Smooth is right. Out the back, probably tap right into the throttle house, use that same diameter all the way back. You could possibly use some rubber tubing instead of PVC, like what you could get on a truck intake. I don't know where you could get it though. But that would be the only way to do it, unless you were to cut a hole in the seat. You're filter would have to go on the end of it. The only other way would be to cut a hold in the back of the air box, and run PVC out from there, but you would need to get another cover that is definately air tight.