As some may know already, the factory grounds Subaru picked are very weak. This home-made kit will reinforce the grounds in the entire front part of the car and engine.

Total cost was just over $30, total build time was just over 30 minutes. For tools, you need a 10mm wrench and/or socket, a 12mm deep socket, allen wrenches for your distribution block, either some strong pliers or a hammer to connect the ring terminals, and some scissors or sire strippers. For the wires and stuff, you need about a foot and a half of speaker-quality 4ga wire, and 15-20 feet of speaker-quality 8ga wire. I got two feet of 4ga wire and twenty feet of 8ga wire to be on the safe side. I had just under a foot of 4ga wire left over, and a few feet of 8ga wire left over. You also need a 4ga into 8ga distribution block, one 4ga 1/4" ring terminal, two 8ga 1/4" ring terminals, and two 8ga 5/16" ring terminals. A few zip-ties come in handy, also.

First, disconnect the negative battery terminal, then onnect one end of the 4ga wire to the negative battery terminal via the 1/4" ring terminal, and the other end into the distribution block. Now take your 8ga wire and cut individual pieces to the appropriate length (one goes to driver side strut tower, one to driver side intake manifold, one to passenger side strut tower, and one to passenger side intake manifold).

Connect the 8ga wires to the distribution block, then route them to their locations. Connect two to the strut towers via 1/4" ring terminals, and two to the top side of the intake manifold via the 5/16" ring terminals.

Tighten everything up and zip-tie the wires in place. Done! I will say it's $30 well spent. My engine runs much smoother, idles better, and feels a little peppier. Before I made my grounding kit, then engine would stumble a little bit when the fans kicked on, now it doesn't. It would also stumble a little bit when accelerating with the a/c on, now it doesn't. Pulls smooth to redline.