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Old 27 Oct 2008, 09:45 PM   #1 (permalink)
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Superunleaded

Have been searching for petrol stations in my area regarding super unleaded. Found this (apologies if it's already been posted in the past)



Scanned from October 2002 edition of Mini Magazine.

By Keith Calver, Technical Wizz / Editor.

“My relatively recent decision to return to circuit racing has spawned furious activity in my 'grey cells' department on all associated topics, not least of all the engine build. Exploring which spec to run with, led me to thinking about the sort of compression ratio I could run within the regulatory control over fuels allowed. My research reminded me of a few interesting fuel-related details that may be of
interest to some of you. The subject mainly concerns fuel quality. I'm most certainly not going to be delving into the murky and incomprehensible world of chemistry, but the essentials make useful knowledge.
A vast majority of the fuel available on the UK mainland comes in from Holland. Yep, Holland. Not the Gulf States where much of the crude oil is drawn. The fuel distributor in Holland takes a sample from each shipment prior to dispatch to check for EU compatibility. If it isn't, he adds whatever he has and/or is cheapest in the chemicals allowed to meet the regulation standard.
This is the first problem because what is added is not always what is best for your engine — for example lead. The minimum quantity for this is way lower
than what's required to help minimise detonation.
Once happy, said distributor ships the stuff to Hull where it is then sold off to all the fuel companies. The likes of BP, Esso and Shell then take it to their distribution centres, recheck the quality and add what they see as the essential ingredients to bring the fuel up to their standard — which is somewhat higher than the basic EU stuff. Good news then for all those buying fuel from said companies. Some others simply take it to their outlets, then pass it straight on to retail fuel outlets where it goes straight into their forecourt tanks and then into
your cars. Hence why various forecourts offer cheaper fuel, no more expensive chemicals added.
This sort of fuel is OK in modern machinery with ECUs that are programmed to deal with varying fuel specs. But for your non-injected, possibly tuned Mini? Not good news. And it isn't a simple case of putting in fuel additives. Many of these simply make no difference as they rely on specific chemicals over a certain level of content per volume of fuel to create the necessary chemical reactions and, therefore, protection. For example: a lead substitute can claim to raise the octane rating of the fuel. If the fuel it is added to has the right level of a certain chemical (lead) in it, then it can work terrifically well because the chemical reaction needed can occur. If the fuel doesn't have the minimum level of lead it is unlikely to make any difference whatsoever.
Another issue is what the added chemicals do to the calorific value of the fuel. The internal combustion engine as we know it, creates heat to provide
power/motion. The greater the heat produced, the more power. The higher the calorific value of the fuel, the more heat is generated, the more power. Conversely, if the calorific value is diluted, power output is reduced.
Here's the shocker — far from super unleaded increasing power promised by it's higher octane rating, it actually has a lower calorific value than standard unleaded. How? A gallon of standard unleaded will have a certain calorific
value. To create super unleaded fuel, a certain proportion of chemical additives are used which have no or very little calorific value. The bad news is that this additive package is generally around 20 per cent of the volume — so now you only have 80 per cent of the original calorific value. Higher octane rating does not
mean higher power output. Just that it is less prone to engine-destroying detonation.
All bad news? No. While BP and Esso fuels are consistently better quality than many others, Shell Optimax is incredibly good for forecourt-available fuel with a relatively high calorific value and anti-detonation package. Let's hope the other big names get with the program and create their own alternatives. Those
lucky enough to live in North Yorkshire (ahem) and North Lincolnshire are better off than most, as Bayford Thrust (Thrust petrol stations) still sells good quality four-star fuel. And out of all the available octane boosters on the market, there's still only one that is guaranteed to raise octane rating, no matter what pump fuel it is added to — Aldon Automotives 100-plus.”
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