BoroWRX

Someone please enlighten me , my first WRX , does it matter if I use Optimax , BP or Tesco Supreme as long as its 97 ron or up , the price difference with these guzzlers makes a difference as Tesco is nearly 10p cheaper .....

ALi-B

iTrader: (1)

Which WRX you talking about?...

newage UK/euro Or a jap import/classic shape??

One needs it, the other doesn't

girl-in-a-scoob

In My honest opinion... The Tesco 99ron makes my04 wrx juddery in the mornings... other people havnt found a problem with it.... It's something to do with ethanol...

Claire

BoroWRX

I have a 2002 WRX BugEye UK Spec , I have found it a little juddery at times but I think thats with any fuel ? since I got the car two months ago it doesnt seem to rip my face off quite like it did at first , but maybe I got used to it , I have changed the filter to KN and the brakes but nowt else ....
will be at show on sunday by the way

ALi-B

iTrader: (1)

It's only the old Jap import WRX that "must" use Super (well, they "should" use 100RON). Stick in whatever makes you happy on the Uk ones (except diesel )

BoroWRX

under the fuel flap it states Super Unleaded Fuel Only ?

ALi-B

iTrader: (1)

It also says gasoline

The manual is more accurate for descirbing which minimum RON fuel you can use. Unless you had a PPP fitted which does need super UL.

Daz1121

I've got a MY00 UK Turbo 2000 which I tend to run on Optimax. Only mod's are a Magnex system 1st cat back and rear de-cat. Have used normal unleaded for a while with no problems but prefer to use what Subaru have designed the car to run on.

COLZO

You can actually run them on normal unleaded but I would recommend Optimax or BP Ulimate. I have a 05 STI PPP and Prodrive advise you to use 97 ron or above. Whatever you feel gives the best performance/MPG stick with it.

AVI-8

This subjects been done to the death

On 5th gear a while ago they did a test on fuels to see if there was a benefit of using higher octane fuels.

They used three cars, a girlie supermini, a family saloon and quess what, an Impreza turbo.

They tested three fuels in each car on a rolling road,

Normal supermarket unleaded
BP Ultimate
Shell optimax

Between tests the ECU;s were reset, on the first two cars there was little difference between the fuels

But with the Subaru there was a noticable difference, I cant remember the exact figures but it was somewhere in the region of 15 bhp more with BP ultimate and 18 with Shell optimax.

The reason it made such a difference on a turbocharged car and not the other two cars is because the higher octane rating allowed the engine to produce more boost.

My car has a PPP and I always use optimax whenever possible and the car definately feels a bit more responsive with it.

Although theres many people on this site will tell you that theres no difference

The Rig

iTrader: (13)

subaru designed the uk spec to use 97 ron, not optimax as when the cars were released,optimax wasnt around.

ALi-B

iTrader: (1)

Hactually, it wasn't designed for a specific fuel to run on. They state "95 Ron or higher"

Daz1121

I wasn't sure but always found it runs best on Optimax. But to save a bit a money as round this way Optimax is now at £1.015/l might try using 95RON unleaded at 95p/litre instead.

AVI-8

Your absolutely right guys but you wouldnt have bought a Subaru if you didnt like to put your foot down now and then would you.

And if you can get a few more bhp by spending 5p a litre extra then why not, its not as though 5p on a litre is going to make much difference to the astronomical price we pay for petrol anyway.

Couple of quid a week, christ you cant even buy a pint of beer for that

The Rig

iTrader: (13)

but if we all had that attitude, petrol would be £3.00 litre and we could still say, a pint of beer is this, yeah,but a pint of beer does a lot more id say !!!

ALi-B

iTrader: (1)

On the flip side, if you can't tell the difference between Carlsberg and Carlsberg Export, then why not save 50p and go for the normal Carlsberg? You'll still get p*ssed

If they made petrol, it would probably be the best petrol in the world.

So if you can'y feel or notice the extra 3-4bhp in the day to day driving, then why bother?

AVI-8

The Rig

Mate theres no-one more discusted at the huge tax that we pay on our petrol than me, I certainly didnt vote the imcompetent w!nkers back in a couple of years ago. Theres nothing that I can do as an individual to change the price of petrol

Im just saying that in the grand scheme of things a couple of quid a week is a small price to pay for having what I percieve to be a little bit more power. Some people pay thousands of pounds for a power increase.

BedHog

How? Presumably the only way is via the onboard knock sensor? Even then I can't imagine it making that much difference, especially if it was a UK car.

ALi-B

iTrader: (1)

It doesn't produce more boost. All it does is advance the ignition timing a few more degrees BTDC.

AVI-8

The ECU has maps for higher octane and lower octane fuels and the ECU selects between them depending on knock sensor activity.

The ecu also learns ignition timing from the knock sensor and sculpts these maps over time.

