I am sure I will be corrected if I am wrong, but the by pass valve is to deflect water coming into the intake, right? So, it really depends where your CAI gets installed. If it is open to the road, then I would go with a bypass valve or if you live in a very wet area. I have an AEM CAI on my car and it is protected from direct street and air because it is mounted in the wheel well above the left front tire. I suppose if I tried to plumb direct air into it I would consider the bypass valve. I was looking around and you can buy the bypass valve by itself and then cut your CAI and mount it in between the cut.