It has been a challenging start to the year for Malaysians, with fuel prices going up in both January and February. As of now, a litre of RON 95 will cost you RM2.30, while it’s RM2.60 for RON97. Analysts are predicting that this gloomy trend will continue into the year, with further hikes expected to be announced in the coming months.
As with every increase in fuel prices, Malaysians will no doubt come up with creative methods or “wise tips” to ensure they minimise their fuel consumption. A more recent, and popular tip being passed around states that using the more expensive RON 97 petrol will provide better savings, as it is claimed to provide more efficient combustion.
However, is there any truth to such claims? Well, our colleagues (Farid and Durrani) from paultan.org/bm decided to perform a real world test together with other media members from the automotive segment of Buletin Utama, to see if there’s any truth to this theory.
Similar to our previous test (RON 95 vs RON 97), the team used two identical cars – a pair of Proton Saga sedans – to ensure it remains relevant to most Malaysian car owners who may not have the means of owning a more expensive car, and is likely more affected by fuel price hikes. Both Saga cars used here are the Premium CVT variant, powered by a 1.3 litre naturally-aspirated four-cylinder petrol engine mated to a CVT.
The day before the test, both cars had their fuel tanks completely drained before being filled with petrol to ensure the cars’ ECU is adjusted automatically to the type of petrol (RON 95 or RON 97) that will be filled tomorrow. The grey car received RON 97, while the black one would represent RON 95.
To ensure maximum parity, the tyre pressure on both cars were adjusted to meet Proton’s specified amount of 220 kPA or 32 psi. Additionally, all cargo spaces in the cars were emptied out to ensure no excess weight tampered with the findings, and the air-conditioning settings were set to be identical as well.
On the day of the test, the team assembled at the Petronas station in Taman Tun Dr Ismail (TTDI), and filled both cars using the ‘three click’ method (wait until the pump nozzle stops automatically, repeat for three times).
After filling up the cars, the team departed at about 10am towards Kuala Lumpur to simulate the usual jam associated with driving in the city centre. The drive within the city covered a distance of about 30 km, where Farid and Durrani swapped cars at the 15 km mark to counteract the difference in driving styles. The position of both cars, whether it is the lead or follower, was also changed so any gains from ‘drafting’ is negated.
After the tour of KL, the team made their way to Hulu Yam via Gombak, followed by Batang Kali and Tanjung Malim, opting not to use the main highway and instead, use the old trunk roads. As before, driver changes took place (after 50 km) and the position of the lead car changed every 20 km.
From Tanjung Malim, the team then made the journey back to Petronas TTDI via the North-South Expressway (NSE), adopting the same driver and lead car swaps as mentioned. By the end of journey, the RON 95 Saga (black car) covered a distance of 171.4 km, while the RON 97 Saga (grey car) notched up 171.8 km, with an average distance 171.6 km between both cars.
Both cars were then refuelled using the same ‘three click’ method from the same pumps as in the morning, before any math can commence. The result, the RON 95 Saga used 11.701 litres, while the RON 97 Saga used 12.240 litres.
Crunching the numbers, the Saga that ran on RON 95 consumed 6.8 litres of fuel per 100 km (or 14.65 km/l), with the total refuelling cost amounting to RM26.91 or 15 sen per km.
Meanwhile, the RON 97 Saga recorded a fuel consumption of 7.1 litres per 100 km (or 14.04 km/l), costing RM31.82 in total or 18 sen per km. The conclusion from this test is using RON 95 is 3 sen per km cheaper compared to RON 97.
What about the other aspects? In terms of performance, the team did not notice any substantial differences while driving both Saga cars, including in terms of acceleration. This is pretty consistent with the English team’s test involving Volkswagen cars previously, which ended in similar fashion – cars with RON 97 used a little bit more fuel compared to RON 95-filled cars.
So, what is the technical explanation behind the results of this test? While most would believe that the fuel with the higher RON number is “cleaner,” and will burn more efficiently to produce a bigger bang, this isn’t the case.
RON or Research Octane Number is associated with the fuel’s resistance to detonating while under high compression, without any form of ignition (spark plug). The higher the RON number, the more compression the fuel can withstand before detonating.
Should the fuel detonate before it is fully compressed and ignited, this will cause pre-ignition followed by engine knocking. The disadvantages of this are engine damage, wastage of fuel, sub-optimum power output and higher maintenance costs.
Among the factors that can cause engine knocking are carbon deposits that accumulate in the engine, taking up space that is usually important for the fuel and air to mix properly. These deposits can raise the compression within the cylinder, which can cause pre-ignitiion and thus, knocking. A more obvious reason is using a low RON number fuel in engines that are designed for higher compression and require higher RON fuel.
For regular passenger cars, most engine have a relatively low compression ratio – in the case of the Saga, the 1.3 litre VVT engine has a ratio of 10.1:1. The usage of RON 95 will not result in any engine knocking, even if you used RON 97. It is always recommended to follow the factory-suggested fuel type for your engine, which should provide optimum levels of performance.
Consider this, if you’re working in an office and barely take part in any sporting activities, should you suddenly decide to eat like Usain Bolt, will the sudden change of diet immediately turn you into an Olympic sprinter? Not likely. Unlike a human being that can be trained to be one, you can’t force your car to continuously do sprints and one day hope it accelerates like a sports car, even with RON 100 but that’s a story for another day.
What type of engines have high compression? Normally, high-performance ones that are naturally-aspirated like the K20A DOHC i-VTEC from the Honda Civic Type R (FD2), which has a compression ratio of 11.7:1. Mazda’s SkyActiv-G engines are an example of high compression engines found in non-high-performance cars (14.0:1 in the Mazda 2), although they have been tuned to accept RON 95 and above fuel.
Another example are NA engines that have been modified by skimming the cylinder heads, which in turn provides a higher compression ratio – a common practice among car and motorcycle tuning garages. On the other hand, turbo- or supercharged engines have lower compression ratios (9.6:1 in the Volkswagen Golf GTI) as a higher compression ratio and boost from forced induction can shorten the life of the engine.
Most modern engines are equipped with a fuel injection system that come with sensors that are capable of detecting engine knocking, and can then adjust the engine’s spark ignition timing to “fix” the issue. In the process of doing so, the engine may not operate in the most optimum manner, which can result in power and efficiency losses.
Aside from this technical explanation, Mohamad Hafiz Abd Aziz, product technician at Petronas explained that there are plenty of factors that affect a car’s fuel consumption.
“To determine that fuel consumption of a vehicle, there are other factors that affect it aside from the type of petrol used. For example, the car’s engine management system, amount of weight carried, tyre pressure, traffic conditions and others. Generally, if we’re focusing on cost savings, I believe RON 95 has an advantage.
“The results obtained from the test of both Proton Saga 1.3L cars, with the difference of 3 sen per km between the unit using RON 95 and RON 97 is deemed as a normal reading and expected from both types of petrol,” he explained.
“On the assumption that using RON 97 will provide better driving performance and a further range, there is some truth to it. In terms of performance, certainly. However, looking at it from a cost standpoint based on the amount of ringgit spend per km, RON 95 would provide better savings to users, especially when the price difference is 30 sen per litre currently,” he added.