Good explanation of the balance shaft system NR
There's lot to it actually...
There are a lot of "forces" occurring in a reciprocating engine. Forces due to the energy from combustion AND inertial forces are the most predominant. At lower engine speeds the combustion force is more predominant however as the engine speeds increase so do the inertial forces that eventually overtake the forces of combustion.
Most 1st order inertial energy occurs along the cylinder axis, which is vertical in a 4cyl engine (peaking at TDC and BDC) and is offset by crankshaft counter-balancing, as well as careful balancing of all rotating and reciprocating masses, combined with torsional damping devices. (e.g. crankshaft vibration damper, flywheel etc)
However significant 2nd order vibrations actually occur LATTERALY in an 4 cylinder engine (all engines actually but lesser so in V engines) due to the extreme connecting rod angles formed by 180 degree crankshaft throw spacing (most predominant at 90 degrees after TDC). So certainly force on the piston due to combustion gets transmitted to the piston and then to the connecting rod, but due to the rod angle formed as the piston moves down to 1/2 bore, ever changing levels of LATERAL force gets transmitted from the piston to the cylinder wall and even to the crank main bearings.
This occurs TWICE every crankshaft revolution, once for each ignition event (hence second order) . So the rotating balance shaft system attempts to keep a counter-effecting mass, "in-phase+180 degrees" with these lateral forces. As engine speed increases this effect is diminished as inertial forces eventually overtake- so the balance shaft system becomes constantly less effective as engine speed increases.
Below are a couple of a pics of the balance shaft system used in the Ecotec.(*Full credit to General Motors Corp of course) Note how the shafts rotate in opposite directions and at twice the speed of the crankshaft SO the balance shaft counter weighting can be 180 degrees out of phase with these forces for BOTH cylinders that fire within each crankshaft rotation, in order to effectively cancel them out.
As far as removing them goes. This HAS been done on the engines that utilize dry sump oiling. However the galleries that feed the rear balance shaft bearings (more of a bushing) are somewhat difficult to plug. One method is to use the special tool used to remove and reinstall the bushing, and install a specially prepared bushing that effectively plugs the gallery passage. Merely turning the bushing is not really an option due to the way the factory bushing designed. It has an oiling channel so that the bearing does not need to be perfectly lined up during factory insulation. However it CAN be modified so this channel is not effective.
Testing at realistic RPM levels (<8000) has proven however that the use of simple GMPP "neutral" shaft assembly (i.e. perfectly balanced with reduced mass) is the most effective means of regaining the horsepower lost by rotating the stock counter balanced assembly. Electric water pumps require significant electrical current and add increased loads on the electrical system. So some of the perceived "gains" would be offset by additional belt loads on the generator.Plus for street, the "real-world" performance and reliability of the electrical pump and plumbing would need to be validated.
But IMO in a STREET engine, the gains provided by complete elimination of the shafts are not significant over and above the neutral shafts and are not worth the additional complexity and risk. However if the engine is expected to reach/exceed 10,000 RPM in a race-only application it still would be a very good idea. Remember at 10,000 crankshft RPM these shafts will be spinning at 20,000RPM! and it's doubtful that the entire stock chain drive mechanism has been validated to those speeds.
WopOnTour
