Join Date: Dec 2016
Location: Northumberland, England
Car Year: 2003
Car Model: Forester AW
Transmission: Manual with low ratio
Feedback Score: 0 reviews
Hi Ian, in simple terms, U.K. Unleaded is 95 RON, but SUPER unleaded ( under different brand names ) is 97 to 99 RON. It costs a few pence per litre more than standard unleaded, hence the original title of the post.
It's really super unleaded you should use, to get the designed horsepower out of your engine.
Most folks seem to prefer Shell V power, but some of those folks with a Tesco station nearby ( not everyone does!) seem to use Tesco super unleaded with little or no difference noticed. I guess any available ( to you) super unleaded will be better than standard unleaded 95 though.
Don't forget, it might take a good few miles or a tankful or two for the ECU to fully optimise and fine- tune itself to the move from 95 to 97-99. There used to be good You tube clips ( sorry don't have the links handy) showing Impreza Sti,s in particular, giving 270-290 or more hp on v power, and dropped by to 220 or so, just switching to plain unleaded 95 RON.
Personally, with non- turbo (N/A, or normally aspirated) engines in our Subaru,s and a Shell station nearby, I use Vpower, not that it probably gives any extra hp in these motors, but I do get at least 10% extra mpg and it runs much more responsively, especially noticeably at low to mid revs and stronger just above tick over speed. So it pays for itself in better mpg.
2003 Forester AW, 2005 Impreza GX