b20a? thats the engine from the old preludes. do you mean the b20b from the crv? anyways, they all have the same bore of 81mm except the b20b which has a bore of 84mm. the b16a has a stroke of 77mm. the b20b/b18a/b has a stroke of 89mm. and the b18c1/5 has a stroke of 87.20.

someone correct me if im wrong. h: