Adding a CAI can add power. However you need to do it right. Just moving the MAF to a larger tube won't work and lot's of people find it better to keep the stock intake snake assembly rather than making their own just because they don't have a way to tune the AFR.
This adaptor mounts the MAF in the exact same way as stock making it read the exact same value. The open airfilter and less restrictive intake will up the air flow without changing the MAF calibration.
The MAF modded one is without vanes and are supposed to be mated with Yellow Celica injectors 310cc. This to trick the car to advance timing still with enough fuel. NOT teste by me but feel free to use it.
The adapter fits a 3" tubing