I want to switch from the Greddy Airinx to a K&N filter before I install my rebuilt turbo, but my car is 100miles away and I can't measure the size of the MAF peice. I'm guessing its around 2.5", but I won't have a chance to actually measure it until I go to reinstall the turbo. Does anyone know this off the top of their head?

Try PMing PURNRG. I'm pretty sure he has a K&N filter.

It's actually 3".