
Originally Posted by
jut703
There aren't any hard and fast rules when it comes to fuel consumption and octane rating.
For most cars, there's no difference whether you fill up with 91 RON or 95/97/100 RON fuel. If a car is designed to run with 91 RON, it will not develop more power or give better mileage by using higher octane fuels.
Even high-compression engines like Mazda's SkyActiv, when tuned to run on 91 RON, will run perfectly fine on 91 RON and will not get better efficiency from 95 RON.
Remember that a fuel's octane rating only signifies its resistance to knocking (premature ignition). It means that the fuel can withstand more compression before igniting, it does not mean that the fuel has more energy or is more efficient.
On cars that are designed for higher octanes, such as most sports cars, you will suffer a reduction in performance/economy when using fuels with lower octanes than what's specified in the manual. This is because the car's anti-knock sensor detects that the fuel ignites prematurely, and will adjust the ignition timing to prevent engine knocking. It results in sub-optimal conditions for the engine, resulting in decreased power, but this is better than continuous knocking which can lead to engine damage.
If you would notice, no oil company claims that their 95 RON fuel will generate more power or better economy than their 91 RON just because of the higher octane. Rather, all their claims are based on the fact that their premium fuels have better cleaning properties for your engine because of the higher detergency of the additives used in premium fuel compared to regular fuel. Additional power or improved economy are only potential offshoots of a cleaner engine.
However, no company discloses just how much cleaner your engine will be with V-Power/XCS/Excellium compared to FuelSave/Xtra Advance/Techron Silver. This is because the difference is mostly negligible and your engine's longevity won't suffer just because you use exclusively 91 RON.
Oil companies invest heavily on marketing their premium fuels simply because you pay several pesos more for it, even if the difference in product cost is just a few centavos.
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