i dont know about emissions
but FE I can comment about.
all numbers with AC on max and blower on 2
if driven normally, stock VDI gives 18.2 kmpl
after the filter and box i get 19kmpl- not a big difference.
if driven with the mods in place, specifically for mileage- i get 22kmpl
if driven with a heavy foot in race mode- 14.8kmpl
Note- after the tuning box- the car is in race mode all the time

cant help it.
I slow down only when family is with me.
FE after the tuning box is very,very sensitive to driving style.
but the object of the tuning box is not mileage, its fun, and driveability
AFAIK- the amount of fuel injected at lower revs is altered only by a very miniscule amount. but it is injected over a slightly longer period of time.(Jomz or sameel might be able to educate us here)
this gives higher torque at lower RPMs, which explains the significant increase in FE at lower RPMs