if i change my Chevy air tube from 3.5" to 4" will i need to recalibrate
my MAF sensor ? my MAF is in the air box ahead of the tube.
or should i just buy a GM factory MAF from a 4" air box setup ?

 

Yes, the engine still consumes the same amount of air, the larger tube makes that amount of air move slower which should lower the maf hz for a given airflow. Example, you currently idle in the 2800hz cell of the maf curve you would move down into the 2300hz cell because the airflow is slower. Imo, you wont gain any performance adding a 1/2" to a 2.5' piece of tubing.

 

I will also be changing my TB from 87mm to 90mm. that's why i am
going to a 4" tube.