[Mindgrinder]

as per many reviewers and experts always keep a 2:1 ratio for a normal car.

That is 2 fills for regular fuel for 1 fill of high octane.

[devrajman]

Regular or Premium gas. What octane should YOU use ?


Basic technical details that will allow you to decide what octane is best for your car

Some facts and myths about using Regular v/s Premium gas. When it helps to use high octane gas and when it does not.
There are reasons why high octane fuel is often given names like "Super" or "Supreme" or "Premium", but more power and/or more gas mileage are not one of those reasons!
Let's bust a myth first - "High Octane oxygenated fuel has more energy". Higher octane oxygenated fuel has actually LESS energy per unit. It is really the design of the engine that can take advantage of a particular characteristic/property of high octane fuel which allows the engine to produce more power. If your engine was not designed for premium fuel you are just wasting your money.

To really understand the difference between the fuels you need to first understand some basics about how engines work and what role octane plays in the process of making power.

A car's engine produces power by combustion. A compressed mixture of fuel and air is ignited by a spark plug. This ignition and thereby combustion needs to happen accurately at a very specific time. Sometimes the combustion does not happen at the right time - it ignites even before the spark plug has a chance to fire because the compression itself has produced enough heat to ignite the mixture. This is called pre-detonation or knock or pinging and is very harmful to the engine. Prolonged knock can ruin your engine in no time.

The amount of octane in your fuel determines how far the mixture can be compressed before it pre-detonates. Higher the amount of octane the lesser is the risk of pre-detonation due to compression. And that's about it. Higher octane by itself has nothing to do with more energy or more power or better gas mileage.

Now, in general an engine with higher compression is capable of producing more power. There is a limit to how much compression you can design in the engine before you hit pre-detonation for a certain amount of octane. If you want to go for higher compression you need higher octane, so to allow the use of higher compression, higher octane fuel was introduced. As a rule of the thumb (and you know thumbs come in different sizes) any cars below 10:1 compression ratio can use regular octane (87) fuel without a problem and anything above 10:1 could use high octane fuel. You can find the compression ratio of your car in the owner's manual spec section.

So what does this all mean to YOU in the real world ?
If you have a car designed to run on 87 octane, it can't take advantage of the benefit that higher octane fuel has to offer. So there is nothing to be gained in terms of power or mileage if you use premium fuel. The only effect would be a lighter wallet! In fact you might loose some power and mileage. Remember I mentioned at the beginning higher octane has less energy per unit ?

If you have a car designed to run on high (91/92/93) octane, then use high octane fuel. If you use low octane fuel, the engine will experience pre-detonation and as a safety measure the car will adjust to lower octane fuel i.e. it retards timing. Without going into too much technical detail, in simple English it just means you loose power and mileage. Not just that, you risk damage to your engine. Modern engines are quick to detect pre-detonation (even before you can hear it!) and retard timing but you still are putting your engine at a risk.

So just go with the manufacturer recommended fuel. Don't experiment. The only exception to this rule would be a really old engine that has a lot of miles on it. As carbon accumulates in the combustion chambers compression ratio rises. So a car that has a compression ratio of 9:1 when new could probably have a compression ratio of 11:1 after 75,000 miles. So now which octane do you use ? J Well first of all I would decarbonize the engine but if that's not an option, the engine could benefit from using higher octane fuel.
Another plus of "premium" fuel is that some (not all!) brands of premium fuel have better additives (than their regular fuel) to help keep your fuel system and injectors clean. That does help in the long run.

Worried about your spending for Premium fuel when cost of gas is so high ? Have you noticed no matter what the cost of gas is, the price DIFFERENCE between regular and premium fuel always stays the same ?

[thedreamcatcher]

It is always better to use normal fuel. The premium fuels contain certain additives which can damage the engine in the long run.

There was a good program on NDTV which highlighted this

[equinox22]

I believe one should fill what the user manual of the car states. If its not mandatory to fill premium fuel then its just a waste of money. In fact some cars run worse on higher octane fuel than regular. However if you engine is tuned for high octane fuel then it is a must to fill only premium.

[aerohit]

Here is my story - opposite

I always Premium fuel in Swift, for many years now, and car runs good.

Sometimes when I use normal due to non-availibility of Premium, i can easily feel like car is running on empty-water-papad engine. It feels like crap!

I have to agree that the swift 1.3 petrol is totally unrefined for present times.

[carboy]

Originally Posted by aerohit

Here is my story - opposite I always Premium fuel in Swift, for many years now, and car runs good.Sometimes when I use normal due to non-availibility of Premium, i can easily feel like car is running on empty-water-papad engine. It feels like crap!

Psychological - you are paying more money. Hence you feel it is runningbetter. This is pretty normal.It's like people buying expensive wires for audio systems & feeling that it improves the sound.

