Fuel for thought?

Evening all, what with all the Jubilee celebrations and all that I had the fortunate excuse of an anniversary trip to the lake district, some 800 miles in total. Having purchased my 996 C2 in December last year I was looking forward to spending some extended time behind the wheel. Forum consensus was that Shell V power was the way to go fuel wise. Having used V power since purchasing the car I was very happy with the power, delivery smoothness etc. Anyhow a somewhat congested run up the M6 led to a bit more of a spirited drive into Grasmere where I ran into a few porkers, not literally, but all good fun. 400 miles later and time to fill up, couldn't find a Shell garage, so no Vpower, and decided to fill up with BP regular unleaded. On the drive home could not help feeling the engine was more responsive, a bit less grunt between 1500 RPM and 3000 RPM, but pick up was cleaner from lower revs and the engine definitely had more character"¦so heres the rub, does V power give you a smoother more powerful delivery, or does regular unleaded fit in with the designers original brief?

Is your car a tiptronic or a manual?

Hi Rodney, sorry, its a manual...

In order to do a proper comparison, it is best to reset the DME adaption first. As the car is driven, the DME will adapt fuelling and timing values in the fuel map to accommodate fuel quality and driving conditions. If you reset them before a tank of V power, and then before a tank of Regular, you can get a proper comparison. If your car is a MY2000 or later C2, use the attached instructions. If it is MY98 or 99, then you have to disconnect the battery for a minute or two. (But make sure you know the procedure before you try it).

Hi Richard, thanks. Crikey, didn't realise DME even existed, what does it stand for? Mine is a 98, whatever DME is it seems to be working fine. Engine feels very responsive and eager to spin on standard BP fuel. Bst Andy

Hi Richard, Does this DME adaption apply to the Gen II engines as well? I have a Cayman S 3.4 and have always used 95 as a tank of 98 did not change the f.c. at all from the overall average I am getting (31.5). I use it on motorways/ autoroutes where ulitmate performance isn't so important as cost. Would check again on 98 if you think it will make any improvement at steady state speeds. Chris

DME stands for Digitale Motor Elektronik, ie the engine ECU (Electronic Control Module). On a 1998 C2 the procedure for adaption would mean disconnecting the battery for a couple of minutes. If you decide to do that: 1) Make sure you have the radio code, as it will need entering when the battery is reconneced. 2) Switch on the ignition, but don't start the engine. 3) Switch off all the loads you can - Aircon, radio, interior lights, etc. 4) Leave the key in that position, and disconnect the negative terminal of the battery. 5) Wait 2-3 minutes, and reconnect. 6) Switch off the ignition. You will probably find it will make a difference to the performance.

I really don't know. The Gen2 DFI engines use a DME control module made by Continental, so I suspect it may be different to the Bosch Motronic modules used on the earlier models.

OK, but in your experience does 98 offer any improvement over 95 when driving at a steady 70 ish, not wishing to get into a deluge of posts about "whats best for my Porsche is 98 because thats what it's designed for " as so often happens on here.

The car is set up for 98 RON, so if you use 95 then you won't get the same maximum output. The DME will adapt to using 95 by backing off the ignition timing, and I am sure you wouldn't notice a scrap of difference at a constant 70mph, other than the fuel consumption might be slightly less using 98.

Just thought I'd chip in my experience. I've found that I get 2miles more to the gallon over a full tank using 98 vs 95 which makes it ever so slightly more economical than running on 95. it pretty much offsets the extra cost of premium not forgetting any placeabo that may or may not be present

I've only ever put normal RON fuel in mine once when there was no option, and just enough to get somewhere that I could get premium fuel, oh and I drove like an old man and cringed every minute. Perhaps I was being paranoid, but she was designed with high octane fuel in mind as the primary source, it could in reality be fine and I am being a fuss pot, but then this is coming from someone who takes the wheels off and cleans the arches out and the engine if I get caught out in a spot of rain lol!

As expected those" Porsche engines are designed for 98" folks will swear by it and that wasnt my point. Just asked Richard if I could use this DME to properly check it but not on this engine. Just ask your OPC salesman and they will tell you they use 95 in all their demo cars and to fill up new ones for delivery.

My comment wasn't aimed at you, I was just giving my opinion on the topic Each to their own, but I am pretty sure in the technical papers for my Carrera it says not to run for prolonged time with 95 ron, but like I said, I am fussy, and I also don't get the idea of spending a few pennies less on a litre of fuel when already spending out cash on a premium car? Re Sales people that doesn't surprise me at all, they could also just as likely pull hand brake turns in demo cars too when out of site, or thrash them when cold when a customer isn't in it, but that doesn't mean it's ok to do it. Having had experience of detonation in a track car I had once by running low octane fuel I don't fancy going against the manufacturers recommendations. Although the likely hood is, unless you are gunning it around a track at full throttle it could well not make many odds.

Aha, appears I wasn't quite right, less than 95 ron will damage the engine and cause detonation, and must only be used for a short period of time in emergencies and never at full throttle, so that's not an issue in this country

What happens in places such as America where there standard of fuel can he as low as 89 octane?

have a look at this, quite interesting,,, http://en.wikipedia.org/wiki/Shell_V-Power think I will take a trip to Tescos! Bst Andy

Different octane standards are used in the USA. 98 RON=88 MON.

Be careful comparing octane ratings from different countries Chris. Canada, the US and some other countries use the Anti-Knock Index (AKI), rather than our RON, which is 4 to 5 points lower for the same fuel. Check out this link for more info; it makes interesting reading: http://en.wikipedia.org/wiki/Octane_rating Jeff

A good reason to check where your car was delivered, the ECU is programmed differently for different countries because of fuel quality and octane (US has 93 RON if I'm not mistaking). So i.e US cars have a de-tuned engine.

Good point! It seems this has already been answered I know that many models shipped from Europe to the states normally have less output, in the BMW circuit indeed, specifically when I had an E36 M3 and E34 M5 many years ago, the US guys were always in envy of the Euro spec owners. The output and state of tune on those specific blocks in the states were heavily reduced (IIRC something as much as 80hp and as much ft lb) due to emissions and fuelling. However I also know from browsing certain forums that RON ratings are different in the states to the UK. Interestingly though, whilst on this topic, I was quite surprised to hear that as an example the Abarth we just purchased for the wife is supplied in the states with a much higher output and state of tune (the standard US spec is the essesse spec over here). This seemed really odd to me and is against the norm.

[8|]Why buy a performance car and then use an inferior fuel than it was designed for? I tried Shell Optimax in my Audi A4 which has the V6 - 30 Valve engine and found that there was no apparent improvement over the normal shell fuel, but when V-Power was launched I tried that and immediately noticed that the engine was more responsive, smoother and had a slightly improved MPG, thereafter I have only used V-Power. [ ]

Used V power (well ok that's a lie, optimax) and never looked back!