Complex sentence: The last series to hold on to this set of rules was the BTCC, in 2000, but the current World Touring Car Championship regulations are very inspired in the old series, with production-based four door sedans powered by 2.0 L engines.
Split into simpler sentences: The last series to hold on to this set of rules was the BTCC in 2000. The current World Touring Car Championship regulations are very inspired in the old series, with production-based four door sedans powered by 2.0 L engines.