Just a little video to prove a point. Some say you can go too large on a maf and drivability will suffer. We have always said, the more the merrier with a properly designed maf. Here is a video of our 141mm RMAF installed on a stock 2013 Mustang GT. No tune, nothing. Only mufflers. This was...
No you would not need a re-tune. Our no tune maf has the exact same transfer function as the OEM. maf and airbox.
If you bought the tune required kit, you would only need to change the maf transfer function in the tune.