Air intake diameter ?

[Ghost10]

I’m going to change out the air box, but leave stock intake chamber box and add a shirt tube with a MAF but need to know the diameter of the tube for the stock intake where it attached to the stock intake box.

 

[Ghost10]

The reason for this is with a stock intake setup my exhaust with a racebullet, no 3rd cat sounds way better with an actual open air intake filter. I recently had a cheap eBay $89 intake setup but the shield was missing parts and the cone filter was too long and would need to cut inside fender lol f all that noise. So I’m thinking either run the MIT tube and a shield and cone filter or stock intake with cone filter

 

[Thrust]

The opening to the stock airbox looks to be 4" dia.