petrol

[lotusolly]

I have tried running the car on optimax and BP ultimate and not really noticed any difference in the cars performance.
A friend of mine recommended trying Sainsburys super unleaded.
I have not usually gone for supermarket fuels but having tried it I can say I noticed an improvement in performance and a smoother running of the engine.
Has anybody else found preferable fuels?
Does anybody know who supplys sainsburys petrol and where else it can be brought?

Olly

[amar_fiaz]

In my experience i have found optimax to be the least satisfactory petrol (surprising, considering all the investment and advertising it has). I found it made driving a real struggle, in fact the clutch felt heavy and gear changes weren't so smoothe (strange, i know!!).

Anyway, of all the priemum brands i prefer BP Ultimate to be the one i preferred. But then as an experiment i went with 'normal' octane fuel from the leading garages and i must say it all seemed the same as BP Ultimate!!

What are your experiences of these fuels, does everyone recommend that 97 RON fuel be used in the NSX??

[MattS]

My Saab turbos definitely run smoother, quieter and faster on Shell Optimax...BP Ultimax (or whatever it's called) is quite a bit more expensive in these parts, so I don't tend to buy it. Super unleaded from the supermarkets seems to have much the same effect as Optimax in the Saabs at least.

I haven't got an NSX yet (pls see my post in general discussion), but maybe next week....!

[ctrlaltdelboy]

unless you have a programmable ECU to enable you to tune the car to take advantage of higher octane fuels OR to tune it to run satisfactorily on lower octane fuels, you are very much shooting in the dark or simply judging differences 'from the seat of your pants'.

if you do have a programmable ECU or some method of monitoring knock you will be able to get a more accurate flavour for which fuels are 'better' in terms of octane than others.

the term octane itself is widely misunderstood and even more widely misused or mis-stated.

a true octane rating is that which is used on the pumps in the USA - these ratings are lower in numeric value than the equivalent 'octane' ratings used in the UK.

in the UK we work on RON values (Research Octane Number), the other number which is more important than RON but is usually overlooked is MON (Motor Octane Number).

a proper octane value is (RON+MON)/2

the most important benefit of a higher octane rating in fuel is that it can mitigate/reduce detonation (knock) - wherever you are able to prevent knock you are also able to run higher boost levels (in FI engines) and more advanced timing in order to create more power - these power increasing measures would otherwise also create engine destroying levels of knock.

the reverse of the above benefit is this - if an engine (eg JDM) is designed and tuned to run on a higher octane fuel than it is actually running on (Japan has 100 RON fuel but we have only 97RON), knock may come into the equation where it would ordinarily have been absent - this is an extreme example, but anytime that an engine is run on a lower rated fuel than it was mapped for there will be a performance degradation - this is what is most commonly posted about in 'octane rating' discussions.

hope this helps


p.s. if you are really interested in this subject (then you're as much of an anorak as me) and you have plenty of spare time, take a read of this thread
http://www.gtr.co.uk/forum/upload/showthread.php?t=2480

it was started in May 2002 and is still being contributed to today after 357 posts and counting!

[Welshman]

Don't forget that all petrol in this country comes from one of four refineries so all that can differ is the additives introduced by the oil companies. Odds are that Sainsbury's super unleaded which is quoted at 97 RON is probably BP Ultimate.