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So, reading the handbook on my new 55, it tells me to fill up with 98 RON

Researching the various 'big name brands' here in the UK I find that:

BP Ultimate : 97 RON
Total Excellium : 97 RON
Esso Energy : 97 RON
Texaco Super : 97 RON
Shell V-Power : 99 RON

Not sure about the supermarket chains, but feel I should be putting in the juice from a main player..

So what's a guy to do?, there is no 98 RON, will the 97 do the job, or should I go over 98 for the V-Power 99..?
 

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I only have the 350 but I run it on supermarket plain unleaded. Personally I think 99 would be a waste of money. I cant see 97 doing any harm
 

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After 6 years with an S2000 needing SUL, my personal choice for best performance and running would be either Shell V Power or Tesco Momentum 99. That's also what I'm currently using in my R172 SLK55 too, but haven't had a chance to give it some beans yet due to the crap weather.

Would really steer clear of BP, the S2000 ran very poorly on their 97 RON stuff.

My motto is always best fuel and best oil you can afford, athletes don't eat rubbish do they?

RR
 

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My motto is always best fuel and best oil you can afford, athletes don't eat rubbish do they?
Agreed, after spending so much on the car, i'm not trying to save a few pennies on each tankful :)

It's just sooo confusing with them all being 'super unleaded', and ranging from 97 - 99 RON.. lol

I suppose if the handbook says 98, and we assume that they mean this is the minimum grade required, it can only really be V-Power or Tesco's Momentum, that I need to stick in it..

The reason for the question is that, I went to a specific garage on Saturday to fill up (Esso), as I was going to Maidstone shopping anyway, and then when I got there and saw it was only 97, I only put a tenner in, and drove away in disgust... lol
 

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Hi Swagman

After the last post on this subject i have revisited the super-unleaded(Tesco) pump this last fill up , Only 3/4 of a tank to full so im keeping with s/unleaded for the next 2-3 tank fulls & see if it improves the way the car runs .

Cheers

Andy
 

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Hi performance engines normally have automatic knock detection so lower RON fuel, even 95 won't do any damage for a couple of tank fills if SUL isn't available however I wouldn't like to run a high performance car for an extended period on low octane fuel.

I think the difference between 97 and 98 isn't too great, however most people I know who run high performance cars use V power and momentum, perhaps because they have the highest octane rating.
 

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Its never good to run on lower octane for your car for a long period. Anything above and the car will love you for it.

But if you happen to get caught out and no high octane fuel around, fill up a tenner's or so worth with either normal 95 or 97 and drive to a station with the high octane stuff.....no WOT!

TBH, felt no significant difference between V-Power and Momemtum 99. Just like to use VP more for its cleaning agents.
 

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Hi performance engines normally have automatic knock detection so lower RON fuel, even 95 won't do any damage for a couple of tank fills if SUL isn't available however I wouldn't like to run a high performance car for an extended period on low octane fuel.

I think the difference between 97 and 98 isn't too great, however most people I know who run high performance cars use V power and momentum, perhaps because they have the highest octane rating.
Almost all gasoline engines today, not just 'high perfrormance' have knock sensors and the ability to retard the ignition timing in response to knock. Using 95 RON in an engine calibrated for say 97 RON is not a particularly smart way of running the engine.

a) Relying on a 50 pence sensor to protect a £5k engine to save a couple of quid at the pump is a bit of flawed logic to me.

b) Running with retarded ignition timing reduces engine efficiency resulting in higher fuel consumption (less miles per gallon) and less power and acceleration. So the saving made at the pump is lost in any case.

Some engines actually benefit from higher octane than they were calibrated for, certainly worth trying a tank or two of 'the good stuff' before discounting the potential benefits. This is not easy to explain, so I'll not try.

Finally some premium fuels ;) have more cleaning additives than others. I prefer clean inlet valves and injectors to dirty ones...
 

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ron number to octane number

just a little info.

Some foreign vehicle manuals recommend a Research Octane Number (RON) instead of the more common octane rating that appears on most gasoline pumps. As a rule, the recommended octane rating can be determined by subtracting four (4) from the recommended RON number. A vehicle that calls for "91 RON" should use 87 octane gasoline (as measured by the (R + M) / 2 method). Using a higher grade than is required will not usually increase performance. However, if the vehicle is equipped with knock sensors, as many late model vehicles are, a higher octane grade may enhance performance.

woot i like that last sentence:rb
 

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just a little info.

Some foreign vehicle manuals recommend a Research Octane Number (RON) instead of the more common octane rating that appears on most gasoline pumps. As a rule, the recommended octane rating can be determined by subtracting four (4) from the recommended RON number. A vehicle that calls for "91 RON" should use 87 octane gasoline (as measured by the (R + M) / 2 method). Using a higher grade than is required will not usually increase performance. However, if the vehicle is equipped with knock sensors, as many late model vehicles are, a higher octane grade may enhance performance.

woot i like that last sentence:rb
As your in Canada and I'm in the UK, the SLK is a foreign car to both of us...

USA and Canada use (RON+MON)/2 to define the anti-knock index or AKI. The difference between RON (Research Octane Number), and MON (Motor Octane Number) can vary from blend to blend and is called sensitivity.


The AKI approach may be thought of as a better descriptor of octane quality, but it's by no means universal. Outside of the USA and Canada, I think the rest of the world uses RON as the headline figure at the pump.

In Europe, EN:228 proposes a minumum of 95 for RON and 85 for MON. So a sensitivity of 10 octane numbers might be expected, but real fuels can be different and still meet the regs. For example, sometimes the refinery has to 'give away' octane in order to comply with other properties defined in the specification.

If you fancy a more detailed read about octane, have a butchers at this:

http://www.crcao.com/reports/recentstudies2012/CM-137-11-1b Task 2-5/CM-137-11-1b Final Report.pdf

As for 'knock sensor equipped engines may give more performance'. Strictly speaking, if the engine were perfectly calibrated there would be no benefit on running it on fuel with higher otctane quality than the calibration fuel. The knock sensor only provides a signal when the engine knocks on fuel that has insufficient octane quality to prevent knock.

In practice, some engine calibrations have some headroom and therefore the engine is able to benefit from higher octane fuel. This isn't due to the knock sensor.

Just trying to provide some clarification BTW.
 

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Hi All petrol heads

Well on to my 2rd tank of super unleaded 97 ron , I think there is a difference but as i drive a smart fortwo all week it may be just that , The wife keeps asking if im in sport mode LOL . I may try some V power 99 ron next fill up .


Cheers

Andy
 
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