93 vs 95 unleaded petrol – which one you should be filling up with

 ·17 Dec 2022

Many motorists wonder whether there’s a difference between 93 and 95 unleaded petrol and which is the better fuel to fill up with at the petrol station.

Some argue there’s no difference, while others say that 95 is better for fuel economy and performance – and the answer is both are somewhat correct.

Whether or not to use 93 or 95 depends wholly on the car you own, your driving preferences, and the environment in which you drive. In these days of high fuel prices, it would be a pity to waste money on the more expensive 95 unleaded petrol when your car only requires 93 unleaded petrol.

Speaking with News24, Sasol’s senior mechanical engineer Adrian Velaers said that many motorists believe that 95 petrol has more “energy” than 93 petrol, but that is not the case. “While 95 has a higher-octane value than 93, octane is not an indication of the energy content in the fuel, and this is where the myth comes in that 95 is better than 93,” he said.

Rather, the octane rating refers to the fuel’s resistance to “knocking”, which is a phenomenon of auto-ignition, where the fuel ignites in an uncontrolled manner. Thus the higher the rating, the greater the resistance, he added.

Performance

According to the AA, If you drive an average car that is naturally aspirated – supplied with air without the use of supercharging or turbocharging – then using 93-octane petrol is perfectly good to use, with no mentionable advantages to using 95-octane petrol.

If ultimate performance is not an issue for the driver, using 93 octane petrol is also acceptable even for a supercharged or turbo engine, said Velaers.

“For non-turbocharged engines, there is no benefit, 93 is essentially the same fuel, just cheaper. For turbocharged cars driven conservatively, there will also be no benefit to using 95 petrol instead of 93. If you care about maximum performance from your turbocharged car, then switching to 95 is a better option,” he said.

However, for car enthusiasts that enjoy the max performance and drive of their supercharged or turbocharged cars, its important to note that atmospheric pressure significantly impacts the in-cylinder pressures of naturally aspirated engines during wide-open-throttle (WOT), reported Carmag.

A study by Professor Andy Yates found that Johannesburg, for example, is roughly 1 700 metres above sea level, which means the atmospheric pressure is generally 17% lower than at the coast, explained Carmag.

This fact lowers the tendency of the engine to knock, allowing a lower-octane fuel to be used with no loss in performance compared with a higher-octane fuel in the highveld. On the coast, however, a drop in performance was realised as engines fitted with turbochargers boost the air pressure and make the engine more susceptible to knock – meaning they could use the extra octane at sea level, said Carmag.

This is why you won’t find 93 in coastal regions (e.g. Durban or Cape Town) because there is a risk of knocking, so you’ll have to use 95.

Fuel efficiency

According to Suzuki South Africa, an important consideration regarding fuel and engine efficiency when deciding on whether to use 93 or 95 petrol in areas like Johannesburg or Pretoria is to look at the size of the engine.

“If your car’s engine is a 1.6L or smaller, it’s unlikely that you’ll feel the difference between 93 and 95, while a 1.8L engine may experience a slight difference – getting more mileage out of 95.

“The true difference is noticeable in 2.0L, turbo and V6 engines and above, in these cars, manufacturers recommend only using 95 – or even higher at the coast,” said Suzuki.

Check your handbook

The CEO of the Retail Motor Industry Organisation (RMI), Jakkie Olivier, warns drivers considering switching octanes to check what the manufacturer specifications are for their vehicle, as you may be risking the warranty of the car.

“You need to bear in mind that it varies from manufacturer to manufacturer whether the warranty is affected by the owner’s fuel choice, so I recommend that you consult the owner’s manual before you finalise what fuel you’re going to use,” said Olivier.


Read: The cheapest new cars you can buy from every brand in South Africa – starting at R157,000

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