Quote:For the upcoming 1974 B210 introduction in USA -- with its heavy features (400 lbs heavier than B110 and 120Y) -- Nissan needed more grunt than the A12. So they created the A13, a stroked engine with longer crank throws than the A12. It was the first tall block, and immediately was upgraded to A14 for 1975

Now come 1977 and again more than A12 was needed, this time for the Japan market base B310. So a new A13 was created with +2mm bore size but still using the standard A12 stroke. I haven't seen an official reason for the change, so maybe it was one of the usual:
* To keep pace with competition (e.g. Corolla specs: E55 already had 1.3 engine and base E70 would start at 1.3)
OR
* Power/emissions changes (e.g. to meet the Showa 53 (1978) "H" level emissions)