thanks for the replies mates.. Ya i went through that specific thread too..
From what i read long time back and this new one i found the Octane rating for Vios is 93
http://english.sinopec.com/products_service/oil_products/
I did use 90 OCt once when i was out of colombo n i felt the car was not giving the usual performance.. So a bit worried to use 90 OCT..
I'm a newbie to this so i fear it wud make my engine go bad.