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The
R10's particulate filters have grown in diameter since the car's introduction
(note the bulge in the engine cover and compare to inset image below).
The placement of the exhaust is located to beneficially influence the trailing
edge flow of the rear diffuser by injecting high velocity airflow into
the air stream.
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The
rear diffuser gurney is fixed height (though replaceable/removable) where
as on the R8 it could be adjusted up or down as needed.
In
this shot you can see the mandatory plank that is bolted to the underside
of the car.
The
R10's high camber rear wing.
Louvers
accompany the rear fender.
At
the 2008 Spa Le Mans Series event the Audis were running in a slightly
revised aerodynamic spec which consisted of a simple add-on "wing" mounted
between the rear fenders at the very trailing edge of the engine cover. 
Having
a closer look at the wing and it appears to be a simple parallel extrusion
in cross section without a differing top and bottom chord line (ie, not
a true wing but we'll use that wording from here out for clarity sake,
I mean what else are we going to call it?). Overall it seems rather
crude in execution and is very simplistic.
Perhaps
the most telling feature of this device's function are the related cutouts
in the trailing edge of the rear bodywork which allows the low pressure
zone that is generated by this wing to potentially "see" the trailing edge
of the tunnels. And given the proximity, there's potential for some
(minor) positive interaction with the underfloor.
In general, the new wing would appear to allow a reduction in angle of the primary rear wing flap for less drag but similar levels of downforce, and quotes by Audi's Ralf Jüttner backs this up.
Interestingly enough, a cursory read of the regulations and one really questions the legality of such an aero device is based solely on the wording in article 3.6.2 which states in rather plain language:
3.6.2 - No aerodynamic element can be added on the bodywork apart from :
- Two aerodynamic elements maximum at the front of the front fenders provided that :
• They do not obstruct the driver's view
• They do not mask the headlights ;
• They are not situated more than 600 mm above the reference surface ;
• They are approved by the manufacturer and the ACO (homologation form of the car).
- One “Gurney” at the rear of the
bodywork.
- The rear wing described below.
So it seems rather clear that said add-on device isn't, a.) an element attached to the front fender, b.) a rear body gurney (the cars still had the standard trailing edge gurney being run in conjunction with the new device), or c.) a rear wing. So naturally there are questions as to how Audi defined this aero device and then to what standard the ACO accepted it.
