How to unlock FPS in Batman: Arkham Asylum and make the game smoother

(First, you need to log into the game at least once)

1). Navigate to the settings folder at the following path:
C:\Users\*YOUR USERNAME*\Documents\Square Enix\Batman Arkham Asylum GOTY\BmGame\Config

2). Look for a file named BmEngine.ini

3). Open it using Notepad

4). Find the category [Engine.GameEngine]
(To search for text in Notepad, press Ctrl+F (or go to Edit > Find))

5). Change the parameters within it to match the ones below:

• bSmoothFrameRate=TRUE
  
• MinSmoothedFrameRate=0
  
• MaxSmoothedFrameRate=280

~For MaxSmoothedFrameRate=280, ideally, replace the number with your monitor's refresh rate (in Hz); here, my 280 Hz is used as an example.~

6). Don't forget to save the changes for them to take effect
(To save the changes press Ctrl + S (or go to File > Save))
After saving, you can close Notepad

7). Open the properties of modified file and check the "Read-only" box to prevent the game from automatically altering the settings we've configured.

8). Now, navigate to the game's root installation folder and go to:
...\Batman Arkham Asylum GOTY\BmGame\Config
Open the second BmEngine.ini file located there and repeat steps 3-7.

For anyone planning to play the full Batman trilogy, these guides may be useful
https://steamcommunity.com/sharedfiles/filedetails/?id=3580726217
https://steamcommunity.com/sharedfiles/filedetails/?id=3581556923

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