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Super unleaded

dereksharpuk

dereksharpuk

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Has anyone noticed that the 997S really does need super unleaded petrol. My 996 ran fine on ordinary, but my 997S does not like it. OK, so the book says super unleaded, but it said the same for the 996
 
I read I believe on this forum that Tescos of all places is selling 99 RON at selected outlets. Had the chance to fill up a very empty tank last week after some brinkmanship traveling south on the A34. Can report very smooth power delivery across the rev band, particularly noticeable at wide throttle openings from low RPM. For the record normal juice Optiplex. I agree 997S does not appreciate normal unleaded or the cheap French stuff.
 
I have found the car runs best on Shell 98 RON and is about 1mpg better compared to running 95 RON. The difference is most noticeable in throttle response - a bit like the difference in throttle between normal and sport for sport crono spec'd cars.
 
I have used 95 Ron all the time (9,000 miles now) a part from a track day, I do notice some pinking at the lower end, but I chug around most of the day, so no real performace issues for me.
 
I belive the 996 had a compression ratio of 11.3:1 as does the 997 Carrera but the 997 Carrera S runs a compresion ratio of 11.8:1. Would this account for apparent liking of higher Octane fuel?
 
I have now tried a few tankfuls of the Tesco 99 ron. To be honest, I don't notice any real performance or economy difference over Shell Optimax, although it is 3p or 4p cheaper per litre.

Every little helps! [:D][:D]
 
Interesting ! I met with the Global technical manager for BP fuels recently (incidentally he may well be coming to the September MK / Northants meeting to talk about fuels) and took him to task w.r.t the Tesco 99RON fuel.

This is what he had to say.

Steve - I can only comment on what facts I know, but yes I believe there is a Tesco product at 99RON which achieves some of this higher octane through the use of ethanol in the blend - this has limited availability. Ethanol is allowed in fuel up to 5% according to EU legislation. OEMs do not recommend it's use in Europe at greater than 5% content (ref ACEA Worldwide fuel charter). In the US ethanol can be found at up to 10% in gasoline and of course in Brazil 22% ethanol in gasoline is common place.

Being an oxygenate, ethanol based blends in general will disturb the air fuel ratio setting of older vehicles without a closed loop AFR control, and in addition there will be a small increase in fuel consumption due to the lower calorific value, but the key issue is to ensure that the vehicle fuel system is compatible with use of ethanol based blends. Typically common questions which arise are:

Corrosion resistance of fuel system to ethanol
Seal compatibility with ethanol blends
Water uptake with ethanol (Although at the 5% and less level there is no clear evidence of problems.)

Rgds

Craig
Click to expand...
But he could be wrong of course.
 
Yes - already discussed this with him

The BP fuel (like Optimax) takes a regular 95 octane fuel and blends a proprietory additive. Yes..."Optimax" is Shell + "X". X being someone else's magic fairy dust.

BP use the same fairy, but slightly different parameters with a friction modifier.

Anyhow, the RON value is Research Octane Number, but he is suggesting (and I agree) that MON is as / more critical, but almost never quoted in the UK. For some reason (I'm as guilty) we have all been focused on a polarised view of RON as the value of fuel "quality" - so 99 must be better than 98 etc..

In fact, the MON is more valid under real world conditions.

If you need to know more about RON vs. MON then click here

I'm sure we all have plenty more questions for BP / Shell when it comes to petrol and perhaps when he comes to the club meeting in september, we'll have some answers.
 
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