[COLVERT]

Originally Posted by marinabrian

All of the petrol variants of our cars are tuned in the UK to use 95 Ron fuel, there is absolutely no benefit whatsoever in using 98 Ron fuel, the car will not run better, you will not become irresistible to the opposite sex, and your car will not do an extra 50 MPG.

Higher octane fuel is less prone to pinking............so if you need to fuel your P6 V8 with five star, then you can still buy "real" petrol from BMH.



Back to the here and now, other markets are tuned for lower Octane fuels, Australia for instance use 92 RON fuel, and their "premium" fuel is actually 95 RON

With the low mileage cars, I leave only a small amount of fuel in there, and when pressed into action, fill as required as modern fuels tend to go stale when standing, due to the ethanol content as required by the EU,being both hygroscopic and having a tendency to evaporate off, this of course applies to both 95 and 98 RON fuel.

Another fact, the higher the octane rating, the higher the temperature of the spark required to ignite the mixture, this is why the ignition system of cars running LPG need to be in top condition.......incidentally LPG is circa 110 RON, however the calorific value is lower than petrol, so you have to burn 20% more to achieve the same output.

It's not all about octane either, a little light reading HERE

Brian

Yer.---



Now for the chemistry lesson: Oil is a hydrocarbon fuel, meaning the individual molecules contain carbon and hydrogen atoms chained together. Modern petrol is blended according to various recipes, the active ingredients for which include about 200 different hydrocarbons, each with a spine of between 4 and 12 carbon atoms. One of them, isooctane, consists of 8 carbon and 18 hydrogen atoms (C8H18) and is exceptionally resistant to exploding spontaneously when exposed to the heat and pressure found inside a typical combustion chamber. Another, n-heptane (C7H16) is highly susceptible to such self-ignition.

These two compounds are therefore used to rate the knock resistance of all petrol blends. Petrol that resists knock the way a mixture of 87-percent isooctane and 13-percent n-heptane would is rated at 87. Racing fuels with octane ratings over 100 resist self-ignition even better than pure isooctane. The octane ratings for regular-grade fuel range from 85 to 87, mid grades are rated 88 to 90, and 91 and higher is premium.