| So my friend has a '98 M3 auto 4dr.
Hes going to be buying a 3.91 differential and a dinan tranny chip. He currently does not have an engine ECU. My uncle, who is very knoweldgable about BMWs, says that it will work, but it just won't be able to be used to its fullest. Meaning, the car will shift higher, but the engine won't be optimized to the new tranny shift points... can anybody further explain this more clearly? | 
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