I know I'm late, but this is fascinating.
And I had to relate it to car engines because I don't own a rocket.

You can make reductions to complex mechanical systems. No part is the best part, am I right? But there's almost no way to reduce THAT many parts of the system..I mean look at R1 compared to R3. 
How? And what allowed them to reduce the total mass by +50% and increase thrust by 30%? 

~Car Engine Simplified~
A metal block with combustion chambers (cylinder), pistons, connecting rods, and a crankshaft.

Process = 
1. Air + fuel mix in combustion chamber
2. A spark causes a small explosion
3. That explosion forces the piston down, turning the crankshaft
4. A spinning crankshaft becomes horsepower, spinning the wheels via a transmission (hence why cars have 2 HP ratings, wheel hp vs crank hp)

Result = Mechanical power (HP) moves the car.

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