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Ive used Shell Optimax since day one on my 172. With an 11:1 compression ratio the engine in the 172 will run "below par" on less than 98 octane. The knock sensors will probably have a de-tuning effect on the engine to reduce pre-ignition. The CR on smaller 16V engines is around 10:1 so are less likely to pre-ignite. Putting Optimax in these engines will probably have negligable gains. My last Clio (1.6 16V Dyna+) also with a 10:1 CR would run ok on 95 and 98 RON fuels. However I reckon the Super Unleaded 97 RON gave a slightly better fuel consumption.
If the older members can remember when Shell launched their Formula Shell (circa 1988 ish). This used a sodium substitute for lead. My higher than average CR MKII 16 Golf then used to run sweet on this juice. It all crumbled when Vauxhall claimed that it screwed up their inlet valves?! Still think Vauxhall used this as a cover up for their sh*te engines.
Anyway, from all this, I reckon Shell are one of the pioneers in developing good forecourt petrol. The Asda/Tesco petrol may be cheap but will generally not give good performance / mpg figures. Optimax is probably the best fuel available at the present time. If you can aford it and have a higher CR engine ....use it!
No kdf, renault only recommend 98 ron to help the engine run cleaner (will not clog the fuel filter as quickly because there are more cleaning additives etc.. and during a yearly service you would normally get a fuel flush to help with this) due to the long 2 year service interval. There is actually no performance benefit using optimax or 98 ron on NA engines (like there is on a turbo engine) other than it cleaning the engine a little and maybe helping throttle response a little, which means nothing in the real world.
You would be better off using 95 ron 75% of the time and 98 ron 25% of the time, to just keep the engine cleaner.
Weyland, my Audi S2 turbo engine runs like a old Skoda on 95 RON with a fuel consumption of ~18 mpg? If I used the past 97 RON Super Unleaded or the latest Optimax 98 RON replacement the car goes like sh*t of a shovel and returns an average of 25 - 26 mpg !
BTW, Reno these days generally have 12K, 18K or 2 year sevices depending on the model, so are unlikely to get an "annual fuel flush" from Reno (which I doubt anyway). The fuel filter is likely to be changed during this service and is unlikely to be clogged up through using a lower octane fuel. Fuel filters are mechanical filters and generally pick up suspended solids in the fuel, like those you get for free from the Asda/Tesco fuel tanks!
weyland - The octane level has nothing to do with how clean the fuel is. Optimax boasts cleaning additives (which DO work) but the octane level represents the fuels resistance to preignition and nothing else. 97 RON is fine for a 172, and Optimax is better because it is 98.6 RON (on average).
You are correct in saying that performance orientated normally aspirated engines will not really benefit much from higher octane fuels, because thats what they are mapped around - and therefore expect to be run on, but it will suffer big-time on lower octane ones!
I only ever put Optimax in my 172, does seem more lively with a full belly of the stuff, the 95 and 97 ron fuels dont seem to be able to wake the car up...if I go back and put some in the car feels sluggish, or maybe this is all in my mind???
clean16v i know what you mean! i run mine on optimax from day 1! but on a long trip and a bit of gettin lost, i had no choice but to fill at a bp! put in their super unleaded, 97ron i think, and when i put my foot down it felt like it was screamin. altho the next day i kinda felt sluggish again! doh!!!!
I had exactly the same. I put optimax in all of the time, and couldnt find a shell station, and put BP super unleaded in, and I was convinced I was legging it about, rather than just pottering as intended...
i think the fish advert is all a con. It is the government trying to slow everyone down!
Ok you can notice petrol performance with the top speed of your car.... Try a bit of motorway you know well with maybe a slight hill..... then see how fast you can get your car to go!! Your find with optimax your get about 5mph more out of your car on the same bit of road...
Some cars such as the Evo 6 and STI IV even have sensors which detect the composition of the fuel and de-tune (or adjust maps) to cope..... Subaru claim a 15bhp loss is you dont use 98ron (As with the 172s the ECUs primary map is based on using 98ron+)
My experience of fuels (from all round europe) driving a Schnitzer S3, seriously modified RS 500 and a Mk2 172 point towards significant gains when using quality fuels (In europe I found Q8 selling 99ron and on the A30 in surrey theres 1 station selling the aforermentioned!)
Id challenge anyone who thinks the gains are "in yer head!" for me theres no doubt about it! the tone of the engine noticably changes and Im sure Im not the only one to have noticed???
well as i said i used it from day one too, but i keep well on top of my services adn treat my car like a king so if it is only the cleaning properties im not too fussed. just come back from leeds and hit a top speed of 132mph/6400rpm in 5th(95ron unleaded). it took a bloody long time to get there though, i havent seen over 120 with optimax, having said that i have always run out of road. i think you can only claim to have gains if your car is force inducted. my mate swears by it in his g60, but my other mate doesnt notice a difference in his 328i
well after reading all of the above posts, thought I would give optimax a try(also needed petrol!) Usually use Tesco/Esso @ 72.9/litre but thought would bow to the above wisdom so "shelled" out 79.9/litre.
Should I be noticing anything, as cant say I have?!
I read somewhere that the Audi TT 225 gains up to 10bhp running on optimax. Think I read it in EVO last year sometime???? I use Optimax all the time now but have to say I dont notice any difference but for and extra few quid per fill up why not?