Assuming the record breaking steam cars were fitted with traditional governers, were there any banked corners that they could get a sufficient speed up to that the governers no longer worked and the boilers were at potential risk of explosion?
Or did the governers have sufficient tolerance built in?
Not really sure what you mean by tolerance. But in general, governors govern speed, so if the car is going faster than the governor setting, the governor will stop allowing steam to enter the power pistons and futher increase the speed of the car. That should not change the possibility of a boiler explosion, though, if the boiler is designed properly (that is, with a safety release valve).
I’m not sure exactly what situation you’re concerned about here. Let’s say that the car is going downhill, immediately after getting the boiler up to maximum operating pressure, like what you might see on a long climb. The car tops the crest of the hill, then quickly gets up to maximum governor speed on its way down again. The boiler is at high pressure, but the governor is keeping any steam from getting into the piston. If the pressure keeps building, the safety valve will go off at a given point and release the excess pressure, keeping the boiler from exploding.
The other scenario is that the car is travling around a high-speed track with high banked corners. If the car gets going so fast that it is at a 90 degree angle to the flat ground, then any water inside the boiler could now be at a level that covers the safety valve. Again, let’s say the car is at maximum governor speed, and no steam is getting to the piston, even though the pressure continues to build. The safety valve should still open if the pressure inside reaches the safety set point. The safety valve doesn’t care whether it’s steam or water inside - it just “knows” how much pressure is against it and will open.
It should be OK, but let me know if you’re going to be driving around here anytime soon.