different types of fuel in a gti?

[lexie]

this might sound stupid but could someone explain the effect of running lower octane fuel in a mk5 gti? i know turbo'd cars should be fed the 'good' stuff but why? is there long term damage done to the engine or just mpg figures?

[speedynz]

Without getting too technical (this is a brilliant subject for it) just run your engine on the good stuff.

BP Ultimate will give more power, better MPG and sharper throttle response than standard 95octane.

It is also the cheapest horsepower (and torque) increase you will get.

In EVO magazines test of different fuels a standard MK5 GTI running on BP ultimate gave a peak of 252lbft of torque, a full 20% better than the manufacturers quoted output.

Other members may have seen good results with other fuel (Tesco 99 octane etc) but for my money BP Ultimate is the best readily available forecourt fuel you can buy.

[speedynz]

I am not a paid spokesman for BP or any of it's affiliated businesses!!!

I just rate it!

[Teutonic_Tamer]

this might sound stupid but could someone explain the effect of running lower octane fuel in a mk5 gti? i know turbo'd cars should be fed the 'good' stuff but why? is there long term damage done to the engine or just mpg figures?

Two separate issues arise from running on lower octane fuel in all FSI engines.

Firstly, the lower octane will cause earlier pre-ignition, detonation or knocking.  This will retard the ignition timing, giving lower performance, and increased fuel consumption.

Secondly, ignoring the retarded ignition timing, lower octane will also increase fuel consumption, due to the fact that the "stratified", or lean burn mode will be operating less. 

[Teutonic_Tamer]

BP Ultimate will give more power, better MPG and sharper throttle response than standard 95octane.

As will all super unleaded petrols.

It is also the cheapest horsepower (and torque) increase you will get.

Not in the UK.  BP Ultimate is THE most expensive super unleaded, and isn't really a super unleaded at all - because it is only rated at 97RON, when the EU standard for super unleaded is 98RON.

Tesco99 is the cheapest super unleaded, and like Shell V-Power, are the only fuels in the UK to be rated at 99RON. 

In EVO magazines test of different fuels a standard MK5 GTI running on BP ultimate gave a peak of 252lbft of torque, a full 20% better than the manufacturers quoted output.

But that result was not conclusive, was not statistically correct, and certainly did NOT match independent tests.  Tesco99 was proven to provide the largest power gains, and was clearly better than BP Ultimate, and also the now obsolete Shell Optimax.

Other members may have seen good results with other fuel (Tesco 99 octane etc) but for my money BP Ultimate is the best readily available forecourt fuel you can buy.

But that is a New Zealand perspective, and doesn't reflect UK prices.   

[Teutonic_Tamer]

I am not a paid spokesman for BP or any of it's affiliated businesses!!!

Quick - hide your BP lapel badge !!!!       

[speedynz]

The EVO test was independent, it clearly showed that BP Ultimate (97 octane in UK, sorry, my mistake) produced the same power as Tesco 99 octane but significantly more torque and indeed more torque than even Sunoco race fuel (albeit a little less power than that racing cocktail).

The tests were carried out in a highly methodical manner and in a carefully controlled enviroment and proved conclusively that the higher octane fuels gave better performance.

They also showed that bad batches of fuel (of which they encountered many) could show appalling results relative to 'fine' fuel. The tests were lengthy and entirely without predjudice.

Subjective analysis was also portrayed and again BP was a great performer, although not perfect and not alone in producing a sharper feel to the throttle.

I do not understand your statement that the tests "were not statistically correct". How so??

My statement about the horsepower increases being "the cheapest that you can get" were meant to be relative to coventional forms of tuning, not relative to the cost of other brands of fuel. Although I do understand that you pay up to 15pence per litre more for higher octane fuels than for regular (95) octane. In New Zealand we pay about 2pence per litre premium for 98 octane BP Ultimate over the cost of regular 95 octane.

I wonder why in New Zealand we get 1 octane more than the UK out our BP fuel??

My personal experience is very clear and backs up that of the independent tests. BP Ultimate is a measureably better fuel than any other on sale of here. Depending on ambient conditions and batch irregularities it can feel like a 10-15% improvement in performance.

TT, I know that at heart you are a 'Total' man, I have to admit that there is a whiff of mystique about this underrated petroleum company but aside from that I have never been given any reason to believe their product is any better than everyone else's. Whereas with BP Ultimate I have.

[Teutonic_Tamer]

speedy, do you have a URL for the EVO test?

What laboratory carried it out?

I stated it wasn't statistically correct, because from memory, they never had a "control" car, nor did they use a "control" fuel.  They didn't list the full atmospheric conditions for each dyno run, and I don't remember them even being done at the same time (though I could be wrong).

Regarding "feel to the throttle" that is pure and simply subjective, and not at all scientific.  A dyno run, coupled with live ECU data logging will categorically prove the "throttle response vs throttle request" - but without that kind of data, their statement is meaninless and flawed.  Afterall, not everybodies "butt dyno" is calibrated the same! 

Oh, and I don't know where you got I was a "Total" man from?  I just use quality branded fuels with the highest octane available.  In the UK, that is Tesco 99 or Shell V-Power.  In Germany, it will be Aral (BP) Ultimate 100.  In France, all their supers seem to be 98 RON, but my own "butt dyno" suggests Elf/Total to be better than others (probably because they are a French oil company).

[speedynz]

TT, I like people that know their red onions from the less desireable brown variety.

PM me your home address and I will mail you the article in full, at the very least it will be a 'happy' piece of post in amongst your phone bill and insurance renewal notification.

This is a complex subject, even before we start talking 'Hyrocracking', 'Hydrocarbons', relative octane weights, numbers and additive capability relative to ECU timing adjustability. So let's keep it simple.

Read the test, stand back, throw off your cynical gown (I own a few of those myself) and try to tell me that you're not convinced.

Yes, you could pick holes in it, but only if you really have to.

This is a great 'real world' article and combined with my own wholly unscientific experiments over the last 10 years backs up my understanding of these fuels.

As an aside, a friend of mine recently put 20 litres of pure 'Toluene' in his 12 month old Megane 225, this additive was used at an 85% ratio in the Formula 1 cars during the high power turbo era to incredible effect. He ran it at a 50% ratio, came and picked me up, took me up the road and.............well, nothing actually, not a blind bit of difference.

[Rhyso]

I stated it wasn't statistically correct, because from memory, they never had a "control" car, nor did they use a "control" fuel.  They didn't list the full atmospheric conditions for each dyno run, and I don't remember them even being done at the same time (though I could be wrong).

if i remember correctly they used a Golf GTI and a BWM 5 series petrol (could be wrong on that one) but do you mean in that they should have used 2 GTI's, one with standard 95 ron and the other using the super unleaded stuff?

Both were put on the dyno at the same time