View Full Version : Unleaded / Super Unleaded fuel

02-02-2001, 20:42
Some notes from a discussion with Millers Oils.

Unleaded and Super Unleaded appears to have a shelf life of six weeks before it starts to lose octane rating, due to evaporation of the volatile additives. This is from manufacture at the refinery, so fuel is already ageing before it reaches the forecourts. Thus I was advised to buy fuel from a high throughput garage which turns over its stock quickly(say, in under four weeks). It follows that Unleaded is more likely to be consistent than Super Unleaded, unless the Super Unleaded sales are high at that site. They recommend avoiding Supermarket sites (as the fuel is barely 95 rating), rather use main BP, Shell etc. sites as this is 95 |PLS| rating.

Of course, Millers have an interest in our using Unleaded and double quantities of Millers CVL additive to boost octane rating by 6 points, however what they say makes sense to me. Tuning is all about knowing just how near to the edge you can go e.g. with ignition timing, and consistent minimum fuel octane rating must be good news.

It follows that when I park my Evo Rallycar up after an event with half a tank of fuel, the octane rating will drop as the car stands. The same will apply to any Jerry cans, unless they are brim-full. Thus I need fresh fuel in for each event (a good excuse to run around before the next event and empty the tank!)