Fuel grades... massive climb down & open apology

I must apologies to all for my recent sceptisism and stubborn-ness around the issue of fuel grades - having seen no measurable difference in my Boxster S I was convinced that the increased octane rating offered on forecourts was a marketing scam & waste of money. Having been unable to get more than 280 miles from a tank (around 22mpg) in my 996 (yr 00, 3.4 with 70K miles) I filled up with super (Shell V-Power). Same driving style & journey I was amazed, nay gobsmacked, to have driven 351.4 miles on 55.36 litres!!!!! (around 28.8mpg). To those of you who tried to point out the benefits of super again I apologise for my stubborn ignorance. Why is this difference so notable on the 996 and not on the Boxster??

Not too many gentlemen around. :thumb: Nice to see some more evidence on the topic. Pete

Fantastic, good to hear we're not all mad! And ditto comments above :thumbs:

Quite a few threads on this matter but this is one I started after going round the British Isles in 2007. http://www.911uk.com/viewtopic.php?t=31033&highlight=ron

I get extra mileage from my GT3 (and a BMW 135i) to more than counteract the extra cost. Tested it several times.

Doulas Bader = gentleman ~ Maxie :thumbs:

Fuel Octane The argument has been going on for years. In my personal experience of a VX220, Volvo T5 Turbo and a 996 3.4. The Volvo and Porsche mileage increases by 3 - 4 mpg when using 99 or 98 Ron. It seems to make little difference to the VX220. I understand that this may be because some engines are mapped to take full advantage of high octanes - and some are not. Another factor is how "fresh" all the engine managment sensors are on any given model and their ability to respond to the fractional improvements in the burn quality of performance fuels. On average I have found the miles per pence to be similar between standard and super petrol, so there is no reason not to use super on cost grounds. Super may also improve acceleration if the engine can detect it but I am not going say I could measure in any scientific way - to me it just feels a little more crisp. :?:

Also thought it was a scam - I'll give it a try on my next run down to Brighton! :thumbs:

always use tesco 99 as its around the corner for me. will have to give some of the other brews a try to see if its goes any better / mpg. averages about 18.

It takes someone special to apologise :worship: I've never had to of course.......... Good question - I can think of two possibilities: 1) the Boxster ECU is deliberately 'turned-down' i.e. set to expect no better fuel than 95 RON when it leaves the factory to make the 911 look good - seems very unlikely 2) some ECUs (the Impreza included) have an element of 'learning', or memory. If I put 95 RON in the Impreza, it immediately turns everything 'down'. If I then fill-up with 99 RON, the ECU ignores the new petrol RON it is detecting, and must be re-set before it will turn-up the engine settings. You could do a search to see if the Boxster (being newer?) has a learning ECU? If your alarm system is trustworthy enough to enable you to disconnect the battery on the Boxster, you could fill it up with 99 RON first, then disconnect the battery for 24 hours (which allows any capacitors to drain, so wiping the 'memory') which SHOULD reset the ECU to factory settings, then take it for a drive.

When I bought my Boxster, the OPC salesman said 'I know the manual says try and run 98 RON, just stick ordinary 95 cooking as it makes no difference'.

After an exhaustive internet search, apparently the Boxster might well have a learning / adaptive / memory whatever-you-want-to-call-it ECU. So get filled-up with 99 and then disconnect that battery.

OC, Should the ECU in the 996 automatically recognise the higher RON fuel without the need to disconnect the battery? I only ask because i run my C2 purely on V-power and have done since i bought it a year ago, but the previous owner always put in normal 95 RON fuel. I struggle to get more than 250 miles before the warning light comes - typical daily drive is a 10 mile each way trip to work along a 50mph dual carriageway with a bit of twon traffic mixed in. Sound ok..or should i be getting better? Taran :?:

I'm sorry Taran I don't know - I'm in the 996 forum under false pretenses; I'm fairly sure that the 993 is a reactive ECU - so it looks at the RON of the petrol as it 'arrives', and remembers nothing. I have no idea on the 996, but they might have changed during the evolution anyway. Don't forget the OP saying he saw an immediate difference on a MY00 car suggests it has a reactive ECU?

Hi Taran, It takes about 2-3 washes through of 98 RON for the ECU to recognise the optimal fuel mix. 250 miles sounds about right in your circumstances. The warning light comes on with 50 miles left, so 300 miles out of a tank. I guess your mpg is somewhere around 23-25. Cheers.