I have 80psi cold (adjustable regulator, turned in 2 full turns), 15psi hot idle at 500rpm in gear. When on the highway, I'm about 3krpm. I'll have 50-60psi, but if I get on it the oil pressure goes down to about 40, but if I let off it swings back up to 50-60. The numbers dont bother me, it's the lowering of the number with increasing throttle that concerns me. Only does it on the highway, nowhere else. is it an rpm issue? oil filter? oil level (its full) going down too much due to extended high rpm?
That's not normal. You may be emptying the pan, have a partial blockage of the pickup, or the oil is going away from the pick up.
the only thing that makes sense to me is that i may be sucking tons of oil up top and nearly emptying the pan. these engines arent made to be at 3k rpm for minutes let alone hours on end.
Oh yes they are. I've heard of hi volume pumps emptying the pan when drain back is insufficient. You have a problem if your readings are accurate. Take the valve covers off and make sure the drain back holes are open. Saw one guy who changed his valve cover gaskets, and didn't clean out the gasket material he scraped off the heads. It clogged the drain back holes.
can confirm the drain holes are clear. i had the engine out recently for headgasket replacement, its got 10k miles on a home rebuild. there was pitting on the coolant port surface of the block where the gasket blew out.
Temporarily add an extra qt of oil to your engine, then go repeat the driving conditions. If this improves your pressure fluctuation issue you'll have a direction to look into(volume and return). If not look elsewhere. Is your oil pan dented on the bottom. Pickup tube or screen obstruction limiting amount of oil that can travel through it? Remember to remove the extra qt of oil
Also consider oil aeration and oil turning foamy. Engine Masters on the Motor Trend Network did a show on just that thing. Oil pressure dropping at higher vs mid range rpm
I go with adding the extra qt and see if this cures the problem. I have the high volume oil pump large gears and all that but also have good oil mods done. I have 50-55 at 3 grand on the highway and if I floor it the oil pressure will go up higher to 70 at top end of 6 grand. maybe once you are on the throttle can the seal in the rear crank leak out from the extra pressure put on the crank and rods when floored? I do not know if this is possible or not. Possibly the screen in the pan is semi plugged and not getting full flow. I just can't see oil getting pumped to the top and not getting back in the pan in time. When the engine is floored there is more pressure on the front cam and the bearing this could be where the oil pressure loss is happening. Was the front cam bearing changed or anything like that? Adjust the regulator so you have the 45 lbs at 2500 rpm as the factory manual states and see if that makes a difference. Back off the screw to see if the pump starts to regulate correctly. you may have the thing screwed in too far it could be bypassing the filter and causing a pressure drop. Try a different brand of oil and see if this is the problem and use a Wix filter.
I have had the EXACT same issue for a few years, even on my old build with the cross drilled crank, AND stock pump. On this build with my spare crank (NOT cross drilled) Molnar rods, all clearances good, and my original 1971 block, roller cam, lifters, TA rockers, and TA cover, it STILL does the same thing, on the highway for awhile yah give it throttle and oil pressure drops a few pounds, back off and it recovers. At the track, from a start it goes up to 65 or a bit more and holds there for the duration of the run My theory is on the highway the crank gets the oil aeriated and the pressure drops some, then give it throttle and it goes down even more cause the pump is pumping aeriated oil When you return to city driving or stop, the bubbles dissipate, all is normal again Try this, after a decent run on the highway and its doing this, find a stretch of road you can floor it up to 60 or 80 mph, see what the pressure does and report back
Maybe the 350 has a bigger problem with windage. Mark, didn't you change your oil pan? What if you run the oil a quart low?
Haven't changed the pan yet, general opinion is its a PAIN Im going to wait till I pull the engine for my aluminum heads install. I "think" the 350 does have a bigger problem with windage verses the 455, Im not sure if it has to do with the deep skirt or "Y" block design, or the fact that its pretty crowded in the block, with the crank being so close to the cam and all. While working on the wifes Tahoe 5.3, I noticed a full length louvered windage tray, and the LS block is similar to the Buick 350 (deep skirt) On Engine Masters, they had an episode regarding this oil pressure drop with increasing rpm, they used different pans, changed oil levels, and eventually got it minimized at upper rpm, but not eliminated
With stock pan, stock pump gears, ac filter, no ta regulator, no problems. 65lbs with no drop. I am going to try the ta allen bolt in the pump spring trick to add 5lbs more.
I have one of Steve Reynolds' pans on my 470. The instructions that came with it said to start with 7 quarts and watch the oil pressure for fluctuations. I have the TA Performance dip stick and tube assembly. 7 quarts brings it up to the "ADD" line on the dip stick. 8 quarts brings it to the full Line. I have always run 7 quarts, that is plenty of oil for me.
Did you enlarge the suction galley? That's where I'd look, plus use the larger V6 pickup if you haven't already done that. You can also radius the corners in the suction passage including the pump housing and booster plate if you use that. Any restriction you can remove will help. Jim
All block passages are stock. I have a setup/tested stock cover from Underdog with the adj. reg. and booster plate. It was new (not TA unfortunately) cam bearings. Ill try the extra quart in a few hundred miles closer to my oil change. i always use a bosch 3423 or the ac/wix equivalent. Valvoline vr1 10w30.
