Honda B20A engine

The Honda B20A engine series, known as the B20A and B21A was an inline four-cylinder engine family from Honda introduced in 1985 in the second-generation Honda Prelude. Also available in the contemporary third-generation Honda Accord in the Japanese domestic market, along with the Accord-derived Vigor, the B20A was Honda's first line of multivalve DOHC inline four-cylinder engines, focused towards performance and displacing 2.0 to 2.1 litres.

The third-generation Prelude was exclusively powered by the B20A engine family and production of the B20A engine family ended with the conclusion of the production of the third-generation Prelude in 1991.

It would be succeeded by the Honda B engine. Although sharing similar nomenclature and some design elements, the earlier B20A substantially differs from the later B-series in architecture enough to be considered two different engine families and must not be confused with other B-series engines and the B20B, a 2.0 liter DOHC engine introduced alongside the Honda CR-V in 1994.