What’s the difference between regular and high-octane petrol?

Can you please explain the different grades of petrol available in the market and how 95- and 100-octane petrol affects the performance and efficiency of different types of petrol engines? I remember reading that direct-injection turbo engines would benefit from higher-octane fuels. However, I guess most mass-market manufacturers tune their engines to run on the lowest available octane. So, is there any benefit of filling 95-octane petrol without reprogramming the car’s ECU?

Fagun Suchde, via email

Autocar India says: The octane number (RON) of gasoline represents the fuel’s ability to resist knocking. A higher octane is more resistant to uncontrolled combustion or detonation, which is a key characteristic demanded by high-compression engines.

Most mass-market cars, typically using naturally aspirated engines, are calibrated to work reliably on the default petrol available in India – 91 octane. However, gasoline direct injection (GDI) engines, such as the VW Group’s 1.0 TSI, 1.5 TSI and 2.0 TSI, Hyundai’s 1.0-litre GDI, Tata Motors’ 1.2 GDI, and several luxury cars tend to benefit from a minimum of 95 RON fuel.

The higher octane number offers better combustibility in these high-compression engines, which also get the requisite ECU programming. When subjected to gasoline upwards of 95 RON, these engines adapt the ignition timing to offer 3-5 percent better power and fuel efficiency compared to when functioning on 91 RON fuel.

Indian Oil’s XP95 and XP100, Bharat Petroleum’s Speed 97, and Hindustan Petrol’s Power99 are some of the high-octane gasoline fuels available in India to cater to modern GDI engines, as well as the powerful engines present in high-end luxury and sports cars. 

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