I just aint sure about my a4... i know it needs premium gas but my car's old owner always fill it up with regular gas... what the heck... what should i do? just stick with reg or prompt it to premium? more power?

Thanks

 

If you put things that are lower then the minimum requirement, the car will not like you.

 

use premium. you get higher mpg with higher octane levels anyway

 

and yes, you get more power. Higher octane number=more energy in the fuel, as it lets the engine run at a higher compression rate, delivering more power.

 

Higher octane fuel does not have more energy. It does allow for
more boost and ignition timing advance.

 

So true, it actually has slightly less "energy". What it is, is more thermally stable. So it doesn't pre-ignite & cause a ping. This allows for more boost (F/I cars) & timing advance. On non turbo cars, you can run higher compression & get more power.

The static compression ratio can never change. What I think you meant is you can run higher boost?

 

LOL! Classic

 

But a car can be designed (or maybe modded) with a higher compression ratio if the maker knows that they're going to require higher octane fuel.

 

my car says that it need premium but the minumum octane rating is 87, i assumed this is for europe, but for the short time i took 87 octane i notcied several thing, im pretty sure the car realized it was getting cheap gas and therfore retarded the timing, i had slightly less power, i would average about 250mile on a full tank with some spirited driving in a city enviornment. once i realized what i was doing, i seafoamed everything and started using premium ( always shell BTW) with that i feel more power espacially in the low RPMs and it pull alot better throughout the powerband, i know get about 300 miloe per tank with some spirited driving. all in all just use premium the 20 or cents you pay extra is really worth it.

 

the octane rating determines the burn rate (of the fuel)...

depending how your engine was designed it may need a specific octane rating for the fuel used.