408 SBC OIl Pressure Drops Under Heavy Acceleration

[Callmewaylon]

My 408 sbc has always had oil pressure drop under heavy acceleration. I'm running a Milodon 30908 pan that has a built in windage tray, Milodon 18314 pickup(I think) and Melling M55HV pump. My oil pressure hot is just over 25lbs hot and goes to 40lbs by 2000rpms. Then if you rev it up it will climb to 60psi at 6000rpms. Can hold it at high rpm and it never drops. Under hard acceleration right as I hit second gear the oil pressure drops back down to 40 and will then drop to 30 and slowly come back up to 40 by the end of the 1/4 mile. It did the same thing with a stock style Milodon pan so I tried adding the pan I'm running now with the windage tray, 6qt plus filter capacity etc. I'm starting to think it has something to do with how Milodon's pickup is located more forward in the pan instead of to the rear of the pan. Looking for ideas and suggestions. I've had the engine apart and the bearings look fine so it doesn't seem to be hurting the engine as it's had at least 200 passes on the track and street like this but it never fails to make me cringe when I watch the gauge. The only thing I can think to try next is to install that plate that Milodon sells to help stop oil from climbing the back of the pan and maybe a pickup that locates to the rear of the pan more.

[Alaskaracer]

You're going to get told that the pump is "sucking the pan dry"....which is total BS!!! What you need to do is address oil return in the engine...regardless of how much flow a pump is capable of producing, it will only produce what the engine clearances will allow.. Make sure all drawback holes are deburred, edges rounded. No gasket coving up part of the oil return from the heads. If so, cut it away so it's not impeding oil flow back to the lifter valley and crankcase...Make sure that your crankcase is vented properly if not running a vacuum system.

I had a 400 small block that I raced when I lived in North Carolina...Same pan and pump....NEVER had an issue with oil pressure dropping during the run. I paid attention to oil drainback and that was it. Funny thing, that engine is still running to this day....In the same car....

[RDY4WAR]

As mentioned, drainback can be a cause. High viscosity oil can be a cause as well. A 20W-50 molasses doesn't like to flow.

Another cause for that is excessive oil foaming/aeration. What oil are you using and how much are you using?

[Tom68]

My 408 sbc has always had oil pressure drop under heavy acceleration. I'm running a Milodon 30908 pan that has a built in windage tray, Milodon 18314 pickup(I think) and Melling M55HV pump. My oil pressure hot is just over 25lbs hot and goes to 40lbs by 2000rpms. Then if you rev it up it will climb to 60psi at 6000rpms. Can hold it at high rpm and it never drops. Under hard acceleration right as I hit second gear the oil pressure drops back down to 40 and will then drop to 30 and slowly come back up to 40 by the end of the 1/4 mile. It did the same thing with a stock style Milodon pan so I tried adding the pan I'm running now with the windage tray, 6qt plus filter capacity etc. I'm starting to think it has something to do with how Milodon's pickup is located more forward in the pan instead of to the rear of the pan. Looking for ideas and suggestions. I've had the engine apart and the bearings look fine so it doesn't seem to be hurting the engine as it's had at least 200 passes on the track and street like this but it never fails to make me cringe when I watch the gauge. The only thing I can think to try next is to install that plate that Milodon sells to help stop oil from climbing the back of the pan and maybe a pickup that locates to the rear of the pan more.

Too much oil would be my first guess, there's no back lip in that sump to stop the oil getting up into the crank, so you don't want to run it too high. Also has a wide pickup area, great for volume, crap for pickup without swinging baffles.

How fast a car are we talking, how many g's ?

[KnightEngines]

Try a thinner oil to start with, say 10/30.
If it improves it's a drainback issue.

Without pulling the engine down to open up the drainbacks you could try restricted pushrods - less oil up top is less to drain back.

[Callmewaylon]

I'm running Valvoline VR1 10W-30. Are runs 12.2 @112 consistently. When I freshened the engine up last winter(rings and bearings, upgrade to roller cam and better heads) I opened up the oil drain back holes at the back of the block and the front. I don't believe it's a drain back issue because it doesn't happen if you are sitting still and rev the engine to high rpm and hold it. Maybe too much oil? It's a pretty deep pan, but I've run it a qt low and about the same results. It's supposed to hold 6qts plus filter so I fill the filter as much as reasonably possible and then do the 6qts. I've used PF1218 PF2232 and WIX 51060(I think) filters. All with about the same results. The comment about no lip on the sump of the pan makes sense. The oil could be climbing the back of the pan and be getting wound up in the crank. The windage tray in this pan doesn't cover the back like some do.

[Callmewaylon]

This is a pic of the Milodon pump I had in the engine before. Std volume. The pan is just for illustration purposes. It makes you realize how far forward the Milodon pickup is. I have another pickup here and it would put the pickup almost directly under the oil pump. I have to think the forward pickup position is contributing to the issue under hard acceleration.

