Correct fuel type for Octavia RS

[brad]

The 1.8tsi Octavia (not the Scout) is in a relatively low state of tune compared to the 1.4 or the 2.0 engines and can supposedly be run on 91 Octane but the fuel sold in Aus is not great quality and still has relatively high proportions of sulphur compared to Europe.
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My 118kw 1.8tsi says 95ron minimum on the fuel flap.

Running 91ron (stupid dealer owed me a tank of fuel and then added 50L of 91ron) results in a noticeable decrease in torque over a smaller rev range and an increase in fuel consumption from about 6.5L/100km to 7.5L/100km under the same running conditions. I assume this is because the ECU pulls timing and increases fuel flow to compensate for the reduced octane.

More importantly, while the power returns almost immediately after filling with 98 ron, it takes around 2 tanks of "the good stuff" (say 1000km) for the MED17 ECU to restore the fuel economy.

I think most important is the cents per kilometre figure. On my car, it's pretty much the same whether it be 91ron, 95ron or 98ron. At current prices that's around 8-8.5c/km

[woofy]

I guess the engine has changed from my older TFSI so if they can now run more power on 95 rather than the 98 my current one needs than its pointless running 98. I've had pinging/diesel knock with the Caltex vortex diesel which I thought would be a good idea to run as its only marginally more than the low grade diesel, so using the Vortex 98 probably makes bugger all difference on the Mk3 if it ignores any octane higher than 95.

[Gerrycan]

A few random thoughts:
I think the new Ford Focus Ecotec 1.6 turbo and the Hyundai new turbo ranges are designed for US low quality fuel and they claim quite high outputs and are able to run on 91 Octane. Goodness knows how they do that.
Apparently all Australian official fuel consumption tests are required to be run on 95 Octane (not sure what is done with regards to those cars requiring 98 Octane?).
Finally, I have yet to see a properly run test that proves there is substantially better performance running an unnecessarily high octane.
I am excluding those dyno tests for tuned engines.
I remember the old Shell tv adverts of my Pommie youth where car "A" with Shell always ran 5+ mpg better than car "B" with the competitors product. The advertising focus now is more on the better detergents in the higher grades will keep your engine running cleaner/better/more economically. Might be something to do with more truth in advertising required these days (Fatblaster apart)?

[Tuan]

Doesn't answer all the questions but a but good read nonetheless since it's an actual real life scenario

Unleaded vs E10 - the comparison test | CarsGuide

Once your car is tuned, it's a different story ... best to stick with 98 (and some tuners swear by BP Ultimate).

[Gerrycan]

I am afraid that article is typical of its type. The general background info is accurate but the methodology of the "test" is so flawed it makes me cringe.
I drive a particular short (13 km) urban route in Adelaide and on the same fuel (even on the same tank) the consumption can vary by over 100% depending on traffic and environmental conditions. My best is 4.2 L/100 and worst is 8.5 L/100 and both were driven with an eye on economy. The higher consumption was probably the better effort because I had to use the air conditioner and traffic was terrible. The lower consumption was at night, but I still had to stop at 5 red lights so I could have done even better with a bit more luck.

Unfortunately Julian Edgar at autospeed.com has never done a fuel type comparison (that I can find) but his home spun testing methodology for his car mods (economy and performance) is about as good as you can get outside a laboratory.

[Tuan]

Which part of the test makes you cringe ?

[brad]

Which part of the test makes you cringe ?

Using suburban running to test fuel consumption.

There are too many uncontrolled variables. The only way to do it properly is using a rolling road.

[Tuan]

Look at what VW managed to do with their emissions testing in a controlled environment..

I do see the point in doing it in a lab/rolling road but we don't live/drive our cars in a controlled environment so a real road test in a daily driver gives good enough information for me.

[Gerrycan]

Which part of the test makes you cringe ?

Brad got it in one.
Using a rolling road would eliminate the majority of the variables but even then some care has to be taken to get accurate results.

Of course if you want a real laugh then watch the 'infomercials' on "Today Tonight" or "A Current Affair" on tv when they get on any automotive subject.

[brad]

Look at what VW managed to do with their emissions testing in a controlled environment..

I do see the point in doing it in a lab/rolling road but we don't live/drive our cars in a controlled environment so a real road test in a daily driver gives good enough information for me.

trying to compare fuel consumption using different fuels by driving in the suburbs / open road is like trying to compare cakes that have been cooked in different ovens.

eg: Do test 1 over a 4 week period in January & test 2 over a 4 week period in february & test 3 over a 4 week period in July. The differences in fuel consumption would be significant - esp the jan feb tests.