The Hull B having TR8s, while those engines are physically smaller than the Constellation's TR5s, would be ridiculous otherwise unless all ships are having their main engines changed to a new size system. So, are ships TR limited, or size limited? Can I put TR8s from a salvage operation on my Connie if they are structurally smaller than the current TR5s?asked by Grey Beard

So there's two aspects to that: One is that the TR rating is not a size rating. It doesn't say anything about how big the thruster is, it just describes how much thrust it can put out. The second part of that question is about taking a TR8 from a salvage operation that's smaller than potentially a TR5 that may go on a Constellation. In the specific case of that Constellation, I think that the thrust of a TR8 would probably shear off the engines from the Constellation, which is why the engineers limited it to only TR5s and not TR8s.