Pre 99 models retard the timing in an area of the map if the knock sensor was ever active, 1999/2000 models will try periodically to advance the ignition again, 2001 and later models run very activelly on the knock sensor and adapt very quickly

In essence if you have an older car and you run it on lower octane fuel, then change to higher octane fuel you wont immediatelly notice the difference in performance unless you reset the ecu, in 99/00 models it may take 20 or so miles to notice the benefit and on newer cars the benefits are noticed much more quickly.

If your car runs standard boost and its a cold day higher octane fuels may not give you much more than 3 or 4 bhp gain but modified higher boost on a warm summer day and believe me the difference is noticeable and is more than 3/4 bhp

RA Dunk

i saw that little test they did on fifth gear and all of the above is actually true optimax does make a significant increase on BHP and performance i cant remember what the exact figure was though

BedHog

http://en.wikipedia.org/wiki/Gasoline#Octane_rating

Long article but very good - explains octane ratings....

RA Dunk

Country USD/gallon Local measure As of Source United States $2.43/gal $2.43/gal March 2006 NPR/US DOE Japan $4.56/gal 134.9 yen/liter May 1, 2006 Japan Oil Information Center [7] United Kingdom $6.87/gal 96.13p/liter April 27, 2006 [8], Google exchange calculator on 15 May 2006. Saudi Arabia (Riyadh) $0.91/gal
March 2005 CNN Money/[9] Netherlands (Amsterdam) $6.48/gal
March 2005 CNN Money/[10] Norway (Oslo) $6.27/gal
March 2005 CNN Money/[11] Italy (Milan) $5.96/gal
March 2005 CNN Money/[12] Denmark (Copenhagen) $5.93/gal
March 2005 CNN Money/[13] Belgium (Brussels) $5.91/gal
March 2005 CNN Money/[14] Venezuela (Caracas) $0.12/gal
March 2005 CNN Money/[15] Nigeria (Lagos) $0.38/gal
March 2005 CNN Money/[16] Egypt (Cairo) $0.65/gal
March 2005 CNN Money/[17] Kuwait (Kuwait City) $0.78/gal
March 2005 CNN Money/[18] Malaysia (Kuala Lumpur) $2.01/gal RM1.92/litre February 2006 [19]/Google exchange calculator on 15 May 2006



well there you have it were definatly up there with the best of robbers and theiving ***** for governments , well done to us!



BTW Saudi looks a nice place to live $0.91/gal lol

BedHog

Yep we are the most expensive...

Venezuela 0.12$/Gal........

Sorry that link was a generic Petrol one.

http://en.wikipedia.org/wiki/Octane_rating

That is better for explaining Octane Rating..........

BedHog

HTH

AVI-8

Bedhog

You missed out the next line

Quote: Using higher octane fuel makes a difference when an engine is producing its maximum power.

It then goes on to demonstrate that on a particular engine that they tested lost 4% of its power wth a two octane decrease, they said that at higher altitudes because of decreasing air pressure, that the difference wouldnt have been so great, obviously this test was not on a turbocharged engine.

However Subaru's run at double atmospheric pressure under full boost, therefore the difference will be greater.

ALi-B

iTrader: (1)

Although boost pressure still remains the same as there is a change-over valve used that switch the MAP (manifold pressure senor) sensor to read atmospheric pressure. So boost pressure is always maintained at a fixed pressure in proportion to atmospheric pressure. So octane has no relevence in driving at different altitudes with a car that uses this method of electronically controlled forced induction (unless we're driving well over 10,000ft ).

C2forWRX

I aggree. Mine doesnt like it much eather (WRX PPP). Optimax is its favourite even if it is £102.9 a litre

BigAl024

Thats it, I'm moving to venezuela!!

yhe chod

that relates to europe if your car is a european import car[they call 95 ron super unleaded]

u can run it on 95 [normal unleaded]or 98 [optimax]
it will run safelyon a uk car[ jap imports need 100 ron unless they have been mapped to use uk fuel.].the ecu will adjust accordingly.but it will be rough on the 95 and smooth on the 98, in the scooby

optimax also cleans your valves and keeps it clean.

but what higher octane fuel will give you is less chance of detonation.
the higher octane gives it a higher temperature before it self ignites
in turbo cars u got high compression and high temps already- so higher octane aloows u more power to be produced before the ecu senses that there is detonation and retards the timing of the spark.
the higher the detonation threshold of the fuel[ie higher octane], the more power u can achive before any det.
remember its the job of the spark plug to initiate the igniting of the fuel not anything else like fuel,carbon deposits, or high cylinder temps

if its a wrx jap import u should be using 98ron [optimax] and a octane booster so the fuel would be 100ron. or ofcourse get the car mapped to use 95ron or 98ron [but 95ron mapped will have lees power]