I was looking through all my Air Race books and the only mention of an asymmetric wing in the post war (1946-present) racing era was the much modified P-51 named "Beguine". This was the plane which moved the radiators to pods in the wings. The owner chopped the left wing down "shorter than the right" (doesn't mention how much). The plane crashed in 1949 which effectively ended the Cleveland Air Races (Well, that and the Korean War).

Nobody knows the cause of the crash but witnesses say he rolled rapidly to the left and then slow rolled to the right before crashing into a house. Pilot witnesses say he may have misjudged his turn into the pylon and tried to roll out but couldn't retain control.

Speculation of the crash on my part - Low time pilot and an assymetric cut on the wing.

Good books to get:
RacePlane Tech #1: Griffon Powered Mustangs
and
Raceplane Tech #2: Round Engine Racers - Bearcats and Corsairs

Cheers!
Reno Bound 2003
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Don