What is M20?
engine code for the small 2.5 liter or 2.7 liter (eta) 6 cylinder BMW engine that came in some of their cars during the 80s and early 90s such as the e30 3 series and e28 and e34 5 series.
The 1987 BMW 528e has a M20 2.7 liter eta engine.
See m42