Due to poor quality of super in our country every car knocks even new Mehran efi. So now a days best practice is to refill your petrol tank fully with hi-octane or maintain a certain ratio b/w hi-octane & super. Other than that my personal experience says, cultus starts knocking if you don't use combination of hi-octane & super .at every refill at least use 30% of hi-octane and 70% super otherwise it will knock when u will touch accelerator pedal to the ground on 3[SUP]rd[/SUP], 4[SUP]th[/SUP] and 5[SUP]th[/SUP] gear.