95 or 98 RON?

[spiker]

Thanks for clarifying Kristian

 

[flat6]

There are now 2 threads running here. The original was 95RON vs 98RON (regardless of where you buy it) for which your car's knock sensors will detect the difference and retard the ignition. For this reason, I use high octane fuel (Tesco 99, Shell VPower and BP have different RON ratings but i'll call them high octane) The second thread is supermarket fuel vs Shell/BP etc. (regardless of the RON). In answer to this question. I will use supermarket fuel but I feel the additives of other brands who specialise in this stuff, can only do some good so I tend to use them more. I did feel that my car ran better when brimmed from empty on V Power than when I brimmed it from empty on Tesco 99 but I have no scientific evidence, so won't offer that as fact (don't know if it was the additives or something else about the fuel or my imagination). However, I tend to use V Power mainly and mix with Tesco 99. I haven't seen high octane fuel at my local Esso.

 

[Alan_Armstrong]

I have always used 98 ron fuel in my Cayman S since new, originally there was something about the variation from a Boxster engine that called for 98 over 95 ron...I cant remember what it was..... No doubt some of the discussion is over cost between the 2 ron levels.... Since I now have a deisel car for day use, and regularly have to £1.40 - £1.42 per litre, it no longer comes as a shock to pay for the 98 ron fuel in my Porker...which runs at a simular price!

 

[tscaptain]

From the 2010 (US) Cayman owners manual Your engine is designed to provide optimum performance and fuel economy using unleaded premium fuel with an octane rating of 98 RON (93 CLC or AKI). Porsche therefore recommends the use of these fuels in your vehicle. Porsche also recognizes that these fuels may not always be available. Be assured that your vehicle will operate properly on unleaded premium fuels with octane numbers of at least 95 RON (90 CLC or AKI), since the engine’s “Electronic Oktane™ knock control” will adapt the ignition timing, if necessary. Sparkling wine or champagne - I know which I prefer[]

 

[chrisH]

As I said earlier this comes down to a personal decision rather than anything else and I predicted there would be a deluge of posts from those who feel they are feeding their Porsche to the best possible diet of 98 rather than 95, both meet the design spec as the Captain shows. I have tried a tank full of 98 and it made zero difference to my overall mpg of 31.7.

 

[Motorhead]

I'm sure that you're right Chris. I try to use V-Power when available but I'm not paranoid about it - and the Shell Club Card vouchers help to offset the additional cost somewhat. Incidentally, in a previous post I mentioned that the ethanol content of 95 octane fuel is likely to increase from 5% to 10% in the near future (although Shell have indicated that the ethanol content of V-Power will remain below 5%) and that this may have an adverse effect upon both performance and fuel economy. Here are some relevant volumetric energy density figures (units are Watt-Hours/Litre): Diesel 10,942 Wh/l Gasoline 9,700 Wh/l Ethanol 6,100 Wh/l So, using 95 rather than 98 octane fuel may be better for the planet but is likely to downgrade your performance and economy . An ethanol-diesel Cayman maybe..!! Jeff