Hi.
I know the recommended fuel for 525efi is 87 octane, but here in Norway the lowest we have is 95 octane E10 and only 98 octane without ethanol. I belive 95 here is 91 US and 98 is 93 US
Is it necessary to tune the engine for the higher octane? Just to make it burn better and maybe reduce the gasoline smell from the exhaust ..

Run 98.

Not necessary to tune, but higher compression heads would give more power.

Ok, thanks

It is perfectly fine to run your 95 RON in the 525EFI and no need to do anything

Clarification: the reason to run 98 is that it is ethanol free.

Its not necessary, but you could see if has Whipple has an upgraded tune for the higher octane.

Yes my plan was to send them the ecu for the wipple tune. I think I read somewhere that running higher octane then 87 on this engine could actually hurt performance. Is this true?

Theoretically, yes.

Practically, no.