I've just filled up at my Local Shell Garage and they have a big promotion on their new unleaded Petrol. I can't remember the exact name (Optimax or something similar) which shows up either their promotion or my attention span. The flier made some wild claims about improved performance and that it replaced super unleaded as well as normal so I assume it is a higher Octane than normal unleaded. One of the main claims was that it would help you accelerate out of danger faster in "a typical family car". It also keeps your engine cleaner and reduces fuel consumption. It sounds like some of the wild claims made in the past for petrol additives / economy devices, surely they can back up some of these claims? Of course it's about the same price that Super Unleaded was but as it claims to cure most ills they obviously think we will buy enough of it
Robin
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www.shell.com/uk-en/directory/0,4010,44845,00.html for details.
Looks like an ultra low sulphur, super unleaded fuel, with a higher octane rating (98+) than usual super unleaded (97 octane). Ideal for cars with knock sensors that can benefit from higher octane (increased performance and better fuel consumption but 5p/litre dearer). I doubt whether cars without knock detectors will get the benefit. I know that some mercs, most bmw's, and the 105bhp 1.6 golf, all have knock detectors, not sure who else has?
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I thought octane rating was measured in relation to compression ratio. There is said to be a test engine somewhere with an adjustable compression ratio, used for determining a specimim sample of petrol's octane rating.
Retarding the ignition timing is just a poor way of compensating for a low octane rating. If a car has a high compression rating it will never run perfectly simply by retarding the ignition - it needs a higher octane petrol.
An alternative, as has been done in the past in times of poor petrol availability, is to lower the CR by inserting a thicker head gasket. This enables the engine to run without knocking, but at the expense of lower power.
Cliff Pope
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I thought all cars had knock sensors now. The point surely is whether the compression ratio is high enough to need higher octane petrol. I have always understood that once an engine's basic requirement for a given resistance to knock is satisfied, ie the octane rating is high enough, then there is no advantage in using petrol of a higher rating. Indeed, I have heard that too high an octane rating can cause the engine to run hotter - I remember from the days of cars designed to run on 2-star that 4-star could cause overheating.
Cliff Pope
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no, its not the comression ratio, it's the timing in relation to the octane of the fuel. Lower octane fuel will pre-ignite (pinking or knocking) earlier, thus the timing must be retarded to prevent damage. Higher octane fuel pre-ignites much later and the timing can be advanced accordingly which increases efficiency in terms of power output and fuel economy (although not usually both, depending on your driving style). A knock sensor, effectively, advances the timing automatically and you feel the benefit. Without a knock sensor, the timing remains set for 95 octane and little or no efficiency is gained.
Knock sensors are not common at all on today's cars. Most appear to be set up for 95 octane (premium unleaded), will tolerate 91 octane occasionally, but will not benefit from 97 or 98 octane.
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If Optimax is the same as in Germany it is 99Ron and will be of huge benefit to anyone owing and driving any German built car of more than modest performance. All German and Italian performance engines are designed to deliver optimum performane on petrol of 98Ron plus, which we did not previously have in the UK. German manufacturer performance, fuel consumption and CO2 emissions figures are achieved on petrol of 98Ron +. Run a BMW 330i on UK 95Ron petrol and you don't get anything like the 231bhp it delivers on 98Ron plus. Many owners of older cars (Cavaliers, particularly, which have a switch for 95 or 98 Ron) benefit enormously from higher octane petrol because they get better performance and better economy. In some cases it can work out cheaper to run on higher octane petrol, despite the higher pump price.
HJ
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The web site decribes the Octane as higher than 98Ron and suggests its has been released in other countries previously, so in the case of my wife's Astra (2.0i 8 valve) it would be worth changing the plug to 98 and running on Optimax? I realise that it's probably best to run through a tank first before changing and then sticking to this brand exclusively. The notes also detail the cleaning properties - am I likely to cause problems with a 7 year old engine that's only done 34000 miles?
I assume on my Vectra (1.8i 2001 model) it automatically senses the Octane and adjusts the timing accordingly - thats what it says in the manual anyway.
Robin
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I think you are right Cliff, hence the new shell fuel is good news, but only for those people lucky enough to drive a car that can adjust it's timing accordingly. Its the fact that rather than fit knock sensors, manufacturers retard the timing in the programming of the ignition system that means most cars cannot realise their full potential. The manufacturers are just playing safe, running on higher octane does no harm but running on lower octane can cause engine damage. A knock sensor is the best bet because it will retard the ignition to the most efficient point for the fuel regardless of its octane. If only all cars had one. Fortunately, my german car does have one and I am looking forward to trying the new stuff.
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Presumably this stuff will benefit the older cars whose manuals specify 98 octane, even if lacking some of the fancy modern management gear.
Incidentally, the Yamaha Turbo bike of about 15 years ago had a knock sensor - one of the first?
Cheers again, Alex
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Robin, yes, your wife's astra can be set to 98, assuming you can always fill up with optimax. Cannot think of any detrimental effect of the cleansing properties. Have you tried either your vectra or the astra on super unleaded? I know it is 97 octane but you would still get improved performance. You will have to calculate for yourself whether it is self financing through improved fuel consumption v increase cost per litre. Personally, I have always found the cost to be neutral with the improved fuel consumption offsetting the extra cost but have noticed big variances in the price of super u/l over premium. I expect to pay 5p extra but some garages charge 10p extra, so keep your eyes peeled. I always use super because the car feels better to drive.
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Yes, I have been using Super Unleaded in my Vectra for the past 3 months but have not really noticed a great deal of difference, partly because I had a 2.0 Vectra previously and find this one underpowered in relation anyway. I had a recent experience with contaminated petrol (see previous thread) and wondered if that was due to the super unleaded pump not being used regularly. Price isn't a problem with mine luckily as it's a company car and the Astra only get's filled up about once a month to 6 weeks. As long as I can convince the wife to pay another 5p a litre everytime I'll have a go with the Optimax in both cars. If I tell her it'll improve the performance she'll be all for it - she says she needs something to liven up the performance and I'm sure she was talking about motoring!
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The Shell website has the fairly obvious URL of www.shell.co.uk It tells us that Optimax has a very good detergent package, is higher octane than 98Ron and burns earlier and more completely in the combustion chamber, giving better accelleration, better economy and lower emissions. It also says that Optimax will be comparable in price to Super. So it looks like we have finally got the same stuff as the Germans about nine months later. Maybe Andy Bairstow can tell us more.
HJ
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I recall shell bringing out the performance petrol to end all performance petrols in the mid 1980s. Vauhxalls in particular where very badly effected with burnt valves I think. I ran my Harris Magnum motorcyle on it (M.Cycle F1 tune engine) I needed the vavles grinding after only a couple of thousand miles and that was with stainless racing valves with a lower 9.5:1 comp for road use rather than the 11:1 for track. Lets hope this isnt the same, I personally will wait to see how it goes.
Bill
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I used the same petrol, and needed a new engine shortly thereafter (Sud Sprint) and remember plenty of bad publicity, not just Vauxhalls. Coincidence?? Whatever, I haven't used Shell since.
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