AMX69PHATTY wroteLike most things there are both yes and no opinions on the need for the oil line mod.
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You can imagine how much oil is gonna squirt out of 1/4" at 40 PSI
and the oil volume that squeezes out from around all the bearings cant be that much.
The bearing fits are the restriction in the oil system that create the pressure.
And ya know AMC motors have ran more than 100,000 miles without one.
Good question though, I haven't seen a good answer to it either.
I'll give you my best reasoning for my "not needed" opinion.
1) The secondary feed paths from the lifter gallery to the crank bearings are smaller and therefore more restrictive than the lifter gallery - so adding a second feed path from the front to the rear of the lifter gallery will not increase flow to the bearings.
2) As stated above, it is the restriction through the bearings for a given flow rate from the pump that determine system pressure. For a given size of restriction the only way to increase flow through it is to increase pressure.
3) If there is any pressure in the system at all, flow rate from the pump must be in excess of the leakage rate through the bearings and valvetrain. To suggest that pressure decreases as you move downstream from the pump is to suggest that the bearings and valvetrain are able to pull oil from the feed paths in excess of the flow rate of the pump, and that cannot be the case if pressure exists. This is not a free stream system like a river with open capillary branches - at least not until the oil has left the bearings and valvetrain and begins to gravity flow back to the pan - it is a closed pressure system up until the oil has passed through the restrictions at the end.
4) If pressure exists it must be equal from one end of the system to the other. If it is not equal at both ends of the lifter gallery there must be a blockage. If there is a blockage in the lifter gallery that is more restrictive than the feed paths to the bearings you have bigger problems that need fixing.
5) Pressure measurements taken at both ends of the lifter gallery during dyno testing show no measurable drop in pressure from one end to the other. The valley bypass line is in effect tied back to the same feed source at both ends and therefore must have equal pressure at both ends. A line with equal pressure at both ends will flow nothing. The lifter gallery bypass line is therefore of no use.
6) Extended high rpm operation has been known to deplete the oil capacity in the pan by pumping all the oil up top before it can drain back down, resulting in the unporting of the pan pickup and subsequent system pressure loss. Higher capacity pans, improved drainback, and smaller ID pushrods to slow the flow of oil to the top are probably the best solution to this problem.
7) In my opinion the only oiling mod a common lower rpm jeep motor may benefit from, aside from a properly functioning pump and clean system, is a larger capacity pan with either baffles or a swinging pickup to help feed the pump during operation in unusual (high angle) attitudes (more unusual than my own).
