So is it a myth or a fact that hi-octane increases horse power and improves gas mileage? Well the one word answer to the question is yes, it increases horse power of your engine. But unfortunately the matter is not that black or white. There are a lot of factors, including the motor of your car, effecting this fuel-engine match.
What is hi-octane?
The octane requirement of an engine varies with compression ratio, geometrical and mechanical considerations and operating conditions, like temperature and load, etc. Octane rating are usually measured in RON, which stands for research octane number, it is a rating used to measure knocking resistance in spark ignition internal combustion engine.
What does it do?
In a cylinder, when a piston pushes the air fuel mixture in compression stroke, the spark plug ignites the combination of both which results in the piston being pushed back down. This is an ideal situation where the engine is following proper movement.
In an engine knock condition, the piston pushes the air in the cylinder and the air fuel mixture temperature gets too high that the fuel combusts on its own before the spark plug is set to ignite. Similar mechanism is in the diesel engines where there is higher compression without the use of spark plugs.
Higher octane provides for less of a chance of pre-ignition of fuel which causes knock. In a normal situation, the fuel only ignites when the spark plug lights up which is the proper movement for an engine. The car engine is likely to get damaged or will run less efficiently in a knock situation.
Which engines require hi-octane?
Many of the modern high compression engines or engines that use forced induction (turbo charged) require premium fuel, meaning fuel with higher than your average 87 RON. The reason for this is that: As the compression ratio of an engine increases, the chance of knock increases as well so higher octane prevents the knock from happening. In this case, putting a lower grade of gas will cause knock to become apparent and the engine computer will make changes to prevent the level of knock.
Octane ratings in Pakistan?
Octane ratings in Pakistan are even lower in premium fuel compared to those in other countries. It is like when they say premium unleaded has 87 RON, you can expect it to be normally less than that, and what your manufacturer recommended fuel is usually 87 RON. So there are chances your car won’t perform up to its mark and will experience engine knocking, where as hi-octane in Pakistan is said to be of 91 or 92 RON according to couple of people attached with fuel business, although PSO website states its 97 RON, which is quite good frankly, but I would take that number with a pinch of salt.
But does my car need hi-octane?
Now, you can argue that since petrol in Pakistan is not exactly of good quality, you are better off running high octane fuel. But the question is; what are your driving needs? If you are running a run-of-the-mill 4-cylinder family sedan (whether new or old), you can be assured that you do not need to spend an extra on fuel by filling hi-octane. And even if you think, your super duper 1800 cc car deserves better, then new cars are well equipped to run the fuel you find at your normal petrol station.
How to tell how my car is performing on hi-octane؟
The very crude but effective way to find how is your car doing on the normal 87 RON petrol is: Simply inspect your engine’s spark plugs. If they are reddish/brownish in color, your car is doing well and, again, you do not need to spend extra on the fuel. You definitely need high octane petrol if you are running a motor with high compression ratio; for example Toyota’s 4A-GE 20V engine (both ST and BT). Those engines had high compression ratio and used to knock on our normal (regular) petrol.
And if you think you are going to get any performance from hi-octane fuel in your otherwise ordinary/normal car, you might be disappointed. First of all, there will not be as such any performance gains. And even if there are any, they will be so petty that you will not feel any difference. Although there are high chances that you suddenly start to think that your car has suddenly turned into a DTM car which may just be a placebo effect. Whatever gains there will be, they will be so insignificant that they will not be able to register them.
Local and Japanese imported cars?
Our locally manufactured cars are factory tuned to operate on locally available petrol. Imported cars however might be another story. Since most of the cars are imported from Japan, those cars are tuned for petrol available in Japan, and fuel in Japan is of excellent quality. Simply put, your vehicle might not benefit from using an octane higher than what your car’s owner manual recommends.
Is it worth the price difference between super and hi-octane?
Although you can argue that since hi-octane petrol burns far better than lets say a 87 RON petrol, you will get better economy. That again all depends on not only your vehicle, but also your driving conditions. And also, you need to keep in mind the price difference of normal super and hi-octane fuel. Before the major dip in oil prices all over, the difference between super unleaded and hi-octane was something like 30 rupees. That difference could easily off-set whatever excess mileage you were getting on hi-octane. Currently, the difference is somewhere near 6 rupees. So it all depends on you and your vehicle if the extra cost is worth it or not.
Hi-octane in a performance car:
In a performance (sports) car however, the story is different. A turbo charged or supercharged gasoline engine, the compression ratio is customarily built at 10.5:1 or lower. This is due to the turbocharger/supercharger already having compressed the air considerably before it enters the cylinders. Port fuel injected engines typically run lower boost than direct fuel injected engines due to the fact that port fuel injection allows the air/fuel mixture to be heated together which leads to pre-detonation. Conversely, directly injected engines can run higher boost due to the fact that heated air will not detonate without a fuel being present. In this instance, they inject fuel as late as 60 degrees before top-dead-center to avoid heating the mixture to the point of compression ignition. Engines with higher compression ratios have advance engine timing and so they run perfectly on hi-octane and will knock on a regular fuel.