Petrol types

Post by **vw_nutta** » Sun Jun 27, 2004 11:37 am

what is the favoured petrol for the 2.7tt?

Not neccessarily which petrol produces faster results but which is actually better for the engine?

Shell Optimax or usual 95ron unleaded?

Post by **DaveP** » Sun Jun 27, 2004 11:50 am

Try a search for Optimax...this has been discussed several times....I only ever put Optimax in (unless I really get stuck!)

Post by **DavidT** » Sun Jun 27, 2004 1:31 pm

I use Optimax with a bottle of millers octane booster.

I noticed the car was less responsive with normal unleaded. Not sure about the power output differences, but they tell me Optimax+millers = 100 octane so that should help!

Post by **ajsl** » Sun Jun 27, 2004 7:24 pm

Optimax here too

Post by **Nige_RS4** » Mon Jun 28, 2004 9:08 am

Optimax + Millers =

Post by **Nordschleife** » Mon Jun 28, 2004 9:40 am

vw_nutta wrote:what is the favoured petrol for the 2.7tt?

Not neccessarily which petrol produces faster results but which is actually better for the engine?

Shell Optimax or usual 95ron unleaded?

Never, ever put 95RON in the car - it is bad for the the engine. The German manual advises against this.

Optimax, or its successor, VPower work best, it usually takes about a tank full to notice the difference, and its most obvious when running at maximum speed, noticeable more pulling power at the top end.

Petrol deteriorates. i know an Esso station next to the Refinery close to Ingolstadt, their 98 is as good as Shell's Optimax. The difference is, that the Esso 98 has to be bought from the 'first station the tanker goes to', whilst VPower is pretty good from any of the filling stations.
Its a good idea to go to a busy station, the more frequently the tanks are filled, the better, more likely to be up to spec and to have clean unpolluted tanks.

R+C

Post by **Dippy** » Mon Jun 28, 2004 12:20 pm

But the UK manual does not, because Audi know that 95 RON is the most common flavour in the UK. UK cars are specifically mapped to be able to <beep> the ignition to prevent knocking with 95 RON.

However I'd agree that 95 RON should be only used for 'emergencies' and the car not driven too hard with it.

Post by **BlackShadow** » Mon Jun 28, 2004 5:01 pm

What about if you stick 97 Ron petrol in it? That seems more widely available, and the difference to Optimax doesn't seem that great (i.e. 1 ron)? I try to stick Optimax in mine, but occasionally you can't always find a Shell station if you are in an area of the country you are not familiar with, and then the 2nd best seems to be super unleaded 97 ron thingy.

Post by **vw_nutta** » Mon Jun 28, 2004 7:33 pm

theres a shell garage near me so I should be ok then. I've got a mk3 golf vr6 at the mo, and have tried normal vs optimax and its amazing how more urgent the car feels. I also did a run home in the vr6 from being on holiday and put in one of the nitrox booster things, went well fast, couldn't believe the difference. The only thing I always wondered was whether I was actually benefitting the engine or just wearing it out quicker.

cheers, I'll be sticking to optimax where possible.

Post by **monty** » Mon Jun 28, 2004 8:37 pm

Always use optimax in the scoob!! Shell guarantee it at 98 octane, but it can be as high as 98.8!!!

dave

Post by **Dippy** » Tue Jun 29, 2004 1:40 pm

For those who don't know...

Audi optimised the engine for 98 RON because that is standard in Germany. However the ECU has dynamic control of the engine and can make adjustments for the actual octane used.

The octane of a fuel is effectively a measure of how slow/smooth it 'burns'. A higher octane fuel does not contain any more energy than a lower octane fuel, however it will burn more slowly and smoothly. This allows the energy to be released over a longer period, and if the engine timing is right, this means that the energy is used more efficiently.

Timing is key, because if the fuel/air mixture explodes before the pistons are in the correct position, the energy will either not be harnessed properly, or in the worst case it acts against the engine itself. This latter effect is known as 'pinking' or 'knocking'. Knocking is bad, which is why the 2.7TT (like most modern engines) incorporates knock sensors. If knocking is detected, then the timing is retarded to stop it.

Optimum performance comes from a timing which is 'on the edge' of knocking. So the higher the RON, the better the engine performance.

So although the engine is optimised for 98 RON, if 97 RON is used, the timing will be retarded to avoid knocking. As a result you will have a less than 265PS engine (in stock form). If you use 95 RON the timing will be severely retarded with corresponding loss of torque. More importantly since 95 RON fuel does not burn smoothly, the anti-knock mechanism will not be as precise. This means that despite the ECU's best efforts, with 'spirited' driving, you may get some pinking with 95 RON and this is not good for the engine in the long term.

Post by **SimonS4MTM** » Tue Jun 29, 2004 1:45 pm

Just one correction,

Pinkng or knocking is caused when the fuel ignites before the plug fires, RON is also relates to the fuel ability to not self ignite.

The timing is retarded is pinking or knocking is sensed to <beep> the ignition so that the plug fires sooner, preventing pre-ignition.

Post by **Dippy** » Tue Jun 29, 2004 1:57 pm

Simon,

I must disagree with you there. Pinking/knocking is the effect and not the cause. Whilst dieseling can cause it, so can other forms of mis-timing.

I was keeping my description simplified for the less technical members.

Post by **SimonS4MTM** » Tue Jun 29, 2004 4:51 pm

No problem

Post by **vw_nutta** » Tue Jun 29, 2004 10:04 pm

thanks for keeping it simple, damn I've got to go and do a night course in engine mechanics.

Pick the S4 up on saturday, yey!

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