[Joshsox]

Hi! Just keen to hear some opinions with an interesting issue I've had with my 77 Trans am.

Shortly after buying the car without a working oil pressure gauge I spun a bearing whilst having some fun including high rpm pulls.

I got the 400 motor rebuilt with an eagle 461 bottom end kit and fixed the oil pressure gauge.

From there any heavy acceleration past maybe 4k rpm saw the oil pressure start dropping from 80psi to 40 or less? Once I let out of the accelerator pressure would return to normal.

I think this may have been the cause of the previous engine failure. The only thing that stops the issue is dropping about a quart/litre of oil out. Pressure then stays all the way to 6500 but the engine has about a quart less than the specified 5 quarts.

Engine is happy below the low mark on dipstick

The engine retains the windage tray and factory sump.

Any ideas on what could be causing this issue when adding the right amount of oil?

[johnta1]

What kind of oil and weight of it?


Sounds kind of strange.

[Sirrotica]

The only way I could see what you're describing happening is, that you're aerating the oil without any windage control at high RPM. Draining a quart out lowers the oil level below the crankshaft so that it's not getting whipped into a oil smoothie, and trying to push air and oil through the system. When an aerated liquid is under pressure it is able to be compressed, whereas pure liquids can't be.

I have no idea what your builder used for windage control, but maybe there isn't any tray, scraper or other baffling in the pan. Or it isn't doing it's job.

Pontiacs have a very wide pan compared to most other V8s and that extra width can cause windage, and oil slosh more so than say a chevy with a much narrower pan.

Having raced both auto cross, and on dirt oval tracks I can say for sure that stock Pontiac oil control is somewhat lacking.

[68WarDog]

The oil system should be a total of 6 quarts , 1 in the filter, 5 in the pan. 80 psi cold is common, with 40-50 running, if oem oil clearances.

[gtobird]

Originally Posted by Sirrotica

The only way I could see what you're describing happening is, that you're aerating the oil without any windage control at high RPM. Draining a quart out lowers the oil level below the crankshaft so that it's not getting whipped into a oil smoothie, and trying to push air and oil through the system. When an aerated liquid is under pressure it is able to be compressed, whereas pure liquids can't be.

I have no idea what your builder used for windage control, but maybe there isn't any tray, scraper or other baffling in the pan. Or it isn't doing it's job.

Pontiacs have a very wide pan compared to most other V8s and that extra width can cause windage, and oil slosh more so than say a chevy with a much narrower pan.

Having raced both auto cross, and on dirt oval tracks I can say for sure that stock Pontiac oil control is somewhat lacking.

At first, I thought it was a problem with the pressure relief spring in either the oil pump or oil filter mount, but that would not explain the oddity of pressure being normal when the oil is low. Your diagnosis sounds correct to me. Would have to be something funky in the oil pan, windage tray, etc. What kind of oil pan does it have? Also, a long time ago, I watched an episode of Boyd Coddington where they built a SBC and the oil pressure was low. As I remember it (my memory sucks and is faulty) it turned out the oil pump intake was too close to the pan. I'm just wondering if the oil pump intake is somehow sucking air. Is it the same oil pump?

[Jay S]

I had an engine once that would loose oil pressure at high rpms and when you backed off the throttle the pressure came back. Eventually it lost all oil pressure and you had to shut it off for the pressure to come back. Figured out it was the oil filter causing the issue. Inspected the filter and the filter element was collapsed. The problem started after a cold start up in the winter. I doubt that is it, but it is always best to start with simple stuff first. Cause my next thoughts are not simple to fix.

I don’t think it is a windage issue, my guess is that another issue creates an aeration issue, and the oil level is nursing another issue, more or less a symptom from something else. Such as, sometimes the pickup can fall off the pump and cause pressure loss at high RPMs. Similar effect to having the pickup to close to the bottom of the pan, when the oil gets some extra aeration it looses pressure, oil pump starts sucking air. Pulling the oil thru a proper working pickup screen helps with aeration. There could be casting flashing inside the pickup on the pump that could cause that issue. Partially plugged pick up screen can do it also, as can not enough pan to pickup clearance.

My guess is the pickup screen is partially plugged in your engine, possibly from using too much silicone on something. I have worked on engines that had plugged pickup screens that acted very similar to what was described. Unfortunately all those issues except the filter, require a lot a work to fix, cause the engine usually comes out.

[Sirrotica]

Originally Posted by gtobird

At first, I thought it was a problem with the pressure relief spring in either the oil pump or oil filter mount, but that would not explain the oddity of pressure being normal when the oil is low. Your diagnosis sounds correct to me. Would have to be something funky in the oil pan, windage tray, etc. What kind of oil pan does it have? Also, a long time ago, I watched an episode of Boyd Coddington where they built a SBC and the oil pressure was low. As I remember it (my memory sucks and is faulty) it turned out the oil pump intake was too close to the pan. I'm just wondering if the oil pump intake is somehow sucking air. Is it the same oil pump?

Could be a pickup problem if it was consistent, taking out 1 quart shouldn't have any effect on a pickup too close to the bottom of the pan, IMO.

[Joshsox]

Thanks for the ideas. Being only high rpm with a high (normally full) oil level I think I need to pull the sump and see what's going on with the sump and windage.

[steve25]

First off and thank God it’s this way, Pontiac engineering put the oil pump way deep into the pan so it’s aways sitting in at least 3 Qt of oil under normal driving conditions and even without a baffled pan.
Also its gravity fed so it does not have to suck oil up a long 5 inch tube as in some other motors/ brands.

