regular. only turbo models (wrx, sti, forester xt, etc.) need higher octanes.
You dont strictly need a turbo to warrant running premium petrol, I run my 99 impreza on premium and its a 1.5 non turbo. With premium, you see cleaner combustion and increased power (Bugger all mind you) and with regular you get.. well... regular haha. Premium will be more expensive but youll see a healthier and cleaner combustion per stroke
I was told by my Subaru tech that running premium in our N/A 2.5l engines can actually lead to greater carbon build up on our valve train. In short, he said it's not necessary at all, and it doesn't really improve your performance.
Looking for a Used Impreza in your area?
CarGurus has 11,067 nationwide Impreza listings starting at $1,899.
Search Subaru Impreza Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Subaru Impreza Experts