I used to use a 1/4 inch think plastic box I fabri-cobbled together, and it worked great. I only gained ~10 degrees above ambient, the only downside is it wasn’t very sturdy, and didn’t look great, so I bought the Cobb box to solve those problems.
The box looks great for starters. The finish is consistent, and I love the little Cobb plaque and the Cobb branded plastic washers, just killer.
The fitment on an 09 wrx is fine, but a bit lackluster. I could only position the intake/MAF pipe portion slightly too far away from the engine with the MAF inside the box, or rammed super far in toward the engine with the MAF outside the box… I ended up going with the former but neither was an easy setup…. Also the screw all the way toward the front left is very difficult to get to, as it’s covered by the intake snorkel thing. Which wouldn’t be an issue, except you have to install the intake snorkel thing before the lid, otherwise it won’t fit properly… you can get to it, but it’s annoying…
Lastly, the heat rejection isn’t great, my shotty DIY solution did a better job, with the new box averaging significantly hotter than the old one… and that was after wrapping the outside in heat wrap and sealing all the edges with rubber edge guard trim (which they need to send dramatically more of btw)… This is likely caused by two issues. First is thickness, as the thin metal transfers heat really quickly, and the second is edge protection. There’s a lot of excess space on top of where the intake…
