What RON Fuel for re-map

[gezzerS4]

Question, does it matter what RON fuel you have in the tank when you have custom Remap, I can't make up my mind if having a lower Ron (95) when they do the map will yield better results when you put optimax or ultimate back in, or having the tank loaded with 98 will be better from the off.

It's probably a dumb question but any thoughts

[Paulm]

97/98 is the only way to go.

If you use 95 the tuner will advance the ignition / boost as far as he can on that fuel without getting knock. If you then go and put 97/98 in the ecu wont know that so no more advance can be had.

If you map it for 97/98 and then put in 95 the ecu will <beep> the ignition in relation to knock. best of both words.

I would suggest you always run 97/98 anyway. On saying that I work away and my wife runs the car on 95. When I come home i run it on 97

HTH

Paul

[JonnyX]

S4 should be 98 RON standard anyway....

[Dippy]

Of course it matters. As Paul states, the higher the octane, the more the ignition can be advanced without causing knocking. Advancing the ignition is one of the key factors in increasing engine torque, and counts more than increasing boost above a certain level.

Depending on the exact engine model, the ECU will <beep> the timing if knocking is detected. This allows 95 RON to be used, but with a loss of performance. The advantages of a higher octane fuel can only be obtained if the ECU map is designed to, and that means the fuel has to be there during the mapping.

As Jonny states, Audi AG used 98 RON when producing the standard ECU map for the S4. We get a loss in performance when we put 97 RON in, let alone 95.