It says either 15W/50 or 20W - 50 for the engine and carb dashpots in my Rover SD1 workshop manual. The main gearbox transfer box (provided they are series selectable 4wd type), axles and steering box take EP90. Nice engine that - They are more powerfull than the Range Rover and Land Rover carb V8s because they have a higher compression ratio, bigger valves and more efficient SU carbs. If it doesn't already have them then Range Rover 3.9 V9 exhaust manifolds and down pipes will get a bit more power out of it.