CREATE TABLE table_5841 ("Race" TEXT, "Length" TEXT, "Class" TEXT, "Circuit" TEXT, "Date" TEXT)

What was the length for GT class at Portland International Raceway?
SELECT "Length" FROM table_5841 WHERE "Class" = 'gt' AND "Circuit" = 'portland international raceway'
SELECT "Length" FROM "table_5841" WHERE "Circuit" = 'portland international raceway' AND "Class" = 'gt'