I just ordered an Injen replacement filter (1018-BR) and it seems to be smaller than the filter I ordered for it a few years ago. The inside diameter is a few 16ths off, and it is shorter than my other filter. The ID is small enough I had to take a screwdriver to pry the lip up and slide it around the MAF adapter to get it to slide on.

Just wondered if they changed the design...

 

Yes they did. AMS Oil began making them for Injen I believe and the design changed slightly.

 

Well damn, that sucks. The design is enough off that it's a PITA to install it.