Super or regular?

[Teutonic_Tamer]

i've used super all but about ten times in my impreza wrx- tbh i've noticed very little difference in it power/ fuel economy, and the filler cap says 98+.

Yes, but what type of 'super'?  Becauase they aint all the same.  Most supers in the UK are actually only 97 RON - so hardly an increase over the standard 95.  But Shell V-Power and Tesco 99 are both 99 RON - which is really quite a difference over 95 RON.

Secondly, because you 'normally' use 95, then your ECU has probably 'adapted' to run with less advance on the timing as its 'default' settings - and when you do occasionally give it a splash of super, the ECU doesn't have long enough to properly adapt, before you end up slinging poverty-spec juice at it again! 

in fact running a tank of 95 after 98/99 seems to be better if anything- but the scoob doesn't have a range computer- just a rather uneven fuel gauge.

That IS a well known phenomenom in that scenario, across most makes of car.  The in-depth answer is a bit 'tecchy'.

i'll probably give the gti a test and if i see a benefit out of super i'll use it, otherwise i'm planning to go back to regular

If yours is a Mk6, then it would seem you may not actually notice any benefit with super.    With a remap though, that is different!   

I use shell v-power or tesco 99, only buy super from bp/esso/ total if i have to and 95 only if i'm out in the sticks with no alternative- so think you got the wrong end of the stick- very little poverty fuel for me!

i was assumed the ecu still thought it was on the good stuff when i put in the normal, but don't understand why it seemed to be better on fuel then?

OK, I'll try and explain.  Modern ECUs are 'adaptive' (sometimes called 'fuzzy logic') - and this means that as well as providing 'instructions' (for how much fuel to inject, when to inject, what advance on the timing, etc) - they also need to 'learn'.  They learn by 'reading' information - the most obvious are things like the MAF, crank and cam position sensors, knock sensors, and the likes (and they also learn throttle pedal actuation, brake pedal actuation, and even steering inputs if ESP is fitted).  So once they have learned this stuff, which normally needs at least a couple of engine off/engine on cycles - the ECU can then store a slightly revised 'default' setting.

So if you normally use 99 RON, and drive hard making full use of the '99 RON performance' - the ECU will adapt to provide that level of performance as a default.  But then if you stick some 95 RON in the tank - the ECU doesn't get 'told' that you have put 95 RON in - and will continue to try and deliver the 99 RON performance.  It will initially try to do this by advancing the ignition timing, but the knock sensor will be constantly instructing to retard the timing - so it then trys the next thing - which is to inject more fuel - creating a richer mixture, which is less prone to knocking.  Because the engine continues to 'behave' with an increased fuel delivery rate - the engine will appear to perform the same as if it were still using 99 RON - but the ECU will still know that something now isnt quite correct - but still stores some new 'learnings'.  Then you get home, park up, turn off the engine, eat, drink and go to bed.  The next time you start the engine, the procedure happens all over again - but this time - has already 'learnt' that it needs less advance, and also 'knows' that it shouldn't have been injecting that much fuel as yesterday - so the performance will progressively drop to suit the 95 juice.

And the same happens in reverse.  If your ECU has been used to 95 - by then filling up with 99, you arn't gonna get any increase in performance until the ECU has had a couple of 'cycles' to learn the new settings and adapt accordingly.

Does that help? 

[AudiA8Quattro]

Interesting reading.
Have ecu's always been so adaptive, or is it only newer ones?

[Teutonic_Tamer]

How many times? Because it has more octane in it which the FSI engine is designed to run on (runs for longer in FSI mode, this has all been said and I cant be assed to find the link). It has cleaning agents in which help keep your engine cleaner, thus more efficient. You get more MPG. Your meant to get more power (all be not much) etc etc etc. You just have to decide if you want to spend that bit more on your fuel or not, it will run perfectly well on 95.

Yes, yes - I agree with all that.  But you seem to be forgetting that Audi have developed the latest TSI Mk6 engine to now achieve maximum economy with just 95 RON.  So by simply slinging 99 at it will NOT give you any further improvements in fuel economy.  The ONLY time using 99 would give improvements in power and/or economy is if it was remaped.

The cleaning agents issue is not so clear cut.  Yes, it is generally accepted that the higher quality super unleadeds, such as Shell V-Power, Tesco 99, BP Ultimate, Total Excellium, and the Esso one (whatever it is called!) - all have an 'increased' detergents package.  I purposely exluded Sainsburys 97 super unleaded from that, simply because I can find no evidence it has an increased additives pack over its standard 95 unleaded.  But is there any hard and fast proof that the standard 95 unleaded from those above, albeit with slightly less detergents, actually causes any noticable build up?    BP, or Shell, or Esso or the other main oil companies are not going to sell 'sh!t' fuels - and they also rely on their 'brand image' too.    Whereas - let's say Asda - they are well known for being cheap and basic - and I would also assume their fuels are also 'cheap and basic'.  Which is why, when it comes to normal 95 unleaded, with the exception of Tescos (who's fuel is easy to check, because it is made by GreenErgy) - all supermarket fuels should be avoided - because they may not have the same levels of additives (including detergents) as the unleadeds from the normal oil companies.

