Oil starvation issues SBC HELP?

[joespanova]

Going back 14 years ago I lost an engine from what I thought was fatigue of an aluminum rod. There was evidence of oil starvation as the bearing was black and just appeared as though there was an oil starvation issue...............but I blamed the rod. I was probably wrong.
Fast forward to the last couple years and I've had everything from an oil pump bypass spring breaking ( lost that engine 3 years ago ) to constant oil pressure / starvation issues. It'll have great oil pressure until I make a hard pass or 2. At that point oil pressure drops and in at least 1 case I completely lost oil pressure and was fortunate to catch it before doing major damage. So , the attempt to remedy was to stop using K& N filters , use a WIX racing filter and use a bypass type filter mount ( dirty oil better than no oil ). Same eventual result in that oil pressure steadily dropped throughout the day / evening. Final round I ran the car with 20 lbs of oil pressure and kept my fingers crossed. At that point I decide to upgrade to a Dart block because of priority main oiling etc etc.
All the previous blocks ( 3 ) were Gen 1 blocks.
The latest block is a Dart Little M ( sportsman ) . So , I start the engine , great oil pressure ( Brad Penn breakin oil ). All week long start , run in some , get ready for the weekend. I think I'm good to go.........then UNBELIEVABLY the same problem is occuring with the Dart block! 2ND RUN PRESSURE IS DROPPING!
Only this time I have a NEW Melling 10552C pump. So , new pump , new block. Oil clearance .0025 /.003.
Engine 355 SBC , Brodix head , 14-1, No restrictors in block.
Moroso Ultimate 2 WET SUMP pan. Scraper.
Vac. pump pulls about 10"-12" vac .
AM I AT THE POINT WHERE A ROTOR TYPE STOCK PUMP CAN NO LONGER GET THE JOB DONE?
RPM range 8700-8900.
If so what do you recommend? Is it aeration? Bad pan design? Do I need to completely RETHINK my oil system? There has to be some common denominator here that transferred to each block.What about an accumulator?
Joe

[Alan Nyhus]

I'd make sure the vacuum pump isn't causing the issue.

[pmrphil]

OK, new block and pump. Same pan? Oil clearances strike me as a bit loose for aluminum rods. Is the oil getting too hot? Does the pressure gradually go down or does it just drop at a certain point or RPM? The pump should be more than sufficient.

[rboyle]

Is it the same distributor?

[joespanova]

Originally Posted by pmrphil

OK, new block and pump. Same pan? Oil clearances strike me as a bit loose for aluminum rods. Is the oil getting too hot? Does the pressure gradually go down or does it just drop at a certain point or RPM? The pump should be more than sufficient.

Same pan. No those oil clearances are spot on. Oil getting too hot? Doubtful. Pressure goes down as a result of bearing surface going away.
I made 2 runs today and the engine's coming out.
The vac pump issues has been mentioned by several others on Speed Talk. That's something I didn't give any thought to as my understanding is that high vac starts showing issues with wrist pins........I never see that.
I did change to a larger pulley and vac is about 5-6" at idle and I believe 10-12 throught the lights...............but I can't confirm that. I've never noticed it being too high but then I dont look at the vac gage during a run either.

[joespanova]

Is an accumulator a solution.

[carl hinkson]

Originally Posted by joespanova

Going back 14 years ago I lost an engine from what I thought was fatigue of an aluminum rod. There was evidence of oil starvation as the bearing was black and just appeared as though there was an oil starvation issue...............but I blamed the rod. I was probably wrong.
Fast forward to the last couple years and I've had everything from an oil pump bypass spring breaking ( lost that engine 3 years ago ) to constant oil pressure / starvation issues. It'll have great oil pressure until I make a hard pass or 2. At that point oil pressure drops and in at least 1 case I completely lost oil pressure and was fortunate to catch it before doing major damage. So , the attempt to remedy was to stop using K& N filters , use a WIX racing filter and use a bypass type filter mount ( dirty oil better than no oil ). Same eventual result in that oil pressure steadily dropped throughout the day / evening. Final round I ran the car with 20 lbs of oil pressure and kept my fingers crossed. At that point I decide to upgrade to a Dart block because of priority main oiling etc etc.
All the previous blocks ( 3 ) were Gen 1 blocks.
The latest block is a Dart Little M ( sportsman ) . So , I start the engine , great oil pressure ( Brad Penn breakin oil ). All week long start , run in some , get ready for the weekend. I think I'm good to go.........then UNBELIEVABLY the same problem is occuring with the Dart block! 2ND RUN PRESSURE IS DROPPING!
Only this time I have a NEW Melling 10552C pump. So , new pump , new block. Oil clearance .0025 /.003.
Engine 355 SBC , Brodix head , 14-1, No restrictors in block.
Moroso Ultimate 2 WET SUMP pan. Scraper.
Vac. pump pulls about 10"-12" vac .
AM I AT THE POINT WHERE A ROTOR TYPE STOCK PUMP CAN NO LONGER GET THE JOB DONE?
RPM range 8700-8900.
If so what do you recommend? Is it aeration? Bad pan design? Do I need to completely RETHINK my oil system? There has to be some common denominator here that transferred to each block.What about an accumulator?
Joe

I have block the oil filter bypass for 35 or so years now never seen any problems yet alot of my applications are circle track along with street and strip builds.

How does blocking the bypass cause bearing issues or loss of oil?? I would really like to know as I am not seeing any issues !!!!!

What pan are you running?

Some times to much oil in the pan will cause a problem.

Those R filters have a 51 Micron rating which will let alot of debris though into the bearings, The 1061 NAPA Gold has a 19 to 21 Micron rating.

If your running cam bearings with 3 holes that a lot of bleed off no put a vacuum pump in the equation now your sucking oil out through the cam and cam bearing.

Again to much oil maybe your problem and maybe a better pan may help.

Not knowing your lifter bore clearance maybe causing a big bleed off.

[Ed Wright]

Originally Posted by joespanova

Same pan. No those oil clearances are spot on. Oil getting too hot? Doubtful. Pressure goes down as a result of bearing surface going away.
I made 2 runs today and the engine's coming out.
The vac pump issues has been mentioned by several others on Speed Talk. That's something I didn't give any thought to as my understanding is that high vac starts showing issues with wrist pins........I never see that.
I did change to a larger pulley and vac is about 5-6" at idle and I believe 10-12 throught the lights...............but I can't confirm that. I've never noticed it being too high but then I dont look at the vac gage during a run either.

I don't think those bearing clearances "are spot on", but on the loose side. I don't ever run one that lose. One thousandth per inch journal diameter. That is all you need. That is not enough RPM to be a problem. What are you doing that you need aluminum rods? You understand that your already a little loose rod bearing clearances are getting looser as it warms up, right?
How much end play in your oil pump? I never run more than .001" end play on my pump impellers. If I open up a new pump and find more than that (often do) I lap the end of the pump housing until I get it there. Done that for years with zero issues.
What weight oil are you using?

[ss3011]

Is the plug installed in the block, under the rear main cap , that sends oil to the filter ? If missing it will bypass the filter, and may cause contaminated oil to ruin the bearings . Don't know if the Dart blocks are machined like a production Chevy block, but when I bought a couple of factory blocks that plug was missing .

[Greenlight]

Just curious, how much oil are you running and what oil pan (part number and manufacturer) are you using?

I'm leaning toward aeration.