Oil pressure change w/ roller lifters in unbushed BB?

With those lifters in the picture you will experience low oil pressure at idle. The good news is that it doesn't cause any damage. I have done multiple inspections on big blocks with 15-20 lbs idle oil pressure with those lifters and the bearings looked new. I would still look into bushing the bores or a full body lifter at the right diameter. J.Rob

If there was such a thing as a full-body lifter w/ offset intake seats and EDM oiling of the bearings, that would be the hot setup. There may be something out there now that fits that description, but with my luck it's a $1000 set of lifters...

I don't need pushrod oiling, but the other features would fit my application better IF the cut-out band is (and this seems to be a point of contention) the reason for the difference in oil pressure.

Some builders say the cutout results in the lower oil pressure, while others have said that problem is a result of the lifter body not extending far enough down over the roller itself, thus exposing the oil gallery in the lifter bore to an open passage at peak lifter rise.

I'm looking at a cam w/ a .434" lobe lift, so that "should" still be in the safe range from what I recall discussing w/ Brian when I purchased the lifters.

This will be my first "roller rodeo", so I have to admit ignorance on the issue and am trying to be prepared for what may result.

I don't know if you have the original IMM lifters or the revised ones.
One was noticably taller than the other (2.25" compared to 1.78" in my picture of Comp 892)

FWIW, this is what I measured on Comp 892. No noticable problem with a 0.434" lobe lift. But I didn't idle the car much to observe it either. I do remember doing a check when putting them in the 400 block. The oil galley was nowhere near being exposed at max lift or the base circle.

FWIW, I put a cam in my unbushed 451 block and dropped all the IMM lifters in to try and determine whether that cam / lifter / block combination was exposing the lifter bore oil gallery openings at peak lobe lift. If my measurements are reasonably accurate (some of them are "eyeballed" by putting vernier down into the lifter bores, this particular parts combination appears to be leaving the bottom of the oil gallery passage covered by approx. .080" of lifter skirt... at least on the bore that I measured.

Knowing how much variance the old Chrysler castings have, I can see where this might be hit-or-miss on whether each lifter / bore combination manages to cover the oil gallery passage at all times, or allows a small opening as the lobe reaches peak lift.

As Brian @ IMM mentioned previously (older thread), he's suggested some of his customers to have cams ground on smaller diameter base circles to reduce the likelihood of this happening. I'd have to measure the base circle on this particular cam to get any reference # for comparison, and wouldn't know w/o other people providing additional measurements on whether what I have falls into the "big", "average" or "small" base circle.

For the people who have seen a reduction in oil pressure, is this only at apparent idle, or does it reduce the pressure across the entire RPM range? I figured if it's across the whole RPM range, running a stiffer oil pressure relief spring might help to band-aid the reduced pressure.

One of the many reason I am putting 1.7 ratio rockers on my 511 is the ability to use a smaller base circle cam.