HI djbalkanac,
we do not see any introduction of you...:
introduce-yourselfIt is not that simple, you can not tune +-%, it does not work that way.
You have to understand the whole system and every calculation or change.
You have to check every engine part for every engine (engine code is the main info to look for engine parts).
Etc. you have to check the turbo specification at which pressures can it run without the risk to damage it...
High pressure pump
Injectors
Fuel tank pump flow / pressure if there is one...
and so on...
You have to know what air / fuel ratio you can use without smoke.
I suggest you reed some basics on the forum, there is some good material about that.
Air is the main thing from air you can calculate the lambda you want to drive - how much more fuel you can inject.
You can have two same engines and each of them will achieve pretty different results.
Than you choose the first car you want to do, post the original file and than the fun begins. ;)