I will be installing a 85mm maf on the car and was wondering when I take it to get tuned what exactly is changed from the original 75mm? I would just like to understand the process, thanks.

 

It's just a calibration setting. GM MAFs use a Hz frequency (0 to 12000 Hz) to tell the ECM how much air is going to the engine. With a different MAF, all that changes are the values associated with each frequency. Sorry I don't have a screenshot of my tune file. I'm sure one someone else can show you a screenshot of a MAF Airflow vs. Output Frequency table.