Originally Posted by Lotus99
So why are the flash tuners running so rich?
Because the closer to 14.7 you get the more unstable the combustion is...the combustion time is fastest at 14.7 thus leaving little error for timing variance.
Ideally you would want the combustion to start a split second before the piston reaches apex on the compression stroke and reach full combustion a split second after the apex of the piston (transition from compression stroke to power stroke)
When you move away from 14.7 your combustion time lengthens which facilitates a larger amount of allowable error at the expense of power because the peak of the power produced by the combustion comes further after the apex of the piston depending on your timing setting.
When flash tunes are dealing with the BMW computer, which is finely tuned from the factory for the factory settings, they want a large margin of error in higher RPM's especially when they are ramping up the boost because they are taking timing and boost pressure into their own hands.
You will notice that piggyback tunes have near identical A/F's to stock because they are simply altering inputs to the computer algorithm, but the stock software is still operating under the same tolerances.