 In 1940 an improved fuel, designated "C2" was introduced having a higher aromatic content of 35–38% and giving performance equivalent to Allied 100 octane grade of that time.C2 was used in small quantities by aircraft such as the Messerschmitt Bf 109E-4/N and E-7/N and the Messerschmitt Bf 110C when equipped with the DB 601N engine, that entered series production in October 1939.The power was increased by 20% over that of the DB 601A, to 1,260 hp at 6,900 feet (2,100 m) at 1.35 atm boost pressure and 2,400 rpm.