Saw an R8 today...

[Ti Kan]

The Mazda 4-rotor IMSA GTP car that was LOUD was the RX-792P circa 1992.
The noise it made matched Larry's description perfectly.  I guess it's
got similar engine bits as the Mazda 787 GTO car and therefore
the same cacophony:

http://www.mulsannescorner.com/RX-792P.htm

Mandatory Audi content: The 2006 24 Hours of Le Mans is this coming
weekend June 17 and 18, where the Audi R10 TDI will attempt to make
history as the first diesel powered cars to win this event.
Don't miss it!

http://www.lemans.org/24heuresdumans/live/pages/accueil_gb.html

-Ti