I would like to explain few thinhs here for all those who are concerned with knocking and fuel quality. The problem is not with petrol, the difference comes in when different pumps add different quantity of ethanol in their tanks or the distributors do.the same. Ethanol is a substitute for petrol which is quite cheap and distributors mix it in petrol, as the ethanol has very low octane value so it decreases octane value of petrol as well and ultimately knocking occurs.
Now, normally people recommend hi-octane with normal petrol to avoid or minimize knocking and high octane acts an agent to bring back the octane level of petrol.
So it is advised to use few liters of hi octane with normal petrol if u r experiencing knocking or look for some very very well reputed pump who don't do.any such milavat of ethanol
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