I recently upgraded to a 406 with TPIS/AFR heads. Everything else is in my signature. Anyway, if I sustain rpm over 4000 rpm, my oil pressure begins to drop. It goes up with rpm as expected but then drops off. I have a standard volume Melling oil pump and a stock pan. I pulled the motor hoping to find something with pan to pick-up clearance, but had no luck. I have proper clearance and the pick-up screen is clean. I cut open my oil filter (AC 1218) and it looks fine (not collapsed). The motor has less than 2000 miles on it. I drained about 4.5 quarts so it wasn't low. The motor is currently out of the car.

I do have a solid roller cam/lifters. Do I need oil restrictors? I've seen two different types, but am not sure of their proper usage. I don't have a windage tray either. Maybe the big internally balanced crank is whipping up the oil?

Any help or insight is appreciated.

 

It's possible the pan is running out of oil at the high rpm. Do you have restrictor screens in the lifter valley or drain holes blocked off?

Since you cut the filter open, recheck the media. Cut a section of pleats out of the filter. Squish them in a vise to remove the oil then open them up for inspection. Any metal will be easier to see.

Oil restrictors just limit how much oil reaches the lifters and rockers. Solid rollers don't need a lot of oil. The main and rod bearings are the primary users of engine oil.

Since your pan is off, pull your main bearing caps and check the bearings. If there's been a lack of oil pressure problem, it will show up there first.

Hopefully I've solved my dragstrip oiling problem by installing a Moroso 3 quart oil accumulator.

 

Thanks for the reply. I'll check the filter this evening. I haven't restricted any of the drain back passages. I've heard of AFR's having drain back problems though. I'm going to check the bearings since I'm to this point. I've heard of other people having problems with the filter media collapsing or just being a restriction especially with 20W50 oil. Shouldn't it bypass the filter though?

 

It should. That's the purpose of the bypass valve in the filter housing. Pressure goes into the filter, pressure goes out. If outlet pressure is lower than inlet pressure then the filter is plugged. The difference in pressure allows the bypass valve to open so the engine doesn't starve for oil.

The only time you would have problems with 20w50 oil is when it's cold. Once the engine reaches operating temperature, even 20w50 will flow free enough.

My race engine has a 7 quart pan and a 3 quart oil accumulator. I use 9 quarts of 20w50 and 1 quart of Lucas oil stabalizer.

 

What kind of gauge are you using, electric or mechanical??

 

I have both an autometer mechanical and the stock electrical gauge in the dash. They both show the same thing.

I removed the main caps. They all have light scuffing on them. Some have a small scratch like grooves from foriegn material. The rear cap bearing, however, has some blueing to it like it may have gotten a little warm. I'll probably disassemble the complete engine, clean everything and replace the bearings and check clearances. Unfortunately, I bought the short block off Ebay and it seemed a little dirty. I guess if you want something done right, you have to do it yourself. I don't think its the cause of my problems though.

I have just under 3/4" clearance between the pick-up and the pan. Is that too much? The pick-up is parallel to the bottom of the pan. To get it closer, the pick-up would be angled downward slightly.

Is there a possibility that too much oil is going to the valvetrain and draining the pan? Will restrictors help this?

 

Oh, and I checked the filter media. They're were a few specs of metal sprinkled here and there, but not much considering how new the engine is. (still breaking in)

 

I'm having a similar problem in which the main bearing clearance are suspected. Can you remove the main caps, check the bearings out, then if everythings OK, re-torque the main caps back down with the same old bearings, or do you have to buy new bearing eveytime time you un-bolt a main cap?

Does the same thing go for rod bearings if you remove the rod, but he bearing looks OK?

Basically, I want to know if I can tear down my short block, and reuse the bearings if they're OK?

 

You can reuse your bearings. Just make sure you put the same bearing back in the same spot and orientation. That way the wear patterns are the same. Make sure everything is clean and use some assembly lube for start-up. Same goes for the rod bearings.

Bearings are pretty inexpensive, so you can also put new ones in for little cash. If you can afford it, have the crank polished and recheck clearances.

 

I'm kind of in the same boat as you. I have low pressure when cold(20lbs with 20w50) and when it warms up and i drive it the oil pressure slowly drops to 0, and never comes back up. Some have mentioned a misaligned main bearing, and clearances. I had good oil pressure before. It is a fresh rebuild, maybe 600miles, in which I had good oil pressure. how do i check for bearing misalignment, and what clearances should be and where?