Air Box Mod
I did this mod and lost about 3 miles a gallon. Hollowing out the box allows it to get to hot creating the air intake temperature to rise. The single layer of plastic just isn't thick enough to absorb the engine heat. Do not do this mod if you are trying to save gas mileage. Same situation if you remove the air box completly. Done both of them and don't recommend either one.
I went a bought a Volant CAI and got my 3 miles a gallon back + 2 more. Best way to go even though they can get pricey..