Hello!
I've just been looking into this engine issue and pretty much figured out how to h4><><0|2 motor city files. Apparently, this version does not contain any engine stronger than 48HP so its not actually a bug, but lack of content(presuming that there are more engines in the german version).
If anyone has a PC copy of Oldtimer, and it contains more engines, I believe I could make a patch that would transfer these to the english version. All I would need is the 'game.stc' file, or its equivalent in Oldtimer.
Cheers!
Edit: I've tested it out...
There! I managed to add an entirely new engine to the game. The engine issue can be adressed by transfering the data from the german version, or by creating a mod that would add additional engines to the game. I've pretty much figured out how (not that complicated, all you need is a hex editor), now its just the data.