A differant oil problem......LONG!

[Bill W.]

I am helping a friend get a new engine running properly in his 1965 Corvette. The engine is a 406 CI small block, roller hyd. cam, aluminum heads and a "380" Rochester fuel unit. This engine was assembled by a respected shop here in Albuquerque.
When we first fired the motor no problem was evident, oil pressure 60 PSI and steady. After breaking in the cam for 30-40 minutes at verious RPM we drove car on a 5 mile test run. Under slow acceleration to any RPM (up to 5000 RPM limit) oil pressure is steady at 60 PSI. If we accelerate with 2/3 throttle or more oil pressure will drop like a rock to 20 PSI at which time we back out of the gas and pressure goes back up. The problem is NOT RPM related. We can run the motor at a steady 4000 or 4500 RPM and pressure is steady as a rock. The problem is acceleration related.
Our first thought was pump pickup placement or plugged oil filter from assembly lube. We pulled the pan, bottom of pickup is 3/8" from bottom of pan. No problem there. Pulled filter and filter adapter, filter felt heavy (this is a WAG on my part) noticed that the bypass valve on the filter adapter had been removed and plugged with a hex plug. Replaced adapter with one having a working bypass, new filter installed, added six quarts fresh oil and went for test drive. Same problem. Good pressure at any steady state RPM, but under acceleration pressure will drop like a rock. Where do we look next? Thanks, Bill

[Duke W.]

Re: A differant oil problem......LONG!

It sounds like dynamic loading is uncovering the pickup. What are the pan configuration details. Sometimes "excessive baffling" can cause problems under high dynamic loading.

Duke

[Bill W.]

Re: A differant oil problem......LONG!

Duke, The oil pan is a GM six qt. pan with swinging trap door, but no baffle above it. We have considered the pickup being uncovered during acceleration and tryed adding an extra qt. of oil. This had no effect.
This motor pulls HARD, I suppose it could plie all the oil at the back of the pan and uncover the pickup. How can we test this theory without buying a high dollar oil pan?

[Duke W.]

Re: A differant oil problem......LONG!

Okay, it sound like the OE "big" pan used on mechanical lifter engines from '63 to '65, but it's missing the top horizontal baffle, which along with the trap door keeps the oil from flowing forward under heavy braking. What about the windage tray. I assume that with the long stroke configuration you had to leave it off.

The first thing you should do is run some tests to determine oil pressure behavior under both heavy braking and cornering.

About a decade ago I was having some oil pressure problems with my Cosworth Vega under heavy braking at track events.

I borrowed a spare pan from a buddy, cleaned it up and ran a bunch of tests in my kitchen sink using water. Tilting the pan 45 degrees simulates 1 g loading.

Using an assumption that three quarts were up in the engine at high revs with only about 1.5 quarts was in the pan, I could see that the pickup was being uncovered under heavy braking.

So I fabricated a prototype horizontal baffle using a sheet of thin flat plastic from the shallow bottom of the pan back several inches, which created and oil trap to prevent the oil from flowing forward to the shallow portion of the pan under braking, and 1.5 quarts was sufficient to keep the pickup covered when the pan was tilted 45 degrees forward simulating 1 g braking.

It worked, but I had one other issue. The unbalanced second order vertical shaking force beats up stamped sheet metal components on four cylinder engines. Fortunately, at the time, I had a CV buddy who was doing work on the F-22 and had access to the ANSYS structural analysis program to do a modal analysis. The initial model with just a turned down rear lip was not stiff enough, so we added an "X" stiffening rib, which got the lowest resonance frequency above 8000 revs.

Fortunately I also had a buddy who owned a sheet metal shop at the time, which is where I fabricated the part and another buddy welded the baffle into the pan.

It's great to have buddies with the requisite skills when you are trying to solve this kind of problem.

Run some braking and cornering tests and let us know the results.

Another issue could be oil drainback or the crank dragging through the oil.

Duke

[Clem Z.]

Re: A differant oil problem......LONG!

a lot of time oil pans with a swinging trap door if put on the engine on a engine stand with the engine upside down the trap door can be stuck in the open position. always install these pans with the engine right side up on the stand. there baffles that go between the oil pump and rear main cap that fits against the back wall of the pan that will prevent the oil from running up the back of the pan during hard acceleration. i used these on all drag engines. http://www.jegs.com/p/Moroso/745530/10002/-1 i would also install the GM windage tray to be on the safe side

[Bill W.]

