For Constelation Class, why would they put 4 warp nescele (or whatever it is) when the performance not even better than the 2 warp Nes... errr Engine starship like Constitution.
They didn't just make the standard connie refit primary hull thicker. You can see where the connie disc ends and then there's more diameter still, and the two deck thickness at the outer disc is now what? Five or six deck worth of thickness.
The constellation with no secondary hull is still much more massive than a connie with
it's secondary hull, so twice as many engines.