Everything from B16A to B20A5 is 81 mm bore with strokes ranging from 77 to 95 mm.

The B21A1 ('90-'91 USDM Prelude Si) was basically a B20A5 (95 mm stroke) with an 83 mm bore.

The B20B and B20Z are variations on the B18B (89 mm stroke) but with an 84 mm bore.

The B18C has an 87.2 mm stroke, the B17 is 81.4, and the B16 is 77.