No, invar boilers produce 32 steam/t, so 3 of them produce 96 steam/t, exactly the upper limit of the bronze engine. Anyway, the tin engine is at the red but hasn’t stopped yet. It’s less efficient than the bronze one and requires one extra invar boiler, so I’ll check which setup is faster.
EDIT: alright, the 3 boilers + tin alloy engine setup is faster, about x1.3 the speed of the other, which is what I was expecting. Since I want to burn more coal to get dark ashes faster I’m going to build that in my world