The
ARX-01a's most characteristic detail feature is the variable height
front splitter. We presume that the variable height allows more
consistent front underfloor air flow and thus front downforce
for given dynamic ride height changes. 
The raised sections in the splitter blend reward to form tunnels/channels in the diffuser section.
The
trailing edge of the front diffuser tunnels. Note the large
height difference between the diffuser trailing edge and the bodywork
above it, the significance being the lack of a resolved common trailing
edge. Contrast this to the ARX-02a LMP1 car's front diffuser trailing edge.
The
trailing edge detail on the Acura's front diffuser strakes consist of a series of serrations. These
serrations promote the generation of vorticies.Close up of ARX-01a strake serration  |
In 2009 the front diffuser strake's leading edge was trimmed short.
The ARX-01a
manages the air flow exiting the front diffuser by directing it out the
side of the car aft of the front wheel. Note the small vent just
aft of the front wheel to manage from wheel well airflow. The
side pod tucks in and is scuplted on its lower half to help with
the flow extraction.
Looking
at a close up of the -01a's turning vane we can better see the
sculpting on the side pod as well as the delicate appearance of the
turning vanes themselves.
The
most dramatic change on the ARX-01b differentiating it from the ARX-01a
were the revisions made to airflow management just behind the front
wheels. The side pod was lowered and
disconnected from the front fender.
This opened up the front diffuser exit and improved efficiency as
well as increasing front balance and overall downforce (when
rebalanced). Notice the simplified turning vane which now has
only two legs instead of three. 
In 2008 a very short extension was added to the trailing edge of the front fender. In 2007 the Audi R10 had a similar detail. 
From
this shot of the Strakka Acura ARX-01c, here at Le Mans 2010, we can
see a few more of the multitude of changes of the -01c over the -01b:(1)The turning vane is now attached to the side pod
(2)The bottom edge of the pontoon fender is offset inboard
(3)The mirrors have been relocated
(4)The general detailing is different in this area
The louvers are the low drag variety.
It was our understanding that Porsche
was behind a (albeit small) protest of the Acura chassis at Sebring 2008. In response, IMSA made Acura add a inboard fender extension in order to make the cars compliant with
Art 3.4.1 a/ that states:
[bodywork] As viewed from the side, must cover the whole circumference of the complete wheels (wheels and tyres) above the axle centrelines level with no empty space or cut-out in the bodywork.
The inboard fender extension can be seen as the small (approximately 2.5" x 1.75") carbon add-on (riveted) just ahead of and below the horizontal valence panel. Ultimately one wonders how anyone at Porsche had such a close look at the car to make a determination that the car was in violation, though Porsche's Michael Pfadenhauer was clearly oogling the Highcroft Acura as it sat stuck in a paddock traffic jam, presumably making sure the cars were finally in compliance. Nick Wirth would only offer this, "I hope they are worried."
