Well, that depends on exactly what you want to accomplish. In my case, I wanted to use a 9" K&N filter and position it such that it drew in air from OUTSIDE the engine compartment, since the air under the hood gets quite hot during normal operation.
So, I bought a smooth pipe bent in the same way as the ribbed, flexible plastic pipe that went between the MAF and the throttlebody. It basically had the same inside diameter as orig. pipe, so a rubber 3" pipe joint adapter (found a local hardware store) connected MAF and smooth pipe with a couple of stainless steel clamps. Then, used another 3" rubber pipe joint piece in front of MAF to 3" PVC piping (hardware store again) to a 3" to 2" PVC adapter, to hook up the K&N. With some creativity, I was able to end up with the K&N positioned behind the front bumper, and in front of the driver's side fr. tire, sucking cold air from under the car. And, don't worry, it still drives OK in the rain.
I think a mod like this can give you a couple of tenths.