knobby_2000

Hi Guys

I have a trip planned to the highlands of Scotland in the very near future and will be taking the Impreza...
She is a UK model so I guess she is capable of running fine on standard 95ron fuel...all be it with a little less power...

I have never ran the car on anything other than Tesco99 or Shell VPower....and feel a small pang of worry when I consider changing fuel grades...the last time I took her up north it cost a small fortune on the full grade, would have been cheaper to fly!!!! But this time I was thinking would it be ok to run the car with 95ron just for the trip and running around up there just to save on the pennies, then refill with the full grade once back home?....

Would I need to reset the ecu to make the car feel more at home on the lower grade or fill with a 50/50 split (95/99ron) and let her get used to it a couple of days before going?.... or am I just being way too over sensitive .....(hey I cant help it I love her to bits )

borat52

If its a UK with a standard map then unless it says 'super unleaded only' (I seem to recall the P1 and 22b having this warning, but I may even be dreaming on that) then theres never any need to put anything other than 95ron in. UK's were mapped for 95 RON, 99RON is a waste of money as it will not be mapped to take advantage of the extra resistance to det that the 99 offers and just assumes its always getting at best case 95 ron.

You could have a forged 2.5 with a massive turbo, and if it was mapped for 95RON then there would be no need to put 99RON in.

Super is not 'better' for you engine per se, it does however offer greater resistance to det which means you can map more aggressively if you know that super is all that will go into the car.

TonyBurns

iTrader: (3)

99 isnt a waste of money, these cars actually run better on a higher octane fuel, 95 is the minimum spec fuel you can use, running on a higher octane will increase performance slightly and also increase your mpg

Tony

knobby_2000

So changing to 95ron for a long haul run for a couple of weeks won't make a lot of difference...well perhaps only in the wallet dept?

Cheers guys.

borat52

Really? I have a pre 1996 myself and I'm fairly sure the ECU cannot adjust timing to take advantage of better fuel, so it really is pointless putting anything more than 95ron in a stock pre 1996 UK turbo. Are the latter ECU's able to do this?

knobby_2000

Im not sure about the ecu on the 97> models....but through personal experience Vpower gives the car a better pickup and what feels like a crisp feel to the car at lower speeds compared to Tesco99...obviously higher speeds feel pretty much the same no matter what fuel...having never used 95ron in the Impreza I cant compare the fuel but in my BMW Vpower rules over 95ron everytime if just for the sharper response.

hrness

my my01 although in book it says 95 the ecu will adjust for higher, according to power engineering the ecu can either be reset or run a few tankfulls through, made a big difference to how mine ran. now use tesco99 get better mpg and it def runs sweeter even sounds better, 95 is ok on a uk model but timing will be pulled in. and advised if using 95 dont cane it

Dee NI

Interesting, as the sticker on the fuel cap on my 99uk says 95ron. I ran with super a few times but never noticed anything. I can't see how if it's meant to be run on 95 and you run it on 95 that caning it would do it much harm..
Maybe I might have noticed a difference if I reset my ecu but then that would be a pain in the **** to do unless I was going to use it all the time.
Hoow bout using proboost or them additives? They any use along with 95 in making it a bit 'stronger'


Damien

Skooby53

iTrader: (1)

I ran my MY99 impreza on 95 RON for 5yrs as I was told by Subaru that the UK spec car will be tuned for this fuel. I have, for the last 2yrs ran it on Super Unleaded and it is without doubt much smoother and picks up much better than it did on normal unleaded.

So, unlike many I have owned the same car for 7 yrs(Can't bear to part with it!) and can honestly say unleaded will be fine and super unleaded will be better, if available at a reasonable price. If you are still worried then just listen to 'hrness' and don't cane it!

weeebell

iTrader: (1)

When you think of it, how much of a difference is there between a tank or 95 and a tank of 99? 1ltr per tank?
I allways use tesco 99 and 3 weeks ago is was 96.9p, now its 100.9p and I dont even get 1ltr less than I used to.

borat52

I'm not sure what ability the ECU has on >96 cars to adjust for higher octane fuels but I dont buy into 'the cars more responsive on super' for a UK turbo. The reason being all the octane rating means is the fuels resistance to detonation, in the states they even refer to the octane number as the Anti Knock Index (AKI). This means the only property of 99 octane over 95 octane is that its more resistant to detonation. For a car mapped for 95 octane fuel the ECU will run on 99 octane excatly the same as on 95 octane, the spark will occur at exactly the same point and as long as the calorific content of the fuel is the same (tesco 99 is actually less due to its ethanol component which is why the fuel economy can be marginally worse) then all aspects of the 99RON and 95RON burning in the engine will be identical. It is impossible for the 99RON to make the engine 'more responsive' unless is can alter the ignition timings of its own accord or the car was mapped for 99RON.
I'm an open mind though, if someone can point out one reason why 99RON would make a car mapped for 95RON more powerfull/efficient/responsive then I'll hold my hands up and say I was wrong.



There has been a recent test on super in some mainstream magazine/publication stating pretty much this but I cant recall it off hand.

Heres a reasonably good explanation on octane:

Epinions.com - Premium vs. Regular Gas: How to Decide

Its also the same story with supermarket fuels, it was all the rage at one time to suggest supermarket fuels were terrible and would damage your engine. The reason being they were a few pence cheaper. In reality they came from the same refineries as the likes of BP. Why were they cheaper? Simple supermarkets have cheap space, cheap staff on tap and best of all a customer throughput that most BP stations would kill for, so they could reduce their take on each litre by a penny or two by knocking down their overheads/litre compared to independant stations. They sold more litres with less overall costs than their competitors, the fuel was/is technically the same.


Note, its a different story with imports, fuel in japan has been 100RON for some time, running 95RON in an import is likely to cause detonation/blown engine.