As I know it should work. Re-download the mod from here: https://www.beamng.com/threads/super-high-speed-apc-btr-80.42261/ Also, you can go to https://www.beamng.com/threads/lost-beast.80897/#post-1349838 and install the realistic and slow version of the engine if you want
Are you using "btr-80-v22.zip"? the folder arrangement is "\btr-80-v22.zip\BTR80\" which is not correct. You need to create a vehicle folder between them like this "\btr-80-v22.zip\vehicles\BTR80\"