Re: A differant oil problem......LONG!

Duke & Clem, Thanks for the suggestions. Curing this will not be a quick fix, but we will run some tests and get back with more info. Clem, while we had the pan off yesterday we checked the trap door, it swings freely. We do not have the baffle that is normally used with this pan. (the one that bolts to the five main bearing studs) Not sure it would clear the long throw of the crank. More later, Bill

[Duke W.]

Re: A differant oil problem......LONG!

The later windage tray used on 350s was "semi-circular" rather than flat as on 327s - probably to clear the longer 3.48" stroke.

What is the stroke of this "406"?

Duke

[Clem Z.]

Re: A differant oil problem......LONG!

The later windage tray used on 350s was "semi-circular" rather than flat as on 327s - probably to clear the longer 3.48" stroke.

What is the stroke of this "406"?

Duke

3.75" i would guess. the GM perf parts book say to elongate the bolt holes to use on 400 cu in engines as the studs are farther apart than a 350. use part #3927136 windage tray and the pan is 360450 that matches this windage try

[Bill W.]

Re: A differant oil problem......LONG!

Duke & Clem, You are correct, stroke is 3.75". I did not know of a baffle for the back of the pan. I like the idea of preventing the oil from climbing the back of the pan. The later model "round" windage tray would probably help also. Bill

[Bill W.]

Re: A differant oil problem......LONG!

Clem, We have ordered the rear pan baffle from Jig's, should have it installed by early next week. I'll post results, Bill

[Bill B.]

Re: A differant oil problem......LONG!

Bill - High volume oil pump, shallow oil pan will definitely have the same effect. Also check the oil pick up it should be 3/16'' from the floor of the pan......just a suggestion....Good luck!

Bill

1961 Black/Silver/Red Int. 283/315 FI
power windows. Frame off 65% completed.
1989 hard top daily driver 165,000 miles

[Duke W.]

Re: A differant oil problem......LONG!

3/16" sounds pretty tight. Maybe Clem can confirm.

A long time ago an old mechanic told me about a Vega failure mode that I had never heard of. The early Vegas were pretty low and didn't have much ground clearance or suspension jounce travel. It was not uncommon for them to "bottom out" and that could shove the oil pan against the pump pickup, which could result in oil starvation.

My '72 Vega GT never suffered that fate, and my '76 Cosworth Vega rides about one-half inch higher due to longer springs that GM began using that year.

Duke

[Clem Z.]

Re: A differant oil problem......LONG!

3/16" sounds pretty tight. Maybe Clem can confirm.

A long time ago an old mechanic told me about a Vega failure mode that I had never heard of. The early Vegas were pretty low and didn't have much ground clearance or suspension jounce travel. It was not uncommon for them to "bottom out" and that could shove the oil pan against the pump pickup, which could result in oil starvation.

My '72 Vega GT never suffered that fate, and my '76 Cosworth Vega rides about one-half inch higher due to longer springs that GM began using that year.

Duke

3/8" to 1/2" check with modeling clay.

[Bill W.]

Re: A differant oil problem......LONG!

Clem, Duke & all else who suggested fixs;
Good on all you people! We installed the rear baffle from Jeg's last night. This is a simple piece of metal sandwiched between the oil pump and the rear main bearing cap (cost about $6 bucks). It extends back toward the rear of the pan, leaving roughly 1/8" to 1/4" between it and back of pan. With this in place we can now use full throttle until we run out of road or the cops get us! Oil pressure is steady as a rock at 60 psi.
Clem, this was a quick, effective fix. Thanks for letting us know this piece was available. Bill

[Clem Z.]

Re: A differant oil problem......LONG!

Clem, Duke & all else who suggested fixs;
Good on all you people! We installed the rear baffle from Jeg's last night. This is a simple piece of metal sandwiched between the oil pump and the rear main bearing cap (cost about $6 bucks). It extends back toward the rear of the pan, leaving roughly 1/8" to 1/4" between it and back of pan. With this in place we can now use full throttle until we run out of road or the cops get us! Oil pressure is steady as a rock at 60 psi.
Clem, this was a quick, effective fix. Thanks for letting us know this piece was available. Bill

before these were avaiable i used to make my own baffle for all my drag race engines.