i believe its 2.5"
BUT ive heard that bypass valves rob any performance ur intake could have gained! but honestly man i was really concerned about hydro lock at first, but when i got the injen i really dont sweat it AT ALL its up super high from the ground where water could be, then the water that does splash up would hit your bottom splash shield under the engine bay.
the cone sits above the vents in the wheel well, so the water would not hit the cone, it would hit the intake piping. but for safety precautions i did cover up those vents and bought an injen hydro shield just in case! i dont worry about water at all! (but i would reccomend you do these 2 things, the hydroshield and cover up those vents)