Spark plugs: B 6284 T: P/N 271367-4 (or equivalent)
B 6294 S: P/N 272371-8 (or equivalent)
B 5244 S: P/N 272313-8
Spark plug gap: 0.028-0.032" (0.7-0.8 mm)
Tightening torque: 18.4 ft. lbs. (25 Nm)
The above is from your owners manual, page 122...also found in electronic form here: https://www.customers.volvocars.com/own ... s80_00.htm
Personally, I would gap them down under 0.030 inches... as well as use genuine Volvo plugs or cheaper Bosch copper cores and stay away from fancy or expensive Platinum plugs (others have had many issues with these). Good luck and hope this helped you.