CREATE TABLE table_25214 ("Year" TEXT, "Date" TEXT, "Driver" TEXT, "Team" TEXT, "Manufacturer" TEXT, "Laps" TEXT, "Miles  ( km ) " TEXT, "Race Time" TEXT, "Average Speed  ( mph ) " TEXT, "Report" TEXT)

When was an average speed of 81.388 mph recorded?
SELECT "Date" FROM table_25214 WHERE "Average Speed (mph)" = '81.388'
SELECT "Date" FROM "table_25214" WHERE "Average Speed (mph)" = '81.388'