Fuel Consumption figures

[DavidT]

I think we need to start a separate thread if we're going to get into discussing the merits of available fuels...

I think you're right about that, thanks Clive.

[CliveH]

Did the article mention anything about the effects on MPG?

[saf]

I think that the fuel scores may vary for each car.

May be better for a cosworth but not for an S4?

I would have thought that because I drove with optimax for quite a while.

When I changed to Tesco 99, I felt a difference in acceleration atraight away. It was an immediatedifference.

Maybe on the cosworth, and the way it works, Shell optimax is better.

[tartan_rob]

In theory - the make of fuel makes no odds. Higher octane fuel should be more explosive full stop.

FYI - the V6 S4 block has was tuned by cosworth. I have gone back to OPtimax from using Tesco, I found tesco's fuel was loosing me MPG.....or perhaps that was heavier reight foot...LOL.

[GrimReaper]

Did the article mention anything about the effects on MPG?

will try and find the original source to see what it says think it was just a bhp figure guide tbh.

I have so far found BP ultimate better for MPG for my style of driving. Optimax is fine for normal journeys but my right foot can be heavy at times and thats probably why i only got 168 miles to £45, damn those quiet B roads Not able to compare with Tesco 99 as not seen it available yet down in the deepest depths of Cornwall.

[KayGee]

In theory - the make of fuel makes no odds. Higher octane fuel should be more explosive full stop.

Common miss conception, higher octane rating means it is less likely to ignite, or more importantly less prone to pre-ignition and knocking. This means more power (more boost, more aggressive timing, etc...) can be extracted before the onset of knocking and/or pre-ignition.

Putting 99 Octane in a car correctly tuned for a lower octane will offer no improvement in performance. It needs to be retuned for the higher rated Octane fuel. In the S4s case it will learn within the trim ranges available adjustments.

HTH

Kevin

P.S I use Tesco 99 as it's available and cheap.

[Paulm]

Got to agree with Kevin. You take LPG its octane value is 103 ron but its calorific value is less the 95 ron so = less power but more knock protection.

[Dippy]

Adding to Kevin's post, in addition to being less likely to pre-ignite and therefore allowing more advance to be used, the higher octane fuel burns slower. This means that indeed more energy can be converted thus increasing torque, but also that conversion is smoother so there is less shock to the engine overall.

[KayGee]

Wow two common miss conceptions in one thread...we're on a roll this week.

n addition to being less likely to pre-ignite and therefore allowing more advance to be used, the higher octane fuel burns slower.

Octane rating and burn rate are not related, burn rate is a function of several variables, and the two are completely independent. There does tend to be a correlation between higher octane and slower burn rates but that is due to manufacturers blending their products that way.

Sunoco maximal has 116 Octane rating (ron+mon/2) but has fastest burn rate of all their race fuels.

Burn rate is particuarly important with regard to high rpm engines. You need a fuel that ignites in the quickect possible time when your engine is spinning really fast. This factor can have a large effect on what petrol works in one car really well and not well in another.

[Dippy]

Of course returning to the original subject of this thread, for most members who buy their fuel from common sources there is indeed a correlation between higher octane and slower burning.

For others like KayGee who buy Sunoco maximal, you can be happy that you know that the two parameters are indeed independent.

[KayGee]

I wish I could 1. Get it and 2. afford it...tescos 99 for me.

[harry]

and there aint even a Tesco in Scotland that supplies 99 in my experience