I know that we only put old MAF sensor to new bigger 74mm MAF housing.
Normaly old MAF sensor is designed to 68mm diameter. Physically fit to bigger 74mm. But if we put it to 74mm diameter I think that he give not correct infos to ECU.
I not know how explain it. ECU not know that we change diameter. Old MAF sensor/ECU think that measure air flow in 68mm all the time.