Another fuel thread... - The Unofficial BMW M5 Messageboard (m5board.com)

illjah · 16th November 2005, 13:34

I know this was covered recently, and I stated that for me "petrol is petrol" and the cheaper the better with the miles I drive.

BUT the petrol seemed to have droped about 3p a litre around here - so standard unleaded around 90.9-91.9. Well I had a Tesco 5p off a litre token, and they had 99RON at 95.9, which seemed pretty reasonable (90.9 with my token) so I thought I might give the 99RON a go, and was well sceptical - convinced I would feel no difference.

But as soon as I started it I noticed quite a big difference - it started easier and smoother, and lower rpm is soo much smoother now. Also feels smoother from a cold start today as well. Can't notice any performance difference at all. Also I notice no difference over 4000rpm.

The big difference may be as I have a non-OEM chip in now that may perhaps be expecting higher RON, but I was very, very surprised!

hertfordshire1 · 16th November 2005, 14:40

Alan,

I know what you mean. When i run my car on the 99 RON it does seem to idle smoother..

However, it was stated that these cars were developed around 95 RON, so thats all mine sees these days.

Steve

Jahangeer · 16th November 2005, 15:16

I've been told to run mine on 98 by the tuner who installed the UNICHIP.

unesential · 16th November 2005, 15:36

I believe once chipped it is advisable to run higher octane to avoid detonation caused by the timing change inherent in the chip.

illjah · 16th November 2005, 15:45

Quote:

Originally Posted by hertfordshire1

Alan,

I know what you mean. When i run my car on the 99 RON it does seem to idle smoother..

However, it was stated that these cars were developed around 95 RON, so thats all mine sees these days.

Steve

Yes agreed - but now mine has an aftermarket chip, I'm thinking it may be better for me to use higher RON - but if it doesn't return extra efficiency I don't know if i can really justify the extra cost.

illjah · 16th November 2005, 15:47

Quote:

Originally Posted by unesential

I believe once chipped it is advisable to run higher octane to avoid detonation caused by the timing change inherent in the chip.

I'm thinking this too - wished I'd tried higher RON fuel before the chip to see if the difference is the same - I need to find out whether the chip I have is designed for 98RON+ and whether running on 95RON is going to cause me problems.

Rob Plummer · 16th November 2005, 16:03

Quote:

Originally Posted by illjah

Yes agreed - but now mine has an aftermarket chip, I'm thinking it may be better for me to use higher RON - but if it doesn't return extra efficiency I don't know if i can really justify the extra cost.

Extra cost is covered by increased MPG - see my thread on a similar subject.

unesential · 16th November 2005, 16:11

Quote:

Originally Posted by illjah

Yes agreed - but now mine has an aftermarket chip, I'm thinking it may be better for me to use higher RON - but if it doesn't return extra efficiency I don't know if i can really justify the extra cost.

Cost of engine rebuild do to damge from detonation far offsets any difference in MPG, why take the chance.

illjah · 16th November 2005, 16:12

Quote:

Originally Posted by Rob Plummer

Extra cost is covered by increased MPG - see my thread on a similar subject.

Yes I saw that thread - it was that thread (and my 5p off a litre token - thanks to Jon Baker in that thread as well!) that made me try the 99RON. But I need to see that improvement for myself - I'll find out very soon.

Rob Plummer · 16th November 2005, 16:14

Quote:

Originally Posted by illjah

Yes I saw that thread - it was that thread (and my 5p off a litre token - thanks to Jon Baker in that thread as well!) that made me try the 99RON. But I need to see that improvement for myself - I'll find out very soon.

Yeah - but if the real cost ISN'T any higher, thanks to the better MPG, then why NOT use it?