Premium vs Regular Fuel, do you really need it?

A fair question in anyone’s book and especially relevant these days as more and more cars “suggest” you use Premium fuel every time you fill up your car.

Is this the truth or just more nonsense from our car loving manufacturers in unison with the cashed up oil sheiks wanting to gouge us in the back pocket on a more regular basis?

Let’s take a look shall we…

I believe it can be stated that Premium fuel will give you a better performance out of your vehicle but it may only be around the 3% mark which means you won’t even be able to feel the difference.

Let’s delve deeper, so here we go, a little bit of “Engineering for Dummies”…

A high compression ratio is totally a good thing, in theory.

Expansion over a greater range during the power stroke means you get more performance and greater efficiency, so that’s awesome!

But there is a slight problem, fuel/air mixtures are not infinitely tolerant of compression.

At some point the mixture starts to burn spontaneously too early, and that’s what engine knock or pinging is.

Knock is when combustion goes off literally, half-cocked!

Engine knock at high revs and big throttle inputs can destroy your engine, so the designers do really try to avoid that, and sometimes they do that by using high octane fuel.

Octane rating is a scale that defines a fuels tolerance to compression, the higher the rating the more tolerant the fuel is to high compression.

Octane rating is an applied chemistry thing. There is a very particular kind of octane, the chemical called iso-octane, 98 RON fuel has the same not resistance as a mixture of 98% iso-octane and 2% heptane.

Adding confusion here is the 3 different flavours of octane we use around the world, RON is the Research Octane Number where the special test engine is run at 600rpm for the test.

Then there is the MON Motor Octane Number where the special test engine runs at 900rpm, so MON is always lower than RON by about 8-12 points.

And then there is the AKI, Anti Knock Index which is the average of RON & MON, so AKI equals RON plus MON divided by 2.

There are plenty of options out there when it comes to tinting with every Tom, Dick & Harry having their say on how much sunlight they can keep out of your car.

In most countries including Australia, RON is used routinely but in the USA, Canada & Brasil they use AKI, and the upshot is AKI is always about 4-6 points lower than RON.

This is important when you live in Australia and download a US spec for a car and take that as gospel, without knowing the different rating systems, as you might draw the entirely erroneous conclusion that standard gasoline is okay when in fact premium is required because an AKI of 90 is actually a RON of about 95, the Jeep Grand Cherokee is like that.

You should NEVER use a lower octane rating than the manufacturer suggests, NEVER but you can use a higher octane rating all day long.

Knock sensors are in your engine listening for that little knockity knock knock and every car has one. The high octane fuels will allow a little more “play” as it is more dense and can handle it marginally better.

If your cruising down the highway in your car sucking down 91 RON fuel and then you magically change to 98 RON fuel you might find that instead of sitting on 100km/h you might be on 105km/h, which as I stated previously, is due to the higher density in the 98 allowing more play and less knock.

From there if you ease back off the throttle slightly and cruise at 100km/h you would see minimal savings in fuel economy, key word is minimal.

Yes we all see the dragsters using high octane fuel and safely assume that must be what’s best for our little runabout but in essence, we don’t really need to be at work 0.452 sec quicker to know that high octane is best!

A dragster though is different, that 0.452 sec can be the difference between being Australian Champion and some guy who drives fast cars.

The other argument of gaining “more power” from your high octane fuel is crazy for your general Joe Blow, if you want more power you put your foot down on the accelerator and the power is delivered from your engine.

To know if your fuel is delivering you more power, you need to be at peak power in your car, which again, driving from Ashgrove to Fortitude Valley is probably not going to happen.

The one thing I will say about premium fuel is that it will clean your engine better than the regular stuff.

So you will certainly get better fuel economy on premium, but with the higher price of premium, you will end up paying more per kilometre.

So for most car owners premium fuel is a nice idea which will be better for your car.

My advice for average car owners is to run the fuel the manufacturer specifies, if you have a car that requires regular and you want to use premium, knock yourself out, all you will be doing is spending a little more money each time at the bowser but also protecting your car a little better over the long haul.

I will say if you car requires premium and you want to use regular, you will be spending a lot more time with your service department and they will be thanking you, over and over again!

For more information and a great job in explaining this better than I can, check out John Cadogan’s You tube channel.

His insightful, and at times “colourful” way of explaining things is not for everyone, but here at Brisbane Car Shed we love his views on all things cars!

BEWARE: John tells it exactly as it is, so if you are easily offended you may not enjoy his hard truths as John calls a spade a f%$#@ing shovel!

Remember if you’re looking for a new car or need to sell your current car, talk to me! Call Paul on 0411 362 229.