The specified fuel for all Mk1s is 98/99. Higher octane = more energy, so, more mpg/mph. Not both, at the same time though!
Mac.

 

I normally run mine on 95 RON for comuting to work (mostly motorway), I get more miles to the £ but it does feel down on power. If i'm going out playing in it at weekend i put Shell V power in it and can really feel the difference in power.

 

I think your millage is more dependent on the amount of ethanol in the fuel. The more ethanol, the worse your millage. The ethanol will raise the RON rating, but lower the millage if the fuel company chooses to raise its RON rating that way.

Here in Canada, our RON is calculated differently, our 94 is about equivalent to the EU 98/99. One company here chooses to put out 94 w/o ethanol, my millage on that is about low to mid 30ies (and I drive with my foot 'in it'). Another company also puts out 94, but they raise the octane rating by the use of ethanol, so the TT millage on that fuel is quite worse. Here, lower the grade of fuel, the more ethanol it contains.

For the TT, Audi recommends RON 98. Any less, and the performance is cut back by the ECU to cope with the lower octane rating. Ideally, you want 98 w/o any ethanol content. Not sure if the TT components are ethanol proof (ei.) if they can cope with alcohol in the fuel lines.

 

I normally run mine on 95 RON for comuting to work (mostly motorway), I get more miles to the £...

Are you sure? I get 10% better MPG in a 2004 Subaru if I use RON 99 which costs 5% more, so in that car it's a no brainer.

 

The specified fuel for all Mk1s is 98/99. Higher octane = more energy

being picky, I don't think that's strictly true. A litre of fuel has exactly the same amount of 'energy' in it, no matter what. The additives that change the RON simply allow the timing to be shifted to enable the engine to work more efficiently... I think that's correct

 

150 are mapped for 95RON
Not sure about 180
225, QS & V6 all mapped for 98RON

I always run my V6 on Super Unleaded, usually Tesco 99RON.

Very soon 95RON will become E10 in the UK (10% Ethanol), Super Unleaded will remain E5.

 

PlasticMac is correct... more Octane = more energy. BUT... A fuel company will add extenders, like ethanol to the fuel. That will raise the octane, but the extender has lower energy content so less performance or more fuel burned to generate same energy content. Check what is put into the fuel you buy... not just the RON number.

 

PlasticMac is correct... more Octane = more energy

No - I don't think so

oooh dear I've only been here 20 posts and I'm already causing trouble.

 

I normally run mine on 95 RON for comuting to work (mostly motorway), I get more miles to the £...

Are you sure? I get 10% better MPG in a 2004 Subaru if I use RON 99 which costs 5% more, so in that car it's a no brainer.

Yes i'm sure as round here Shell V power is about 15% more than Morrisons 95
I can check actual price on my way home.
For a normal weeks comute i would put £40 of 95 in and would be about £45 of V power so saves me about £20 a month

 

I normally run mine on 95 RON for comuting to work (mostly motorway), I get more miles to the £...

Are you sure? I get 10% better MPG in a 2004 Subaru if I use RON 99 which costs 5% more, so in that car it's a no brainer.

Yes i'm sure as round here Shell V power is about 15% more than Morrisons 95
I can check actual price on my way home.
For a normal weeks comute i would put £40 of 95 in and would be about £45 of V power so saves me about £20 a month

Ahhh right - understand. We can get Tesco/Greenergy RON 99 which is only 5% more than their 95. So we are both correct

 

The specified fuel for all Mk1s is 98/99. Higher octane = more energy

being picky, I don't think that's strictly true. A litre of fuel has exactly the same amount of 'energy' in it, no matter what. The additives that change the RON simply allow the timing to be shifted to enable the engine to work more efficiently... I think that's correct

I believe (doesn't prove anything) that you get more energy *calories/joules or whatever) out of higher octane fuel, as the burn starts nearer TDC on the compression stroke, so more bang on the down stroke.
Mac.

 

I think your millage is more dependent on the amount of ethanol in the fuel. The more ethanol, the worse your millage. The ethanol will raise the RON rating, but lower the millage if the fuel company chooses to raise its RON rating that way.

Here in Canada, our RON is calculated differently, our 94 is about equivalent to the EU 98/99. One company here chooses to put out 94 w/o ethanol, my millage on that is about low to mid 30ies (and I drive with my foot 'in it'). Another company also puts out 94, but they raise the octane rating by the use of ethanol, so the TT millage on that fuel is quite worse. Here, lower the grade of fuel, the more ethanol it contains.

For the TT, Audi recommends RON 98. Any less, and the performance is cut back by the ECU to cope with the lower octane rating. Ideally, you want 98 w/o any ethanol content. Not sure if the TT components are ethanol proof (ei.) if they can cope with alcohol in the fuel lines.

I saw (on the A2OC Forum) what seemed to be an official VAG doc, that listed those cars incompatible with E10 (10% alcohol) fuel which is coming here in UK. The Mk1 TT weas not on there (so, in theory is OK). My 1.6 A2 FSI, is on there as incompatible, but OK on E5 (5%). Annoyingly, they give no information as to why the 1.6FSI does like E10.
Personally, I'll stick with E5 V Power, as long as my pension holds up!
Mac.

 

Higher octane = more energy

The above is a common misunderstanding but is not necessarily true. The octane rating (RON /MON) is a measure of the fuel's resistance to detonation, not the amount of energy it produces. The latter is given by its calorific value (which the oil companies are not required to state). As it happens, higher octance 'petrol' also tends to have a higher calorific value but this is not guarranteed. A good example is LPG, which has a higher RON than petrol but a significantly lower calorific value. Typically you get around 33% less mpg on LPG because of this.

