I just want to jot this down for the "folks playing along at home" that may have seen this topic 100 times but don't really have a basic understanding of the whats and whys.
The main reason for the tube in the pass galley (or alternatively bushing the individual lifter bores) is to guarantee priority oil from the pump discharge gets routed first all the mains...and at (more or less) equal pressure....Primarily in the event of a lifter leaving the bore due to valvetrain failiure. A "normally" functioning SBM oil system does the same thing under normal conditions but will deliver proportionally less oil volume due to the 8 parallel oil "leaks" occurring at each lifter bore.
The logic behind plugging the #1 Main lifter galley feed (regardless of whether you tube the pass galley) downstram of the main is to effectively cut in half the number of lifter bleeds ( from 16 lifters down to 8 volume drops) in the circuit that feeds the main bearings, again this ensures more "priority" oiling (volume and additional pressure) is available to the Main bearings. The bypass is exactly that, it bridges the gap between the left and right galleys once you plug the #1 main passage. If you do not plug or significantly restrict the #1 it doesn't really do much under normal running conditions. Plugging #1 also ensures all the oil to the #1 bearing has to leak through the bearing itself, not run to the path of least resistance (up the galley) at higher RPMs.
Enlarging the main passages from the galley increases the supply 'charge' of oil to the mains but does not necessarily increase the flow due mainly to the limits of the bearing orifice itself and at least partially design of the bearing shells (groove width, depth and surface area).
All are inter-related and a decent understanding of series and parallel circuit flow is really essential for understanding the cause and effect.
How much is adequate, how much is too much and how much is "overkill" I suppose what's being debated.
I wrote this quick so don't score me too harshly, lol
Not to be disrepectful, but tubing the oil gallery or bushing the lifters bore does not make it priority oiling. The oil still goes all the way up to the lifters and back down to the mains. Priority oiling will always oil the mains first.
That said, if you are not running a hydro lifter you should be blocking off ALL the oil to the lifters.
The only other exception to that rule is pushrod oiling. Then you need some oil at the lifters.
