Earlier combustion pushes back against piston coming up (counter productive) This is the reason why new engines combustion chambers burn faster than their ancestors. 302 head was an early example.
It also indicates that the mixture is lean at time of ignition. There's a difference between quantity and quality of mixture but when the engine is viewed as an "Air Pump"
that discussion is pointless here. Its easier to just change parts and discuss what part is better and why than to actually think about what the part actually changed in the engine.
