All the info you want here : http://foc-u.co.uk/index.php?action=downloads;cat=4
As a guide Fully synthetic 10W-40 for racing and track days and Semi synthetic 10W-40 for everthing else.
I use 10W-40 Semi senthetic all the time Silkolene or Castrol Motorcycle specific oil (I can get it at the right price), but have used non friction enhanced car version 10W-40 semi synthetic for years without any problems.
Which you go for is a personal decision,
If he was using Halfords semi synthetic, was it the car verson or motorcycle version?
As a guide Fully synthetic 10W-40 for racing and track days and Semi synthetic 10W-40 for everthing else.
I use 10W-40 Semi senthetic all the time Silkolene or Castrol Motorcycle specific oil (I can get it at the right price), but have used non friction enhanced car version 10W-40 semi synthetic for years without any problems.
Which you go for is a personal decision,
If he was using Halfords semi synthetic, was it the car verson or motorcycle version?