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 second line of multivalve DOHC inline four-cylinder engines behind the "ZC" twin-cam variant of the ordinarily SOHC D-series, 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.
History
The B20A would be succeeded by the Honda B engine family. 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 is also not to be confused with the B20B, a 2.0 liter DOHC engine introduced alongside the Honda CR-V in 1994.
There were two versions of the B20A:
The first generation of B20A engines was available in the 85–87 Prelude 2.0SI in Japan and in Europe, the 86–89 Honda Vigor and Accord. It leaned towards the front of the car just like the A20A engine found in the same cars. This B20A produces 160PS (118kW) and 140lb⋅ft (190N⋅m) torque in Japan. In Europe this is called B20A1, producing 137hp (102kW) and 127lb.ft (172 Nm).
The second generation of B20A was found in the 87–91 Prelude. The 87–91 Prelude B20A and B21A blocks are cast so they lie at an 18-degree angle leaning towards the firewall. This was done to please the exterior specifications for the 1988–1991 3rd Generation Prelude due to its ultra-low hood line which Honda dubs the "engineless design" and also for handling reasons; placing the engine at an angle gives it a lower center of gravity (similar to straight 6 designs in older BMW's).
There was also a similar engine named B18A for the 86–89 Accords and Vigors. It was a de-stroked B20A powered by two side-draft Keihin carburetors.
All B20A engines consisted of closed-deck aluminium blocks with thicker-than-average iron sleeves whereas the B21A1 had FRM (fiber reinforced metal) cylinder liners.
The B21A1 was basically a re-worked B20A5 with an increase in bore to 83mm (3.3in). The external block dimensions had to stay identical (although there was increased external strengthening and webbing on the B21) to the B20A5 block so Honda called upon Saffil to create a thin but strong cylinder liner using FRM (fiber reinforced metal) which consisted of a carbon fiber matrix, aluminium alloy, and aluminium oxide to make a very strong cylinder sleeve. The sleeve is so strong, in fact, that it wears out the piston rings, causing low compression numbers, severe smoking, and high oil usage. It is possible in many situations to merely replace the worn rings in order to revive the motor's former output. Many machine shops will not attempt to re-hone or re-bore the FRM sleeves, as this type of sleeve will de-laminate during machining operations.
B18A
The original B18A is a short-stroked version of the B20A. It is not considered to be part of the modern B-series family, despite sharing its dimensions with the later B18A1.
(JDM GOLD TOP B20A 1985.06–1987.04) 160PS (118kW) at 6300 rpm & 137lb.ft (186 N·m) at 5000 rpm (!JIS Gross data), using PH3 ECU
(JDM BLACKTOP B20A 1987.05–1989.08) 145PS (107kW) at 6200 rpm & 127lb.ft (173 N·m) at 4000 rpm (!JIS Net data with new dual-stage intake manifold), using PH3 ECU
(EDM, B20A1 Gold Top) 137PS (101kW) at 6000 rpm & 127lb.ft (172 N·m) at 4000 rpm, using PJ5 (602,603,752), PJ7, PH3 ECU w vac. advance
Transmission: B2K5(86–87), F2K5(88–89)
The B20A installed in 1988–1991 Preludes have the following specifications:
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