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Which Petrol do I Use for my Car & What do Those Numbers Mean?

There is a bit of a mystery that petrol companies deliberately play to confuse the unsuspecting public about what is the right petrol to use for your car.

The petrol companies perceive that using a higher number octane will give you more power and better fuel economy. This is actually false!

High octane petrol cannot give you magical higher horse power unless your car’s engine is designed and tuned to take higher octane rating. So a normal 4 cylinder engine will not benefit from high octane fuel.

What is Octane? Please explain?

Octane ratings are not a measure of energy or power, but instead measure the point when a normal controlled fuel burning (propagation) inside the engine cylinder goes into a uncontrolled burning (detonation).

The picture on the left shows a smooth burning transition when the spark plug fires. The picture on the right shows pre-ignition that is the fuel igniting from excessive heat, when the flame fronts from the spark plug collide from the flame front of the pre-igniting source – its’ similar to a hammer hitting your engine. The result is possible internal engine damage – the term is referred as engine KNOCK.

Petrol companies can measure this knock and add anti knock agents like Toulene, Triptane, Isooctane to name just a few to increase the engine octane rating. Ie unleaded 91 to unleaded 95 add a bit more agents we have 98. These agents retard the rate of fuel burn, slowing the flame propagation down also eliminates pre-ignition.

E10 uses a sugar based ethanol which also works as a anti-knock agent.

How does Octane work properly and what are the benefits?

The basis of making horsepower is air. The amount of air entering the engine cylinders is then compressed by the piston, fuel is then added by the injector and ignited by the spark plug. The amount of air added is in direct proportion to the power made. Turbo chargers, super chargers, high lift camshafts, big valves, cold air intake, bigger throttle bodies are all in direct relation in getting more air into the (engine) cylinder hence the more air then more fuel is added and bigger bang. BINGO. MORE HORSE POWER! BUT WITH MORE HORSE POWER WE HAVE MORE HEAT, WHY?

The more air added to the engine has more air molecules rubbing and compressing against each other. This causes friction &friction causes heat.

To overcome this heat from detonating the fuel, Petrol companies have brought out fuel with higher octane levels to compensate the tendency for fuel to pre-ignite in a compressed state. The other benefit of higher octane is that car tuners whether that be in the factory or aftermarket can extract more ignition timing in a controlled state hence benefiting in extracting more horse power from the engine. The V8 Supercars take E85 which has a even higher octane rating of 105.

It is very essential to know what type of fuel your car requires. If it’s a sport model like a highly tuned Honda, Toyota and European sports, supercharged, turbocharged cars, chances it will probably take some special octane fuel. For any enquiries please call Manny’s Mechanical Repairs.

Manny’s Mechanical Repairs specializes in tuning, we have the latest diagnostic equipment, scanners, labscopes and dyno tunning gear to ensure your vehicle is tuned and running at it full potential.

– Manny, 0411 496 621
To serve, to perform, to guide.


At Manny’s Mechanical Repairs you are in good hands, our main services include, Safety CertificatesLogbook ServiceFree Pickup & Delivery, and Car Cooling System Repairs.

We have the latest diagnostic equipment and my work van is fitted out with an industrial air compressor. This enables me to perform heavy duty work and give you – the customer – the best service at any place and at any time.

For Bookings and enquiries, please contact us on 0411 496 621email us at or visit our site