CREATE TABLE table_33406 ("Year" FLOAT, "Chassis" CLOB, "Engine" CLOB, "Start" CLOB, "Finish" CLOB, "Team" CLOB)

What chassis was used with the Chevrolet engine in 1991?
SELECT "Chassis" FROM table_33406 WHERE "Engine" = 'chevrolet' AND "Year" = '1991'
SELECT "Chassis" FROM "table_33406" WHERE "Engine" = 'chevrolet' AND "Year" = '1991'