| 
Help
A common myth is that using premium or super-grade gasoline (like Speed, XtraPremium or Power) will give you more power and better mileage, and make your vehicle’s engine run smoother as bigger octane numbers are always better.
Reality Check! With the exception of a small percentage of automobiles (mainly sports cars) that require high-octane petrol, using plus or premium-grade petrol won’t do anything for your car beside decreasing the efficiency.
Know Why High Octane Fuel Is Not Always Good For Your Car…?
The reason why this myth exists: Octane number is a measure of anti-knocking properties of fuel (Petrol). The higher the octane number, better the anti-knocking properties (knocking is the phenomena in which the fuel pre-ignites and starts to burn before its ignition time i.e. the time when spark plug creates a spark, hence creating unnecessary sound and shock waves which damage the engine and decrease the power output). So people think that it will be better to go for higher octane numbered fuel.
Things That Also Matter: Octane number also shows how much compression (when the piston is squeezing the fuel and air inside engine cylinder) the fuel can withstand before ignition. As the octane number increases the compression ratio it can withstand before ignition increases too. This means that a higher octane fuel like 97 compared to 91 takes a higher amount of energy (which is generated by increasing the compression ratio) to initiate the combustion reaction within your vehicle’s cylinders. So to burn higher octane numbered fuel you will need an engine with high compression ratio.
However, a vehicle designed to run on 91-octane, as most vehicles are today, will not benefit from a higher octane fuel. It will just waste money. And if your vehicle is designed to run on high octane or premium fuel, including many sports cars, you can lose fuel efficiency by switching to a lower rated fuel. Normal cars don’t have high compression ratio to burn the premium fuel (Speed, XtraPremium or Power) easily and efficiently. But sports cars’ engines have that, so a premium grade fuel is better for them.
Now Here Is What You Need To Do…
Only a very small percentage of (mostly premium) automobiles benefit from high-octane fuel. For instance, the high-compression engines in sports cars. Most of the regular cars you see on the roads have lower compression engines. The rule of thumb here is to use nothing lower than what your vehicle’s owner manual tells you to. If your car is designed to run on 91-octane, use 91-octane because using 97 won’t really make any difference at all.
Last but not the least, octane ratings are not indicators of the energy content of fuels.
