4Game

TLDR: you still don't need the filter installed, or you can install and turn off the gas.
So I've been seeing posts recently people still asking about how bugged the air filter unit it. Some people answer and others wondered if they fixed it but didn't tell anyone. I've done my testing and here's the numbers I got. From doing one full sprint for strength and endurance.
Start strength: 58.8
Start endurance:70.9
Build complete, not installed:62.8/74.9
Installed the build, no gas:62.8/74.8
Installed the build, gas on:64.8/76.6
Installed the build, with the filter:64.7/76.6
Installed build, with filter, no gas:64.8/76.6
Some small difference because maybe I hit a wall or did an extra footstep in walking.
I then decided to max out endurance numbers to a 0 percent to see how much distance it took, got to 84.4 still 1 percent gain and the timer ran out for factory, traveling 3.362 km (one sprint bar was for strength though)
And did the same for strength 71.8 and traveled 2.599 km (got bored) I'm not sure but maybe the more weight you carry could level it faster too.