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Turbo cars are different than normally aspirated engines like a 172/182.
The thing is that higher RON fuel is more resistant to exploding as it takes longer before it exploed after being ignited. So turbo cars can stuff more air into the engine ie run more boost when it detects that the engine isnt knocking ie the mixture isnt exploding prematurly and when the fuel is lower RON and it knocks the boost can be reduced till it stops. However normally aspirated engines cannot knock the amount of air back as easily as they would have to close the throttle body.
The new M5 is highly tunned and when that is run on cheap fuel will loose power as the engine will have to reduce air intake volume when the fuel knocks.
Just to complicate matter RON doesnt mean as much as the MON of the fuel as thats higher speed tests. Also RON advertised on the fuel isnt always totally accurate as it is a midpoint number between MON and RON of the fuel.
1
172beast
Evo did a test a while back, got the magazine at work, they took 3 of there long term test cars, all were run on supermarket fuel while they had them. Was a CTR, Jag X Type and a Beemer, M3 IIRC. Anyway, they took photos of the valves before and did some performance testing, mainly in gear times, they then ran on Optimax only for a few months, photographed the valves again and did identical tests. CTR and Jag both had spotless valves afterwards, BMW had no change. Tests showed very little difference but there was a difference, half a second at best on all the tests for the CTR, little difference on the Jag, hardly any on the beemer. Tests could be down to a number of factors though admitably, but the cleaner valves couldnt be down to anything else then the additives in Optimax surely?
But Evo do loads of miles and top gear proved a while back (not that it was necessary) that cars with more miles on them were quicker as the parts had "loosened up".
The aditives will help give a better cleaners burn etc but as for its value well I wouldnt pay the extra personally. Its to difficult to say that just because you spent an extra £100 or whever on optimax during a cars life it performs better as there are to many other factors involved, no two engine are the same.
Sorry if I appeared like that I was having a go at you. I was trying to help people get a better understanding of why turbos are different to normall aspirate cars. And so why the turbo boys sometimes need higer ROn fuel but normaly aspirate drivers (usualy) dont.
Glad I could help though.
1
172beast
Quote: Originally posted by edde on 06 November 2004
Quote: Originally posted by 172beast on 06 November 2004Was a CTR, Jag X Type and a Beemer, M3 IIRC. Anyway, they took photos of the valves before and did some performance testing, mainly in gear times, they then ran on Optimax only for a few months, photographed the valves again and did identical tests. CTR and Jag both had spotless valves afterwards, BMW had no change. Tests showed very little difference but there was a difference, half a second at best on all the tests for the CTR, little difference on the Jag, hardly any on the beemer. Tests could be down to a number of factors though admitably, but the cleaner valves couldnt be down to anything else then the additives in Optimax surely?[/QUOTE]But Evo do loads of miles and top gear proved a while back (not that it was necessary) that cars with more miles on them were quicker as the parts had "loosened up".The aditives will help give a better cleaners burn etc but as for its value well I wouldnt pay the extra personally. Its to difficult to say that just because you spent an extra £100 or whever on optimax during a cars life it performs better as there are to many other factors involved, no two engine are the same.
Very true but valves dont clean themselves as they get older, theyll get more clogged up, I aint saying it makes your car quicker cos Ive ran my 172 on both for some time and never noticed a difference, but the cleaning additives must work. Whether thats worth the extra cash or not is anyones guess lol we all drive Renaults, theyll fall apart by the time Optimax does any difference to our engines anyway
Renault Laguna Coupe
I buy 98 for trackdays etc, dont bother the rest of the time to be honest.
As an example, lets say the 182 does 35mpg average. I find mine does better than that and I drive in mostly urban conditions so if anything I am over estimating the amount of fuel used.
So taking 35mpg and the price difference between Shell 95 RON and Shell Optimax calculate how much more Optimax would cost based on 150,200 and 250 miles per week.
Then you will see why I only ever use Optimax and never worry about the cost.
Renault Clio 172 Ph2
it will take a few tanks of fuel to give you the blessings of higher ron fuel. teh 172 is setup to use high ron anyway.
Elise/VX220/R26
Ive done 1/4 miling in near identical conditions, once on optimax and then on 95 ron, got exactly the same times. Im under no illusion that the car feels different with it in. As a matter of fact I put some optimax in today by accident (drove up to pump where they were out of 95 ron) so I thought Id go for a drive just to see if the car had "the extra power needed to respond more quickly"
did it chuff, its just the same. You can say it over and over again but some people think that just because its more expensive that its better for you car. People like to "treat" their cars, thats fair enough but IMO the extra cash would be better spent on an air freshner or something.
As for octane booster LOL is all I can say. If you look at the smallprint youll see that it doesnt boost the octane value of your fuel at all. It supposedly cleanes your fuel system, making the most of the actual fuel youve put in. Dont think my 2 year old car would really benefit from a fuel system clean with 20k on the clock.
Bottom line is that theres a lot of bullsh*t in the automotive trade, just dont be a sucker for it.
Shiny red R32
There was a fuel survey a few months ago and the conclusion was that OPTIMAX IS A RIP-OFF and has no benefit to anyones car, only to the fuel companys profits- any improved performance is all in the mind!
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Monday 8th March 2004
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Optimax Fuels A Watchdog Blast
Shell has been rapped for making claims about its Optimax petrol that ex-perts say arent true.
The company said in leaflets that its product "gives you an extra burst of fuel when you need it", but the Advertising Standards Agency ruled this would not apply to all cars. The judgement also said Optimax may not be "the best performance unleaded", as claimed by Shell.
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Remapped derv Golf
98 RON is standard unleaded in France isnt it? Didnt think they sold 95 in most european countries
your meant to use super unleaded or optimax in ya 172/182 anyway. inside the filler flap theres a sticker telling u.
optimax definately works better on my bike but in my last car it was no different. im sure the clio will run better with it cos its designed to run on it. they know what theyre talking about these engine bods
Edde - the RON level of the fuel can affect when you can time the ignition of the fuel/air mixture, and thus change the power output of the explosion....
In my example my 172 was tuned for 98RON fuel, and you can tell the different if you go down onto ordinary unleaded fuels..... no doubt, and although I know you can run any 172 on 95RON unleaded the ecu is actually changing the timing to account for the reduction (retarding the ignition I believe?) and the are setup for the higher level RON, but can cope with the lower levels more commonly available.
In my view higher RON fuel is wasted on the stock engine whatever the amount it cleanes the valves etc.
You cannot make more power though on 98 RON rarther than 95 RON unless your talking about the engine knocking though and so intake air etc being reduced.
Anyway if the cars reducing its timming for the lower RON fuel it isnt necessarily making less power just the fuel takes less time to go through its preignition so the timing has to be changed so that the pressue rise is maximised over a particular crank angle.
What were the T/B mapped for? 98 RON?
Im interested to learn if Im wrong but Im not convinced that Im wrong (famous last words).
Clio 197
IMO, if a car is designed to run on 98, then it will run "better" on 98...
...BUT, how much better?
Its a bit like two identical cars, one with a full winscreen washer, and one with an empty winscreen washer... one weighs 5kg more, but in reality how much of a difference is it going to really make?
Car manufacturers quote which fuel they use to get the bhp/economy figures etc, because it does make a difference, but Im not convinced its a big one!
