Everytime you open a crate and get disappointed because you got no tuning parts or even two barn maps? Now read this:

Step 1: Save your game by clicking the right mouse button -> save game or Esc->save and go to main menu and load your save again.
Step 2: Open the crate and see what you got.
Step 3: If you doesn't get any good parts then press the right mouse button -> settings -> load game (which loads the last savepoint of Step 1).
Step 4: After loading you repeat step 1 - step 3.
Step 5: When you got good parts then press the right mouse button -> Settings -> save game and open your next crate.

I recommend to open just one crate even if you have multiple ones in your inventory. The reason for this is simply that you would waste crates and have a high risk to got perfect parts in crate #1 but in crate #2 you got 2 barn maps and a normal part. And believe me, i got multiple times 2 barn maps out of crates.

Depending on your system power and the number of mods that you're using this shouldn't take more then 1 minute. Also look for tuning parts with higher +quality because every +quality step gives the part 10% more power increase. For example a +4 quality turbo charger. A normal charger out of the tuning shop will have +10% of power increase, the +4 Turbo charger comes with +14%.