bushing lifter bores on 340
IMO, the big issue you face with a pushrod-oiled top end and restricted lifter bores is the need to get oil up the pushrod. You need an oil path to do that...so if you drill a small hole, you should consider the placement of the hole as important as the size.
This is compounded by a hydraulic lifter's need for oil, if you are running hydraulic lifters (which is never a good idea unless you are a 68 year old woman named Agnes).
What I'm saying is....a small hole (like .046") is a good thing, but not if you keep it covered by the lifter body at all times. It needs to align with the lifter's oil hole at some point in time.
The factory 'hole' in the lifter galley is huge - not just in terms of oil flow but also in meaning that it helps ensure the oil hole in the lifter will be fed oil. It's also pretty forgiving when different lifters are used...various lifters usually have their oil holes in different locations along the lifter body.
So....you should drill the hole small but you should also have the lifters you plan to use 'in hand'....with the cam installed, drop them in the bore and measure where the hole sits then use that to position your lifter bushing hole.
I drilled mine at/around .046" but I first dropped the hole (using a 1/8" end mill) 1/8" down. This gives the .046" drill bit a flat surface to start against, and it also gives a much bigger 'landing zone' for the oil holes to align. In other words, the holes is flowing .046" but the lifter 'sees' a .125" hole which makes the alignment more forgiving.
See pic:
View attachment 1715583720View attachment 1715583720
This is compounded by a hydraulic lifter's need for oil, if you are running hydraulic lifters (which is never a good idea unless you are a 68 year old woman named Agnes).
What I'm saying is....a small hole (like .046") is a good thing, but not if you keep it covered by the lifter body at all times. It needs to align with the lifter's oil hole at some point in time.
The factory 'hole' in the lifter galley is huge - not just in terms of oil flow but also in meaning that it helps ensure the oil hole in the lifter will be fed oil. It's also pretty forgiving when different lifters are used...various lifters usually have their oil holes in different locations along the lifter body.
So....you should drill the hole small but you should also have the lifters you plan to use 'in hand'....with the cam installed, drop them in the bore and measure where the hole sits then use that to position your lifter bushing hole.
I drilled mine at/around .046" but I first dropped the hole (using a 1/8" end mill) 1/8" down. This gives the .046" drill bit a flat surface to start against, and it also gives a much bigger 'landing zone' for the oil holes to align. In other words, the holes is flowing .046" but the lifter 'sees' a .125" hole which makes the alignment more forgiving.
See pic:
View attachment 1715583720View attachment 1715583720