There is an awful lot of stuff in the engine compartment, that really doesn't need to be there, so to start things off I relocated the battery to the trunk. A full procedure for that can be found here in this technical article: Battery Relocation
The next thing to go and be moved to the trunk was the windshield washer fluid reservoir bottle. At the same time you can reroute the wiring harness to be hidden near the front rad support using tie-wraps. The exact procedure for the washer bottle is outlined in the tech article: Washer bottle relocation.
Now, with those two bits moved into the trunk, there's a number of things that can be tossed in the bin, if you like. Starting with the charcoal canister, the complete guide for removal can be found here: Charcoal canister removal.
|HICAS solenoids and lines|
|Green cleaned passenger side|
|Green clean drivers' side|
If you're going to be using an after-market boost controller, you can also plug the OEM boost solenoids' vacuum lines, and toss that in the bin as well.
You can also relocate the resistor pack for the fuel injectors to a place where it won't be seen if you like, and continue to tuck as much of the wiring away as you feel necessary, some of the wiring near the fuse box can really be cleaned up well. At the very least, re-wrapping the wiring with fresh electrical tape will help to tidy up the overall condition. I re-taped everything I could, including the ignition harness.
The last thing I did was to replace the coolant overflow tank with an alloy tank.