[tintin82]

Most manufacturers who sell cars in India natively tune their engines and program their ECU's to work optimally on regular fuel. And that's the reason why the manual recommends regular fuel instead of premium fuels.

In most cases, premium fuels do not give any performance improvements or mileage directly, instead it's mostly the additives that reduce carbon deposits and lubricate the chambers better that makes one believe that there's better FE and performance.

So basically, if you have the dough in the wallet, tank her up with premiums, if not, settle well with regular fuel. But one aspect to remember is to stick to a type of fuel and don't juggle around with different types. If you decide to use speed or Extra Premium, stick to it unless you don't find a drop of it around.

[Atlblkz06]

Premium fuel isn't "premium". Its just different. Higher octane is necessary for cars that require it, and a complete waste in cars that don't. It doesn't even qualify as "cheap insurance".

The only way to "prove" any advantage is on a dyno. Your seat-of-the-pants feeling will lie to you every single time!

[sgiitk]

I think the situation also depends on whether you are in a Euro II or Euro III city. In a Euro II city normal petrol is 87RON while E-III petrol is 91RON. IOC-XP is 93RON. Other premium fuels RONs are not specified. I am keeping 97RON out of this discussion since it is far more expensive.

A colleague did extensive tests in his Baleno (EIII city) and came to the conclusion that Premium given about 5% better economy, and a smoother running engine. As teh price difference is also about 5% so there is no loss in running premium.

I run premium in both my cars.

[Sprucegoose]

I got an OHC type 1 1.3 exi & i use only IOC XP,

not noticed any performance improvements over any other fuel, but the car runs slightly smoother.

or so i like to tell people

[VeeTee]

The higher octane (petrol) or cetane (diesel) rating fuel by itself shouldn't help fuel economy since it is to ensure knocking doesn't occur. Do these "premium" fuels have any other additives along with the higher rating to enhance the fuel economy/ ensure better running of the engine?

[dadu]

Originally Posted by VeeTee

The higher octane (petrol) or cetane (diesel) rating fuel by itself shouldn't help fuel economy since it is to ensure knocking doesn't occur. Do these "premium" fuels have any other additives along with the higher rating to enhance the fuel economy/ ensure better running of the engine?

I dont think there is a difference in the Octane/ Cetane but premium fuels contain additives which help clean the engine and burns better. Only this helps the engine in improving the performance and no this is not a perception but a reality.


I am also aware that a lot of people will quote it damages the engine and the seals, this also is not true "NOW". To understand we have to go back into history, in the early 2000, when the premiums were introduced the equipment manufacturers realized that the aromatic contents of the fuel was damaging the seals of the fuel pump and related assemblies. This was due to the additive reacting with the material used in these seals. The OEM's changed these to a newer material which didnt react/corrode and then all was well.

Rest all are rumours nothing concrete.

[Harbir]

Originally Posted by devrajman

If you have a car designed to run on high (91/92/93) octane, then use high octane fuel. If you use low octane fuel, the engine will experience pre-detonation and as a safety measure the car will adjust to lower octane fuel i.e. it retards timing. Without going into too much technical detail, in simple English it just means you loose power and mileage. Not just that, you risk damage to your engine. Modern engines are quick to detect pre-detonation (even before you can hear it!) and retard timing but you still are putting your engine at a risk.

Not entirely complete. This differs depending on whether your car is premium "required" or not.

If the car says "required", then you have to use it, or if it not available, then you have to treat the engine very gently till you can get higher octane fuel.

If it is not required, then there are two possibilities.

1. engines that should be fed regular because they neither need nor can they take advantage of premium.

2. engines that are perfectly happy with regular, but if fed high octane fuel, can provide maybe 1% to 2% more hp.

If your engine is of #1 kind, then feeding it premium is just a waste of money. If it is of the #2 kind, then its up to you how much premium you place on getting 1 to 3hp more.

I have a Lotus Elise that use premium only, what with it running 190hp from 1.8 normally aspirated litres. I have an MX-5 that was fine on 87, but on which I advanced the timing for better crisper throttle response and a bit more power, but now it needs premium to run cleanly. And I have a Honda accord that runs just fine on regular, which makes more power than I use 99% of the time, but will make maybe 4-5 more hp if fed premium. but seeing that I rarely use its performance and that the mileage barely changes, I feed it regular only.

[carboy]

Originally Posted by Mindgrinder

as per many reviewers and experts always keep a 2:1 ratio for a normal car.

That is 2 fills for regular fuel for 1 fill of high octane.

Keep away from these experts.

[Atlblkz06]

^^ I agree, keep away lol.

Keep in mind that Europe (and India?) use the RON (only) method and others like the US use the (R+M)/2 method. So 87 Octane in the US is the same as 91 in Europe and India, and 93 here is the same as 97 there.

Ron = Research Octane Number
Mon = Motor Octane Number (derived through measurement in an engine)
Pon = (R+M)/2