I suggest pulling the oil pan and seeing how clean it and the pickup screen is. I'd be willing to bet the pickup screen is somewhat clogged enough to notice a difference at higher rpms. If not, make sure it's sitting low enough in the pan. My 91 S10 4.3 did the same thing as your Z does at WOT. I never got a chance to pull the pan and clean stuff out, but I did run some of that STP engine flush through twice when I had the truck. I'm almost positive that was the cause of the pressure drop in it.

The sending unit on my Jeep is on top of the block, well away from the pump, and I get no fluctuations in pressure at WOT. It's always been rock steady at 60psi anywhere above 3000 rpm even at 138k miles so I kinda doubt the location of the sending unit matters that much. hope this helps

Jason

 

Hmmmm, interesting thread. I too have the oil pressure fluctuation problem and it is very similar to what you guys describe. I was wondering WTF it could be. I just figured it was excessive bearing clearances.

 

replacing with a stock pump will not fix the problem, and besides a clogged pickup very low oil pressure at idle is a sign of too much main bearing clearence. i do work in a race engine shop and ive pulled hundreds of motors apart and never seen a "bad oil pump" they either work or they dont

 

i just test the car again. when it was cold, the psi does not drop.
i stomp on it a few times and it held steady at 75psi. the temperature was 140-150 degrees. could this be because my oil is still thick and cold??

also when i replace the oil pump, the pick up tube was still on there and it was as clean as can be.

btw, i think on 93s the oil sending unit is on the bottom, not like the 94+ years.

 

Anybody else have anything to add?

 

Yeah, anti-cavitation oil pump as mentioned before; replace with it and forget it.
Doug

 

did you personally have this problem as well? and you fixed it with hte anti-cavitation oil pump?

 

No mine does not have that problem. Years ago, when LT1's were first being modded this same issue came up...it seemed to follow only cam/heads upgrades or those with other power adders. They found they could reduce it by using thicker weight oil, but not completely eliminate it. Someone commissioned Moroso to cut the anti-cavitation reliefs in their pump and it was being sold by Summit or Jegs. After installing the new pump, the problem was resolved. Might want to search out the internet on it, or run it the way it is and wallow out some mains.
Doug

 

What I want to know is, why is it that this problem rears its ugly head after a cam swap? Why is this not an issue with the stock engine?

 

my car does the exact same thing. idles at 20 psi and maxes out at 40 psi around 1700 rpms but WOT i see very little increase in pressure as well as that dip everyone talks about at 4500ish. i use regular valvoline 10w30 and i cant say for sure if the problem came about after my cam install b/c to be honest i rarely checked it unlike now its almost look at more then my speedo is.

 

Anyone have any info on the anti-cavitation pump by moroso? Anyone install it or know someone who has? Part numbers, etc?

Here's an interesting thread I found:

http://web.camaross.com/forums/showt...ght=cavitation

 

http://www.moroso.com/catalog/catego...?catcode=14444


#22100

 

If I remember correctly, these came with 3 relief springs. Seems like the 60# spring and a washer/shim was the preferred setup at the time. It's been a while since then.
Doug

 

mine did the same thing, but im fixing the problem now, its called all my bearings are tor up from the floor up... lol, i think mine it started with cam bearings, the deris from that went to the rod bearings, and the debris from that went to some of the mains.... but rebuilding it should solve my problem...

BTW my car was beat every day it was drivin, all the way to 200k+ miles on it..... it is a 96 trans am

 

I have a 94 with 111,000 miles on it and oil pressure at idle is a public hair above 20 and cruising it is a public hair above 40. I over revved it a few times and it is still the same, only time it changed was going to 10W-40 and then at idle it was 30 and at cruising it was about 45ish....this is even after full warm up I too am interested in a better oil pump even though I might not need it it is safe insurance..