Actually a 4" will fit just fine if you tighten down the clamp....
Trust me, I bought materials to make my own PVC intake and in my haste (Home Depot was closing) I bought a 3-3 coupler instead of a 3-4 coupler. Combine that with breaking the stock air box getting it out (long story) I now have the Spectre cone filter directly on the throttle body. It's not hurting anything but I have it on the 4" ring, I'm sure if I cut slits in the 3.5" one it would've fit but it was entirely too cold and dark for me to **** around with it anymore.
