Why do you need to remap your engine after turbo installation ?

While the correct amount of fuel is automaticaly correct with the original afr table ?

Joan,

I'll simplify, but one example of how this occurs is related to the flow of the exhaust housing. If it's less restrictive, that reduces exhaust pressure. This improves engine VE because exhaust can more easily exit the engine and pass through the exhaust system.

If your calibration doesn't account for a change in exhaust pressure, via modeled or sensor based exhaust pressure, you end up accounting for this change in the VE or main fuel table.