5w 30 is recommended but a lot of tuned cars on here (myself included) use 5w 40 because it stays a bit thicker when the engine is hot so when you're booting it it lubricates a bit better. Depends on your driving if you don't drive very aggressively or do lots of smaller journeys 5w 30 is best. Fully synthetic is more expensive but better. If you you want the best then most agree millers nanodrive CFS nt is the one to go for, its about £60 a bottle on Opie oils.