Octane ratings are referred to in one of three main units of measurement: Research Octane Number (RON), Motor Octane Number (MON) and Anti Knock Index (AKI). Most of the world uses RON ratings, yet USA and Canadian drivers use fuel rated by AKI. This is essentially a mix of RON and MON. Due to the fact the MON test is much tougher than that of RON (the former awarding fuels an eight to ten-point lower rating than RON), the overall rating of AKI is close to five points lower than RON. Got it?!
In simple terms, the higher the octane rating, the more resistant the fuel is to what spannerwielders refer to as knock, detonation or pre-ignition. Basically, this is the point at which the heat and/or pressure in the engine cause the air/fuel mixture to ignite before it’s supposed to. Pre-ignition can cause serious harm to an engine, sometimes resulting in catastrophic mechanical failure. Melted pistons, blown head gaskets… you name ‘em, pre-ignition has caused ‘em!
It’s desirable to use fuel with a high octane rating when working with petrol engines, but contrary to popular belief, unless the engine is mapped for higher octane fuel (many modern sports cars utilise fuel management software to this effect), power won’t be increased by any significant amount. Conversely, if an engine has been mapped to take advantage of higher octane fuel than what it is you’re paying for, then you’re encouraging decreased performance and complaints regarding reliability. As we’ve said previously in Performance
Vauxhall, don’t think that running your Griffin on your local supermarket’s unleaded petrol and then only topping up with higher octane fuel the morning of your dyno day is going to bring you big bhp.
Using higher octane fuels allows you to increase an engine’s resistance to pre-ignition, thereby enabling the use of higher compression ratios, higher boost pressures and more advanced ignition timing, all of which help your modified Vauxhall’s engine to produce more power.
It’s also worth noting that while simply adding higher octane fuel won’t provide meaningful power increases unless the host engine has been mapped accordingly, potent petrol can help with reliability by increasing the ‘buffer’ before pre-ignition kicks in. It’s with this in mind drivers often add octane booster or higher octane fuels when using their cars at the track, where an engine is subjected to prolonged bouts of aggressive use.
If you’re going to retire your car from the road, be sure to use up leftover fuel in the tank