Hi again,
Not sure when the revised engine was introduced. I think it may have been mid-1999. My engine is designated "B5244 S2" if that helps. The S2 may indicate series 2. If you ring a volvo dealer or volvo uk they may know when the change took place.
Details of the new engine can be found at
www.autoworld.com/news/Volvo/RevisedEngines.htm
under the heading: "Volvo's new revised engines - greater driving pleasure, quieter operation and lower fuel consumption."
I can attest to the above. At 80mph on French motorways (where tyre noise is less intrusive - better surface)you just here a faint background swoosh of air around the car.
Ray