[cpmotors]

My 408 sbc has always had oil pressure drop under heavy acceleration. I'm running a Milodon 30908 pan that has a built in windage tray, Milodon 18314 pickup(I think) and Melling M55HV pump. My oil pressure hot is just over 25lbs hot and goes to 40lbs by 2000rpms. Then if you rev it up it will climb to 60psi at 6000rpms. Can hold it at high rpm and it never drops. Under hard acceleration right as I hit second gear the oil pressure drops back down to 40 and will then drop to 30 and slowly come back up to 40 by the end of the 1/4 mile. It did the same thing with a stock style Milodon pan so I tried adding the pan I'm running now with the windage tray, 6qt plus filter capacity etc. I'm starting to think it has something to do with how Milodon's pickup is located more forward in the pan instead of to the rear of the pan. Looking for ideas and suggestions. I've had the engine apart and the bearings look fine so it doesn't seem to be hurting the engine as it's had at least 200 passes on the track and street like this but it never fails to make me cringe when I watch the gauge. The only thing I can think to try next is to install that plate that Milodon sells to help stop oil from climbing the back of the pan and maybe a pickup that locates to the rear of the pan more.

You have a pressure problem, aka bearing clearance or internal leak.
I'd bet the leaks are aerating the oil, adding to the return issue.

[panic]

You need a vertical baffle in back of the pickup, taller than the (resting) oil level, to stop the oil wave rushing backward from acceleration, with big slots near the bottom to allow the oil to return.
A baffle in front will prevent the pickup from sucking air on panic braking.

[dfarr67]

Cavitation?
When the rear main is off next time- port the oil passages.

[abc]

Fairly simple to try a crank scraper, new pick up, and the plate under the pump to keep the oil from climbing the back of the crank. If you try the plate under the pump, make sure to recheck and set the drive shaft engagement.

[Callmewaylon]

My 408 sbc has always had oil pressure drop under heavy acceleration. I'm running a Milodon 30908 pan that has a built in windage tray, Milodon 18314 pickup(I think) and Melling M55HV pump. My oil pressure hot is just over 25lbs hot and goes to 40lbs by 2000rpms. Then if you rev it up it will climb to 60psi at 6000rpms. Can hold it at high rpm and it never drops. Under hard acceleration right as I hit second gear the oil pressure drops back down to 40 and will then drop to 30 and slowly come back up to 40 by the end of the 1/4 mile. It did the same thing with a stock style Milodon pan so I tried adding the pan I'm running now with the windage tray, 6qt plus filter capacity etc. I'm starting to think it has something to do with how Milodon's pickup is located more forward in the pan instead of to the rear of the pan. Looking for ideas and suggestions. I've had the engine apart and the bearings look fine so it doesn't seem to be hurting the engine as it's had at least 200 passes on the track and street like this but it never fails to make me cringe when I watch the gauge. The only thing I can think to try next is to install that plate that Milodon sells to help stop oil from climbing the back of the pan and maybe a pickup that locates to the rear of the pan more.

You have a pressure problem, aka bearing clearance or internal leak.
I'd bet the leaks are aerating the oil, adding to the return issue.

I measured the bearing clearances and all were in a normal range, crank end play was good. Maybe too much con rod side clearance? Where would an internal leak come from?

[rebelrouser]

I will go with several of the advice. Too much oil, poor drain back, too much oil to the top. Maybe even oil too thick. I would suggest an oil accumulator to cover up supply issues, especially if you cannot figure out the problem without blowing an engine. I have used one in the past. If you put a valve on it and close while engine is running you have oil stored to prevent dry starts.

[Tom68]

Maybe too much con rod side clearance? Where would an internal leak come from?

That at least we now no to be a myth, the bearing clearance regulates the oil not the side clearance.

You don't have a leakage problem, 6000 rpm stationary yields solid oil pressure, check it at the end of a pass if you haven't done it with oil hot

Any chance your pickup is sitting way off the floor of the sump, or less likely, too close to the floor of the sump ?

I wouldn't be reducing oil volume yet unless you know for a fact it's too close to the crank.

If you don't need the oil volume a narrower sump would be better.

Have you had a look at the underside of the pistons in this motor, I expect you'll see the front pistons are dark stained under the crown and the back pistons are shiny silver.

Yer that is a shit pickup position for a wide bottom sump in a drag car.

[1980RS]

This is a pic of the Milodon pump I had in the engine before. Std volume. The pan is just for illustration purposes. It makes you realize how far forward the Milodon pickup is. I have another pickup here and it would put the pickup almost directly under the oil pump. I have to think the forward pickup position is contributing to the issue under hard acceleration.

Do you see the problem? I do. The pickup is too far in the front of the sump. I just went through this with my BBC this year as the car launched so hard the oil ran from the pickup tube (in the front of the sump) but being a big dummy that day I did not see that on the gauge, but I did after watching the in car camera video. If you are drag racing, IMO the pickup tube needs to be closer to the rear of the pan, then one needs to make some baffling to keep oil from rushing to the front of the sump when you are de-excelerating. I have never had this happen on any of my engines before like the oiling issue you have had and it cost me a nice bottom end this year. Next year I will use a pan and sump the pickup tube to the rear of the pan like my Moroso one are. Change to a different pan and pickup tube and your oiling issue will be gone IMO.