At the risk of opening up a long and well rehearsed debate about after market fuel additives:-
I have experimented with using pure Acetone (what most people recognise as being nail varnish remover) as an additive in my 19 year old motorbike. Dosage 50 to 60ml of pure acetone per 10 gallons.
Results:-
although these may be psychological, I do feel it has made the bike run smoother (FJ1200's do vibe a lot), and I am quite sure I get a few more mpg (5mpg more touring france for 2 weeks than the year before) although that could be down to many, many different factors. It has certainly not done any harm (a year in trials), although my bike is a carb fed fuel system without all the modern electric fuel gizmo's in a mega.
Do a google for "Acetone as a fuel additive", there's reams of talk about it, some sceptical some not. But I am sure Which magazine did a report on the aftermarket stuff like redex/STP etc and they found they made no difference at all to performance or mpg, although those tests were no doubt done on a clean engine. So as someone mentions above, a dirty fuel system might benefit quickly in the short term from a clean out.
Warnings:-
do not use acetone/nail varnish remover from a beauty store. For one it is vastly expensive; and 2, it contains moisturisers/softners such as lanoline for nails which will react badly with the combustion and produce nasty results in the internal fuel delivery system. If you are going to do this you must get 99% pure stuff.
I bought mine from this company below £8 per 5 litres, although postage was steep (highly combustable liquids in large quantities) so they phoned me to ask if i really wanted only 5 litres. So I bought 10 litres (economies of scale as the postage was the same for twice the amount etc.).
http://www.allscotltd.co.uk/prodtype.asp?strParents=&CAT_ID=123&numRecordPosition=1Someone on ebay is selling 500ml as here.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250306806761&cguid=1189496211d0a0e202c3d983ffe5f916It has other usages too, paint stripper, general degreasing agent, sniffing (oops, did I say that!).
Some say that Acetone will degenerate rubber fuel hoses, but at the dilution used above it is very unlikely. Having said that I have not tried it in my omega yet..
Re Tesco Petrol. I have read that although most petrol is dispensed from the same tanks at each refinery, the refiners/wholesellers, add additives at the point of dispensing depending upon the buyers (i.e Tesco's or your local independants) requirements. And the reason why Tesco's petrol is cheaper is that they order less additives. So some additives to Tesco's petrol might give improvements in mpg, but Redex I would say is a very expensive way of doing it.
Not to say that Tesco's petrol is bad, but I read that BP Ultimate for example uses Acetone as one of its additives to improve combustion (Acetone breaks down the molecules or surface tension in petrol thereby theoretically giving improved combustion). Which may be why BP ultimate is regarded quite highly by some (although again you are paying way over the odds for BP to add in their requested additives).
Profit at every stage!
You pays your money and takes your choice.
By the way I believe any change in petrol and its additives takes some time for an Omega's brain to work it out, so any improvement that these additives may have are certainly not instantly recognisable. May need a few hundred miles for the sensors to react and the brain to adjust - but I might be completely wrong.
Mark