Database: cars
Question: What is the percentage of cars that was produced by Japan among those that have a sweep volume of no less than 30?
SQL: SELECT CAST(SUM(CASE WHEN T3.country = 'Japan' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM data AS T1 INNER JOIN production AS T2 ON T1.ID = T2.ID INNER JOIN country AS T3 ON T3.origin = T2.country WHERE T1.displacement / T1.cylinders > 30