Q: i am going to buy a 1998 audi A4 with turbo, does that mean i need premium gas... do all cars that have turbo need premium gas
A: There is a fair chance that using lower RON ( Octane ) fuel will create pre-ignition ( Pinging , Detonation Etc ) in ANY vehicle that is specified to run on the Hi Octane fuels by the manufacturer. There WILL certainly be a loss of Power & Performance by using Low Octane fuel & a good chance of worse fuel economy. I personally would not risk using a lower grade of fuel . Are the fuel savings going to equal or better the cost of a possible engine replacement or rebuild due to the damage caused ?