Originally Posted by grimlock
It makes it far more complicated than it is worth it, especially given the ground assumption that inherent differences are very, very small, say in the 1% range.
It's more logical for BMW to fit different turbos and cooling (as mentioned b4) so that increasing the output of the 20i without changing these components is not recommended.
Probably less than 1/20 20i's sold will be chipped so BMW would just let these guys have the free lunch that only costs them what 4-5k USD and they don't have to mess around with different components to spite the knowledgeable DIYer.
As mentioned before, the high compression version have different pistons but the low compression version is identical (again confirmed by ETK & BMW China technical rep). So how do they choose between identical engines to be a 20i & a 28i (talking abt low compression version only)? Randomly? Or is it better to use defective ones or underperforming ones (for a 28i) & detune it to be in-spec for a 20i? How complicated can that be when the defective rates are low?