>>14185807>>14185834>>14185849A single main combustion chamber and nozzle is lighter for the same turbopump machinery. Larger chambers become difficult because of combustion instability, BUT, if you can tune the engine to not produce combustion instability, you ARE better off using a single nozzle.
Meanwhile, engine scaling has more tradeoffs than combustion instability. Larger engines are easier to cool because they have proportionally less material in contact with hot exhaust gasses per unit propellant flow rate. Thrust to weight ratio trends up as you scale up from a small engine, but then starts to trend down again for really big engines. The ideal real world engine is big enough that cooling is practical and TWR is high, without being so big that combustion instabilities are an issue. Of course, the actual size of engine you want is determined by your vehicle application. You could put a 6000 kN monster staged combustion engine on a propulsive landing booster, but that booster is going to need to be fuckoff large in order to land on that huge amount of thrust, etc
