st4
Banned
suposedly better MPG and higher performance. I think it helps with cleaning the engine and deposit build up. I ran a BMW I6 on super and it was better with super than normal fuel, much more refined.
A high compression engine works well with super unleaded. Compression ratios of less than 9.5:1 are fine with normal unleaded.
A high compression engine works well with super unleaded. Compression ratios of less than 9.5:1 are fine with normal unleaded.
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I mostly ran my Impreza Turbos on Optimax, they ran much smoother than on regular unleaded. Don't really know if it improved performance, but they just seemed to prefer it. My C43 was either run on Optimax or Tesco 99RON, never ran it on regular so nothing to compare it to. But you don't buy an AMG if running costs are your primary concern. 
Now I'm stuck in the Golf, it gets whatever's cheapest. And my old Fiat runs on anything so long as it's vaguely combustible.. probably a 50/50 mix of diesel and tapwater would do..
Cheers,
Gaz
Now I'm stuck in the Golf, it gets whatever's cheapest. And my old Fiat runs on anything so long as it's vaguely combustible.. probably a 50/50 mix of diesel and tapwater would do..
Cheers,
Gaz
Super unleaded has a higher octane number than Normal Unleaded. This basically means the due to its higher octane number it is more resistant to "detonation" which takes place within the engine whenever you depress your accelerator. I've heard that this benefits performance/forced induction engines (basically engines which have more than the average stress on it).
The reasoning behind it is that when you ask for power, the more resistant to detonation the fuel is, the less unburnt fuel you will waste if you happen to lift off your foot from the accelerator very quickly. In Naturally aspirated cars that aren't built for performance in anyway (a completely unstressed engine) this isn't required, as they usually have a lower compression ratio within the cylinders than when compared with an engine built for performance, or has a forced induction structure to it.
You can refer to the manual of the car in question, the manfacturer's will always recommend what fuel to use.
I read this somewhere on a chemistry blog though, i could be a bit out.
The reasoning behind it is that when you ask for power, the more resistant to detonation the fuel is, the less unburnt fuel you will waste if you happen to lift off your foot from the accelerator very quickly. In Naturally aspirated cars that aren't built for performance in anyway (a completely unstressed engine) this isn't required, as they usually have a lower compression ratio within the cylinders than when compared with an engine built for performance, or has a forced induction structure to it.
You can refer to the manual of the car in question, the manfacturer's will always recommend what fuel to use.
I read this somewhere on a chemistry blog though, i could be a bit out.
Dieselman
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Sure is.
A higher octane petrol is more resistant to detonation, but no engine should be detonating the fuel mix, it can destroy the engine in short measure.
Detonation or Pinking is a term used to describe pre-ignition detonation, or compression induced detonation as opposed to spark induced.
Charged cars ar more susceptible due to effectively raising the compression ratio due to the air being at higher than atmospheric pressure.
As far as wasting more or less fuel with a higher octane petrol, that's incorrect. What is meant is that due to the mixture burning more slowly it applies pressure down onto the piston for longer so more power is produced, thus less petrol is consumed.
Only cars with automatically advancing ignition timing will benefit from a higher octane fuel, assuming they can tollerate lower octane due to lower compression ratios.
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Dieselman
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It shouldn't be.
Detonation is uncontrolled burning, whereas the fuel should have rapid burn due to a spark being applied.
Detonation is uncontrolled burning, whereas the fuel should have rapid burn due to a spark being applied.
st4
Banned
I was given a rule of thumb that the octane rating related to the minimum grade you should use in you car.
eg. 9.5:1 compression ratio means you should use 95 octane fuel.
10:1 compression means a fuel of 100 octane should be used.
Don't know if its an old wives tale or not.
eg. 9.5:1 compression ratio means you should use 95 octane fuel.
10:1 compression means a fuel of 100 octane should be used.
Don't know if its an old wives tale or not.
