No question about it BUT have you tried driving the car on 87 versus 91 ? I had a Volvo V70 T5 and the first time I stepped on it I knew my wife had put in 87. It hesitated and was generally gutless relative to what it was with the recommended octane level of fuel ... gas consumption may be equal but performance is drastically affected so why bother saving $2.50 on a fillup and have a car that drives like an anemic POS ?

If you chip then forget about using improper fuel as you'll have knocking and ultimately do harm to your engine if you push it.

 

By burn i mean ignite just to clarify that. The higher the octane the less its effected by compression and heat. However it is true that the system will try to adjust the timing and you will loose a lot of performance. In the long run the difference is about 5 bucks per fill up (quick math with absolutely no though on numbers) which will be used up due to the fuel not being economically used by the car.

It makes no sense to go against something that was engineered and developed for years and complain why **** knocks or breaks after.
Always follow what the manual says, its there for a reason.

Hah funny though, soon people will start fuelling up with 87 and use octane booster and think they get the same performance and use cooking oil to dilute synthetic to save a bit of cash in the short run lmao

Its fuels 101 bro *Fist pumps*

 

If you want to run 87, on a stock 2.0T, it will be fine.

You will lose performace and gas mileage will depend on your driving style. If you putt around like an 85 year old grandma, you might even see an increase of 1-2 mpg's, but if you drive it even a little "spirited" you will see a drop.

The only way to tell if it's good for you or not is to actually run a few tanks and see what happens.

 

So what is recommended on an 04 A4 1.8t?

 

It should say right on the fuel door, but 91 Oct.

 

Usually the price difference between 87 and 91 octane is 10 cents. On a 70-80L gas tank the fillup cost is higher by $7-8. It is worth !!!

 

Just remember that the minimum octane in europe is 95. The engines are built with that spec in mind.

 

They use different octane scale. so thats not exactly true. I cant remember the scale or the names but in europe 98 octane ( i think) = north american 91. The octane number is is set by the oil company and as i said the one in europe uses different scale but its exact same in the end.

 

Here ya go: Octane rating - Wikipedia, the free encyclopedia

 

I bought my first '98 A4 1.8t last year. First month or so I used 91, like it says on the gas cap door. Then, switched to octane 87, thinking that all octane level gas is the same. After about my second fill up with 87, the car started pinging really bad. Performance was also affected. Never used 87 after that. Always 91.