>>11128447A lot of newer regeneratively cooled engines just have a bell made of two parts, one being channels and the other being an outer jacket, and there are only two pipes, one inlet for cryogenic propellant to go in and the outlet to carry heated expanding propellant to the combustion chamber or a preburner. Having a web of external plumbing is dated because it's excess pipe where none is strictly speaking necessary. Newer engines like the AR-1, BE-4 and Raptor all have regenerative cooling and all have very minimalist plumbing, even the paper F-1b cuts out an enormous amount of engine complexity compared to the original F-1. RS-25's on the other hand are composed of an inner layer and outer layer which sandwich a huge bundle of welded together coolant pipes, excess weight where none is needed, and the plumbing that carries propellant into those pipes is more complex than necessary, yet more excess weight.