I Have a 2004 Audi A3 2.0FSi sport. I cover about 25-30K miles a year mainly on the motorway. I have always just filled up with standard unleaded petrol as opposed to the dearer superunleaded 98RON petrol.

My question is should I really use the Super Unleaded or not. Does it really perform any better / give more MPG. Or is it just a waste of money unless you are a true driving enthusiast.

I currently get 40.7mpg which I think is really good.

Your advice would be appreciated.

Richard
Leeds, UK

 

Yes you should. The engine has to compensate for you using low octane gasoline by decreasing the timing. It can cause knocking in the engine as well.

 

I have a 2.0 FSI and in South Africa we only have standard unleaded. We have no choice as yet, but my car seems to perform 100%. Audi SA might have made some adjustments to compensate, but i doubt it.

 

modern (unmodified) cars like the A3 can run on standard fuel without a problem, like Jestnomen said...the computers compensates for it and it will cause no damage to the motor. you will however be losing some performance. i can't tell you how much but it is some. if you are simply commuting to and from work, stick with the cheap stuff. If however you want to go out and have some spirited driving put in the high oct.

 

your getting 40.7mpg. man. Wishes!!

 

If you don't use the High octane petrol then you will end up with probloms it will cause bad running. I havn't seen the A3 FSI have such a problom with it yet but I have seen an A2 run on cheap supermarket fuel that had terrible performace and was recterfied by just filling up with high octane fuel but it took 3 full tanks to get it back to proper running conditions. So my awnser is always use the high octane fuel before it dose cause a problom especialy with the FSI.

The way that the FSI works is it ignites the fuel with out a spark under compression like a desil, while you are driving at half throttle. While it is at idle or full acceleration it will use the spark to ignite the fuel (this is the basics)

 

Ummm not exactly. FSI just directly injects the fuel into the cylinders via very high pressure. There are still spark plugs.

 

Audiscientist - I don't intend to be rude, but someone has been telling you a bunch of crap. Most of what you said is simply not true...

FSI is not a compression combustion engine.

Using a lower octane fuel makes and engine vulnerable to Pre-detonation (knocking/pinging). Pre-Detonation means that the fuel in the combustion chamber is not ignited by the advancing flame from the spark plug but instead spontaneously explodes due to heat and compression (yes, like a diesel). Gas motors are not designed to operate in this fashion and it will damage the motor.

Basically Octane is a fuel stabilizer which allows the fuel/air mixture to be put under more pressure before it spontaneously combusts. Therefore higher octane allows one to use a higher compression ratio.

Modern automotive (Audi A3) engines have sensors that can detect knock and retarding the timing to prevent it, allowing engines to safely use petrol of lower octane ratings, with the consequence of reduced power and efficiency.