Sorry, Im a bit ratty as its a million degrees in my office.

Tell me about it, I'm roasting my nads off! 

[Teutonic_Tamer]

Like all older gti's/vr6's with electronic fuel injection systems, they are set up to run on 98 RON, but will run perfectly on 95 RON with knock control.
Obviously using 95 RON can lead to a small loss of power. The higher the RON figure, the better the fuel can resist detonation, hence being able to advance the ignition timing.
Is this correct?

Your theory is spot on correct - but the new Mk6 GTI as been set with a default base setting for 95 RON.  So will not be able to advance the timing far enough to utilise the max potential of any 97/99 brew.  HTH



LOL - very off topic - just watching the weakest link, and some contestant works for VW marketing, and she was stating that 'Dave' (meaning independent garages) are a bit 'gruff and grumpy' - wonder where she got that from? 

[Teutonic_Tamer]

Interesting reading.
Have ecu's always been so adaptive, or is it only newer ones?

It is generally just the newer ones.  All Bosch Motronics are adaptive, whereas their earlier Digifant and Jetronics were not.  Obviously, as the different Motronic 'generations' have advanced, they can do more and more things - but they still can't cope with high engine revs.  High revving B7 RS4s, R8s and C6 RS6s now need two separate Motronic ECUs - although they both work together, and both have some 'redundancy' back-up for each other! 

[Rolfe]

How many times? Because it has more octane in it which the FSI engine is designed to run on (runs for longer in FSI mode, this has all been said and I cant be assed to find the link). It has cleaning agents in which help keep your engine cleaner, thus more efficient. You get more MPG. Your meant to get more power (all be not much) etc etc etc. You just have to decide if you want to spend that bit more on your fuel or not, it will run perfectly well on 95.

But you seem to be forgetting that Audi have developed the latest TSI Mk6 engine to now achieve maximum economy with just 95 RON.  So by simply slinging 99 at it will NOT give you any further improvements in fuel economy.  The ONLY time using 99 would give improvements in power and/or economy is if it was remaped.

You see my confusion?

Rolfe.

[ub7rm]

How many times? Because it has more octane in it which the FSI engine is designed to run on (runs for longer in FSI mode, this has all been said and I cant be assed to find the link). It has cleaning agents in which help keep your engine cleaner, thus more efficient. You get more MPG. Your meant to get more power (all be not much) etc etc etc. You just have to decide if you want to spend that bit more on your fuel or not, it will run perfectly well on 95.

But you seem to be forgetting that Audi have developed the latest TSI Mk6 engine to now achieve maximum economy with just 95 RON.  So by simply slinging 99 at it will NOT give you any further improvements in fuel economy.  The ONLY time using 99 would give improvements in power and/or economy is if it was remaped.

You see my confusion?

Rolfe.

I think TT has removed the confusion.  The strong argument put forwards by us mk5'ers was that high octance fuel increased both performace and MPG, which was true for the mk5 engines.  TT has explained why this is no longer true for the mk6.  You lucky buggers.

Edit  :embarassed:

[Teutonic_Tamer]

How many times? Because it has more octane in it which the FSI engine is designed to run on (runs for longer in FSI mode, this has all been said and I cant be assed to find the link). It has cleaning agents in which help keep your engine cleaner, thus more efficient. You get more MPG. Your meant to get more power (all be not much) etc etc etc. You just have to decide if you want to spend that bit more on your fuel or not, it will run perfectly well on 95.

But you seem to be forgetting that Audi have developed the latest TSI Mk6 engine to now achieve maximum economy with just 95 RON.  So by simply slinging 99 at it will NOT give you any further improvements in fuel economy.  The ONLY time using 99 would give improvements in power and/or economy is if it was remaped.

You see my confusion?

Rolfe.

Huh - AlanD was quoting from how the Mk5 GTI was set up, whereas my answer was for the Mk6!

So in a Mk6 GTI - max economy will be gained with 95 RON.

[AudiA8Quattro]

How many times? Because it has more octane in it which the FSI engine is designed to run on (runs for longer in FSI mode, this has all been said and I cant be assed to find the link). It has cleaning agents in which help keep your engine cleaner, thus more efficient. You get more MPG. Your meant to get more power (all be not much) etc etc etc. You just have to decide if you want to spend that bit more on your fuel or not, it will run perfectly well on 95.

But you seem to be forgetting that Audi have developed the latest TSI Mk6 engine to now achieve maximum economy with just 95 RON.  So by simply slinging 99 at it will NOT give you any further improvements in fuel economy.  The ONLY time using 99 would give improvements in power and/or economy is if it was remaped.

You see my confusion?

Rolfe.

Huh - AlanD was quoting from how the Mk5 GTI was set up, whereas my answer was for the Mk6!

So in a Mk6 GTI - max economy will be gained with 95 RON.

You stroppy bastard 

[R32UK]

thanks TT!!! you have just convinced me I will defo need a remap