Portal 2 Tweaks outlined in this article will help you optimize the game to run with max performance and better graphics.
Portal 2 Performance Tweaks
Where to Find Your Config File
Instead of editing the default config, you can create a custom ‘autoexec.cfg’ and add your custom commands in it. Source Engine on start up looks for autexec.cfg so it would load the custom cfg if it finds in the specified folder.
For detailed instructions on all the Source Engine Performance Cvars, you can go through Tweak Guide here. Koroush has outlined all the source engine command along with the newer commands have considerable performance impact.
Portal 2 Gameplay Tweaks
Turns off portals pulling you towards them. Note. It doesn’t effect props. You can use:
to turn it off for props.
Turns off seeing portals through walls. Note. You will need to enable cheats before you can use that. Type sv_cheats 1 to enable cheats in Portal 2.
To disable hints at the beginning of the game.
Place portals on moving surfaces.
Portal 2 Graphics Tweaks
Creates a dynamic light at the spot you create portal.
Improves the quality of specular highlights.
Forces max texture quality.
Improves water reflections to reflect everything.
-window 1 -noborder
You can add it in the launch options to put the game in windowed mode without borders around the video.
Disables the intro video, also launch options only tweak.
If you know any other useful tweak, let me know in comments and I will add it up. You can also refer to our Portal 2 Troubleshooting Guide to resolve all the issues you can across while playing the game and try other performance fixes.