ZCD2.7T

Dude - it's not even CLOSE to that simple in real life, and your conclusion is flawed as a result.

I'll leave it at that.

Huey52

I have an A5 4-banger (yes, I know this is the S4 forum, but I do have a StaSIS tune and therefore my prior input).

m444

No. No, No, more boost means more fuel unless you run more lean. This only affects the fuel usage, when engine is running above normal OEM boost levels. The timing cannot be advanced much for the 91 octane tune. For the 93 or 100 octane tune, the timing improvement on on power & gas mileage should be more noticeable.

helix139

More boost does mean more fuel, but to say that boost is the only thing affected by the tune is incorrect. When you're running below ~5500 RPMs where the bypass valve opens stock, you're not going to be making any extra boost and and the gains you get are going to be a result of timing advances (they are there, even on 91) and changes to the fuel mixture (leaning it out, etc.). As long as you're running below ~5500 where the extra boost comes into play from the bypass valve staying closed, you're going to see better economy all else equal. The aftermarket has the advantage of not having to worry about people filling up with 87 octane and not having to worry about emissions requirements, etc.

m444

That assumes there is more room (before detonation) to add timing using 91 octane fuel, on the Stasis 91 ECU tune, when boost is below the maximum OEM level. Not sure how much room this is to add to timing advance over stock.

helix139

I am guessing (but it's a guess. APR would have to confirm) there is some. Nearly all cars have SOME room to add timing when using at least 91 octane, even your higher end ones that are supposed to run on premium.