast compared to the competition's diesels.  Additionally, a normally aspirated engine certainly imparted an aero advantage over a diesel turbo; smaller radiators and no need for intercoolers.  

So going into LMP1, Acura was aware that they needed to maximize the advantages they had considering their package.  To that end, Wirth Research has designed the ARX-02a utilizing rear tires on all four corners.  The immediate benefit was a 7% gain in contact patch area.  But to make the fronts work effectively, a greater percentage of weight and downforce has to be applied to the front end of the car, more so than in a conventional car.  Which gets us back to elements such as the light weight engine; in order to maximize this concept the entire car was designed with this in mind.  And more interestingly, this wasn't a direction one would intuitively head given a conventional package.

A closed top design was considered during the development process, but upon further analysis there didn't seem to be any particular advantage.  And in fact, given the car's theme, the increased weight and higher CG that came with a closed top monocoque would have been cross purpose.

Nick Wirth indicated that approximately 15 days were spent scale tunnel testing at the Auto Research Center in Indianapolis.  But the bulk of the -02a's aero development was handled through CFD by Wirth Research's sister company, Digital Flow Solutions.

In retrospect it would seem the ARX-02a was a "budget" LMP.  There were many clues.  15 days in the wind tunnel for the -02a compared to nearly 80 for the ARX -01a LMP2.  That Honda didn't budget for the design of a bespoke LMP1 engine might also speaks volumes.  Couple that with the fact that only three monocoques were ever manufactured for the entire program (2 race + 1 spare) and the rumors of shortages and long lead times for spare parts from mid-season on.  Clearly something was going on behind the scenes regarding budgeting.

Years later we now understand that nearly on the car's debut, in January of 2009, Honda North America president Tetsuo Iwamura abruptly canceled the ARX-02a program.  With the cancellation of the project all development ceased (chassis and engine).  Most importantly, the -02a never benefited from bespoke compound and construction front tires that were predicted to have been worth 2.5 second at Sebring, had they been available (The ultimate irony is that with Peugeot and Audi's adaptation of the wide fronts concept just a few seasons later Michelin did end up manufacturing proper wide front compounds.).  The race program did see the year out though Highcroft were not keen on the early departure decision and attempted to negotiate running the car through 2010 (even though they already had a two year contract to do just that) and ended up returning the car weeks after the final race as a sign of their discontent.