Hi Rovert2d6
The higher you raise it, the higher the 'blow off' pressure will be for the safety valves. However, on many locomotives, you'll simply end up running at that higher pressure and end up blowing off in the end anyway. Well, sort of. It'll take you a while to reach this sort of pressure if working hard...
It will, however, also change the starting pressure of the loco to be much higher level. This will give you a much more powerful locomotive, which will mean that you'll need much heavier trains to make it behave even somewhat close to the prototype. It'll also make the locomotive more likely to slip, and possibly a lot harder to control.
Regards