If by chance your internals of your oil filter has collapsed as suggested, yes that could drop the pressure, but once it does collapse you will nevef see your maximum oil pressure achieved again on your gauge.

I am willing to bet that due to your findings thst all is well when running a Qt low that your static oil level is high enough to have the top of the oil level bleedjng into the windage tray if there is one.

And if there is not one then the result is the same, a whole lot of oil is getting kicked up by the crank and blended with a lot of air.

Note that aerated oil is what you are seeing taking place on your oil gauge when the pressure is seen to drop.
You need to remember that air is compressible and a liquid such as oil is not.
The bad thing about this all is that aerated oil of no matter how high a pressure does not provide the needed strong oil film to keep parts from touching each other !

I would just consider running the motor a Qt low as you have found out works as intended, or get a better oil pan that suits your wildest driving times.

If you really are pushing your cars handling and whatever oil system it may have to the max then I would install a Acusump on the car as added insurance.

[Half-Inch Stud]

Hard right turns (yes in a Trams Am, or any vehicle) would reveal low oil level in your PMD oil Pan.

Add oil until the gauge doesn't dip, or use a re-designed oil pan.

[steve25]

Also just to keep the info straight here, a 77 400 did not start life with a windage tray as far as I know.

And just so we have your info right you stated that when you got the car the bearings went south when spinning to a high rpm.
1) was the 400 at that time stock?
2) how high did you spin it, if stock that cam would be hard pressed to go 6K ?
3) reving a motor that’s new to you in a used car above 5K with a known non working oil pressure gauge is asking for trouble, no?

[PunchT37]

Dipstick accuracy?

[Jay S]

Originally Posted by steve25

Also just to keep the info straight here, a 77 400 did not start life with a windage tray as far as I know.

And just so we have your info right you stated that when you got the car the bearings went south when spinning to a high rpm.
1) was the 400 at that time stock?
2) how high did you spin it, if stock that cam would be hard pressed to go 6K ?
3) reving a motor that’s new to you in a used car above 5K with a known non working oil pressure gauge is asking for trouble, no?

Yes, and if it is an actual 1977 engine, it would have a baffled pan from the factory and no windage tray, and also be a weaker 500557 block. If that is what it is, there are other issues to be concerned about, and needs pulled and inspected to find the issue.

[mgarblik]

Couple questions after reading and thinking about this. 1. Where are you getting your oil pressure input from? Factory electrical gauge, sender on filter housing? Mechanical pressure gauge, port on housing? Pressure port on top of engine? Somewhere else? There has been some controversy about proper oil fill on Pontiac engines based on year, oil pan used and filter used and dipstick markings. I have never been able to 100% sort this all out. But it seems to me 77 models were 5 Quart capacity with a filter installed total. If you have a stock pan and dipstick I would drain the oil and remove the filter and let it drain about 1/2 hour. Then install a new filter and 5 quarts of oil and run a minute, let it settle and look at the dipstick. Overall, it does sound like aeration of the oil. As a side note, very few Pontiac engines (non-dedicated race), make usable power above 6000 RPM's. This is especially true of anything with a flat tappet hydraulic cam. Most likely it is about done at 5200-5300 RPM's. Properly built, should be fine to 6000 RPM's but anything above that is asking for possible trouble with nothing to gain. JMO.

[GoGoat]

Reading all of this is very interesting. I have a question. Would a snake camera be beneficial to see the windage tray and maybe height of pickup screen and if plugged. Just a thought. Good Luck.

[Jay S]

Originally Posted by Jay S

Yes, and if it is an actual 1977 engine, it would have a baffled pan from the factory and no windage tray, and also be a weaker 500557 block. If that is what it is, there are other issues to be concerned about, and needs pulled and inspected to find the issue.

I am guessing that since the engine retains a stock windage tray the engine is not a 1977. There are no provisions on the main caps to run a factory windage tray on a 77 block.

I think adding a quart of Lucus oil stabilizer may lessen aeration. Easy to enough to try.

[steve25]

I agree the Lucus might help, but I think it’s Bandaid and chewing gum fix applied to what is a serious issue once a certain rpm is reached and a longer stroke crank with deeper / offset counter weights only digs deeper into a high unneeded oil level!

[i82much]

A few things to consider:

(1) Maybe add a Moroso or Canton accumulator, might save your engine while you figure this out.
(2) Capillary action can do some weird things and give you odd readings on the dipstick.
(3) Check both sides of the dipstick, if the oil is much higher on one side than the other, you need to figure out why.
(4) Not exactly the same symptoms, but I noticed I lost about 15 psi at idle when my 6.0 vortec 2500HD engine was overfilled by a quart, went back to normal after an oil change with the correct fill level.
(5) Any signs of blowby, dipstick being pushed out, etc.? Also, any chance oil is returning slowly?
(6) If all else fails, run it a quart low with the accumulator and you should probably be fine.

[Steve C.]

When evaluating total engine oil capacity a tid bit to consider, most common oil filters used do not hold one quart of oil. Next time you change filters fill the new filter and then let it soak up the oil. Tap it a few times for any trapped air and fill it again. Do this a few times until it won't take any more oil and you will find less than a quart poured into the filter. I've done this on a larger WIX 51049 filter and found it holds 'about' 3/4 quart.


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[Steve C.]

Rhetorical question.... how much oil is up inside the engine at higher rpm.


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