The UF1s engine seems quite small for a 4 cylinder engine, and many cars like it have 3 cylinder engines. Also it would make the UF1 more desirable being the only 3 cylinder car in LFS.

I was wondering the same a few days ago while I was having some fun tuning some cars with a tweaking program.
If we check some source though it's real counterpart had 4 cylinders as well: https://www.ultimatespecs.com/car-specs/Austin/376/Austin-Mini-1000.html
I just realized the hp and torque are much higher in LFS.

The synthetic sounds of LFS scale to the right number of cylinders so I made a bi-cylinder 1L to show it to a friend and he was amazed that the game was producing a bi-cylinders dynamic sound straight-up. It would be great to make these tweaks inside the game itself when not playing in multiplayer.