R129mine
Active Member
i recently asked at the BP service station if anyone paid 244p (this was 3 weeks ago) for a litre of their high performance fuel i think they call it BP ultimate and she said yes quite a few people do, i think paying 5p extra for high performance fuel is do-able but 244p per litre!
jonm
Active Member
A couple of months ago I accidently filled up with the 'super stuff', nearly had a heart attack when I noticed what I was doing. Resulted in one of those john Cleese--eske moments when you look at you hand, relise what you are doing and pull it away sharply hoping everything will be O/K..anyway.
As an experiment I watched the MPG thingy for a while and I was definately getting more, around 3 mpg, which dropped back down when back to the 'old' stuff.
So, in conclusion (from 1 tankfull) I can get nearly 10% more mpg by paying more than 10% extra for fuel...not worth it.
Jon
If the car isn't pinking, You will not see any benefit from running superunleaded. If you have advanced the ignition and/or upped the boost (run performance chips) then it will stop this pre-detonation occurring.
I run regular unleaded in my bike which running 10.5:1 compression and is making 115bhp on the crank out of 600cc @ 14,000 rpm and never had a problem with it.
I run regular unleaded in my bike which running 10.5:1 compression and is making 115bhp on the crank out of 600cc @ 14,000 rpm and never had a problem with it.
Not necessarily true.
My car doesn't pink on 95, it also doesn't pink on 98, 99, any other fuels i've run 3 or 4 tanks through in one go.
I have to map our gas engines at work, it makes 11,500hp and if I advance the timing I will get more power. You can see it straight away by a reduction in throttle needed for that load.
Now, if we see that in a car, especially a car that alters the timing to suit the engines condition then you will increase the mileage AND increase the performance in one fail swoop.
The Octane rating (Like dieselman explained) is basically the fuels resistance to detonation, which means it's harder to ignite, so will only ignite exactly when the engine tells it to.
If you can feel the performance gains is one thing, but mileage gains, especially on real time reading gauges are obvious to see.
My bike (1995 Carb ZXR750) is noticeably more responsive when I use V-Power compard to regular unleaded, I've not noticed any mileage gain though, but this is hard to see on a bike and in theory anyway, it shouldn't change.
In the Merc, I don't feel any performance benefit (It is a lowly 65hp/ litre mind you) but I do feel a benefit in economy and hot idle quality.
On Tesco 99 I get roughly 10% less economy, 500km instead of 550. My friends M5 reacts the same.
To me the benefits are worth it, I use it in all the cars I drive when I have to fill up with fuel and will continue to do so. How much of this is down to Placebo though, is very hard to establish.
Aslong as you are happy, then pop any petrol in at all.
Dave!
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Dieselman
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Your description is bang on and contains vital information. Only vehicles that automatically advance the timing to the point of pinking will have gains running on higher octane fuels.
The ECU advances the timing until detonation is just started then retards it slightly.
An engine where the timing is fixed Will not noticeably benefit from a higher octane fuel.
Does the 500E use a knock sensor to set the timing or is it fixed.?
Kompressor_Dude
Active Member
Do many of the mercs use advanced timing. W202 for example? I always put the good stuff in mine and it does seem to improve things, however this may just be my mind justifying the extra money i spend!
Cheers
Cheers
st4
Banned
My old BMW did and thats why it ran better on 97 than on 95.
http://en.wikipedia.org/wiki/Compression_ratio
I genuinely don't know if the timing is altered through a knock sensor or if it's altered through the Lambda readings.
I know on some older cars the knock sensor detected knock and then would do a derate by removing say a couple of degrees of advance. Modern systems probably alter this on each cylinder though.
Either way the benefits are there to be had if your engine allows it.
Dave!
would my E230 96P 210 estate have such an engine?
Do many of the mercs use advanced timing. W202 for example? I always put the good stuff in mine and it does seem to improve things, however this may just be my mind justifying the extra money i spend!
Cheers
Our cars recommend super on the inside of the fuel cap thing, so there's must be a reason for it.
