The next petrol model up was the six-cylinder 520i, which began production in January 1988. It was initially powered by the BMW M20 single overhead camshaft engine, which was replaced by the BMW M50 double overhead camshaft engine in 1990. The 520i was the second most popular E34 model globally, with 426,971 units produced. The 525i was the most popular E34 model globally with 434,549 units produced. As per the 520i, the 525i initially used the M20 engine, which was replaced by the M50 engine in 1990.