A further complication is that a higher RON would allow you to re-tune the engine slightly to gain a little more power/torque, but this is an increase in the efficiency of the engine not anything to do with the energy of the fuel (but see previous comments about higher RON petrol).

 

OK, turning it on it's head, given that our engines are tuned (OEM) for 98/99, and, ignoring cost and mpg, it is generally accepted that the cars perform better on 98/99 than on 95, why is that?
Mac.

 

Mine does and it's really noticeable. Why? Probably because they are set up to run on the higher octane.

When on the lower octane the ECU adjusts the timing to prevent knock so i believe

 

Mine does and it's really noticeable. Why? Probably because they are set up to run on the higher octane.

When on the lower octane the ECU adjusts the timing to prevent knock so i believe

Hi, Correct, Ign timing is retarded to prevent knock (pinking) so efficiency & power is reduced to protect engine.
Hoggy.

 

.......
For the TT, Audi recommends RON 98. Any less, and the performance is cut back by the ECU to cope with the lower octane rating......

The ECU has no idea what rating the fuel is and relying on the engine knock sensors to cut the timing and add extra fuel to try and save the engine when it detects detonation is crazy, at 6000 rpm each cylinder has 50 explosions a second... why would anyone risk putting low grade fuel and making the ECU focus on reactive survival.

Its not pulling timing to prevent knocking its reacting to the engine knocking and pulling the timing, reducing the load and adding extra fuel, to try and stop it knocking... Instead of just enjoying itself..

...
When on the lower octane the ECU adjusts the timing to prevent knock so i believe...

This is why some people with a simple stage 1 map, so bend rods - I made the mistake of putting normal unleaded in my s3 and a spark plug ceramic split in half the same day.

 

What I am not sure is how each cylinder detection of pre-ignition detonation is detected. There's several maps eg 'degree of timing retard per knock event' but that ranges from 0 to -12.75 they don't have to be added up.

And enrichment per knock event, also another map of ignition adjust based on lambda eg on a stock engine and not WOT if a knock event has occurred, that may adjust the timing by reducing +15 to +12, and as a knock event the fuel is enriched to cool the cylinder and because the lambda is now maybe 0.92 then another 2 degrees of retard. And with 'continous knock' (no idea how that is measured - what constitutes 'continous' ? 2 events in a row or knocking for 10 seconds?) the load can be massively reduced. This Map on the BAM and AMK the load is reduced, the QS BFV engine actually increases the load, probably to counteract the timing being pulled, otherwise people will notice a sudden drop in power from 240ps to 205ps or whatever, so maybe they just allowed the knock to continue and be controlled by timing and enrichment?

 

OK, turning it on it's head, given that our engines are tuned (OEM) for 98/99, and, ignoring cost and mpg, it is generally accepted that the cars perform better on 98/99 than on 95, why is that?
Mac.

Because the ECU retards the ignition when you run it on 95RON. (Meaning it's fires the spark later)

Being able to run more ignition advance produces more power.
With exotic race fuel you can dial in ridiculous amounts.

 

LoL... "Somebody opened a can of worms"...

To summarize things... The optimal RON rating for the engine is 98 so it operates at designed efficiency. The fuel suppliers can meet that requirement through pure gasoline, or gasoline blended with ethanol. The fuel blended with ethanol - while it meets RON 98 requirement, it contains less BTU/energy, so you need to burn more of it to obtain the same amount of power as non-blended fuel. Hence, worse millage on blended fuel.

However, financial cost needs to be worked out on an individual basis, as that depends on the % of the blend, the cost of the alternative and the value of the differential factors. It may be cheaper to run blended fuel if the blended fuel is cheap enough to offset the millage differential.

Now... lets NOT get into a discussion what ethanol does to your fuel if you let it sit for too long... [smiley=devil.gif]

 

You'll struggle to find any Petrol with 0% Ethanol in Europe.

 

You'll struggle to find any Petrol with 0% Ethanol in Europe.

We know, that in UK, 98/99 Ron has 5% alcohol, and 95 Ron has (or soon will have) 10% alcohol.
From JoeKan's info above, 98/99 (UK) Ron wins, as lower alcohol = more energy. This is what I suggested originally ...
Mac.

 

The specified fuel for all Mk1s is 98/99. Higher octane = more energy

being picky, I don't think that's strictly true. A litre of fuel has exactly the same amount of 'energy' in it, no matter what. The additives that change the RON simply allow the timing to be shifted to enable the engine to work more efficiently... I think that's correct

....you said the above

Higher octane does not equal higher energy.

More additives may well = less energy, but that's not the point as ethanol is currently 5% across the board?

 

150 are mapped for 95RON
Not sure about 180
225, QS & V6 all mapped for 98RON

Thanks - I think that was my original question answered I should try and phrase things better. My VAG knowledge runs out after 1996.

 

The fuel filler on my 190 specifies 95 - 98 Ron/Roz. The handbook recommends 98 Ron, or 95 Ron, with slight power loss. Same for all engines except the 150, where 95 Ron, or 91 Ron, with slight power loss is recommended.
All those Ron ratings are pre alcohol off course. 98/99 E5 probably equates to around 96/97 pre alcohol I'd guess. So, when 95 E10 arrives, we will probably notice the difference in performance.
98/99 E5 will get dearer, and harder to find over the next few years I guess. Hey ho,
Mac.