Thanks Chris.
I remember now that pressure is a measurement of resistance to flow regardless of volume being moved.
Volume is the capacity of the pump to move the liquid into the system. The volume of the pump is dependent upon the speed it is driven and of course the pump design.
Ron
The oil filter adapter I have on the engine does not have a GM bypass valve and depends on the bypass within the filter. Wondering if the bypass in the filter isn't opening (less resistance) and thus the loss of pressure when I hammer the throttle.

 

I think you have your answers now, if you really want a little better oil pressure hot go back to the 15-40W, you will probably pick up 5 PSI and call if good. There is nothing bad that will happen at 20 PSI hot idle. Time to enjoy your car and drive it more. It is ready to go.

 

Thanks Mark, I am easily confused and very much a tinkerer with these old cars. Even the 15# of pressure at hot idle and 30# at cruise did not worry me. It is trying to verify the drop in pressure is due to changing bearings with greater clearance is the challenge. I am at this point satisfied with the latest change. The operational characteristics of the T4 dino oil and the 10W30 full synthetic have to be part of the equation as the synthetic flows like water with little resistance.
I put synthetic Valvoline Restore and Protect 5W30 in the 350 +.030" in the 68RS for a comparison. It has 130K miles on it and was my re-camed drag racing engine. I have not yet paid enough attention to the oil gauge to see how it acts. I haven't kept track of the oil consumption, but I know it is less than a quart of consumption per 500 miles on T4. Might be time for an amazing Westlotorn rebuild.
I also tried Valvoline Restore and Protect 5W30 full synthetic in our 25 hp Kohler in the Cub Cadet with 900+ hours. It didn't like it and I had to top it off every time I mowed for an hour as it developed a leak at the front crankshaft seal. I went back to straight 30W dino oil and the front seal leakage has somewhat self healed. I may try a miracle additive of some type to soften the seal or end up with another rebuild.
Thanks for your continued sharing of your vast knowledge
Ron

 

Rebuilding without a bore and hone is only an option when you do not have wear in the cylinders or damage in the cylinders. Old engines running old cast iron faced rings wear the cylinders quite a bit. At 130,000 miles your 68 probably is due for a full rebuild not a freshen up. Modern engines like the LS even at 200,000 miles usually have perfect cylinders in them. I did not wish to guide you down the wrong path.

 

Indeed, the 350 may need a bore and pistons. The 010 block was bored .030" and new forged pistons installed many years ago. I used moly rings for the rebuild which may have helped, but 130K is a lot of miles even though most were interstate driving over 120 miles each way as a daily driver in the summer before it became a classic. At this point, a quart of oil in 500 or 600 miles does not warrant a rebuild and the plugs are not indicating significant oil usage nor is there oil smoke from the exhaust. It now only sees 2,000 more or less miles a year, thus 4 quarts of oil = ~$25 v.s. $1,200 +/- for a complete rebuild with new pistons, flat tappet cam, valves, and guides.
Can't get lucky twice!!! If it ain't broke rule.
Ron

 

If the pressure is dropping when you hammer it...it's getting into a windage or oil control issue or the pickup is too far away from bottom of the pan and getting uncovered. If there's oil over the pickup it typically won't drop. What pan is on it? Did new pump use the new larger 3/4" pickup tube?

JIM

 

Thanks Jim,
The oil pan is the original 4 quart pan (5 qts. with the filter). I used the rubber gasket and set the original 5/8" dia. pickup 3/8" off of the bottom of the pan. I though about that, but the drop in oil pressure is immediate upon acceleration. I didn't find any foaming in the oil. I think I'll add 1/2 quart of oil and see what happens.
Ron
Continued confusion: Drove the 68RS which has 4 quarts including filter of Valvoline 5W30 oil. I believe it has a high pressure pump as I built it for the street and strip. Not a HV pump. Here are the results:
​​​​​​Cold Idle 40# @ 1200+/-, Hot Idle 28# (30#), Cold cruise ~2000 RPM 60+/-, Hot cruise 55-60+/- (60#), Hot hard acceleration to ~ 4500 RPM 60-70# and climbing. No drop in pressure upon hard acceleration. The (**) is a second gauge, 100# gauge.
Seems to confirm the cavitation in R66 with the HV pump.