[SusieQ]

I read that the oil pump pickup screen for a Pontiac 400 should be anywhere from 1/2" to a 3/8" from the bottom of the pan. But then I read in another place that it should be closer at 3/8 to a 1/4" from the bottom. So I thought I'd ask the pros on PY Forums! What do you guys recommend?

Susie

[steve25]

There's a cast in locating boss ( small nub ) on the pump body that sets up how far above the bottom of the pan the pick up can go when installed.

[Tom Vaught]

Originally Posted by steve25

There's a cast in locating boss ( small nub ) on the pump body that sets up how far above the bottom of the pan the pick up can go when installed.

Agree with above.

If you had a deep pan depth and a custom oil pick-up would would adjust the screen height to get close to that 3/8" dimension.

I personally like the 3/8" number and will take the 7/16" number as the pick-up is typically not totally flat on Pontiac pumps with factory pick-ups. I try not to be below the 5/16" number and prefer not to be even be there. I avoid having the pick-up at 1/4" from the bottom, if I can.

Others might have different opinions. The notch in the pump is a pretty good locator though.

Tom V.

[mrennie]

My experience with a stock pump and replacement oil pan was that with the screen in the notch where it should be, I was getting more like 5/8". This was measured by putting a loose ball of aluminum foil on the pickup then bolting down oil pan to crush it, then take back out and measure. Adding the oil pan gasket would have added another 1/8" of clearance.

I found that trying to get closer by rotating the pickup just tilted it and readings were close on one end and too far on other end.

My point being that if the pan and pickup tolerances are off a bit, you may be limited on adjusting it any closer.

[SusieQ]

Originally Posted by mrennie

My experience with a stock pump and replacement oil pan was that with the screen in the notch where it should be, I was getting more like 5/8". This was measured by putting a loose ball of aluminum foil on the pickup then bolting down oil pan to crush it, then take back out and measure. Adding the oil pan gasket would have added another 1/8" of clearance.

I found that trying to get closer by rotating the pickup just tilted it and readings were close on one end and too far on other end.

My point being that if the pan and pickup tolerances are off a bit, you may be limited on adjusting it any closer.

Initially, I did the same thing with the ball of aluminum foil just to get an idea of how far that notch was from the bottom and came up with the same results...which I'm thinking is way too high is it not?

[Tom Vaught]

I have never been a fan of Aluminum foil as it does not hold its deformed shape exactly after being compressed.

I have some chrome metallic tape used to seal up dryer discharge tubes that send the dryer moisture outside. I tape a couple of pieces of that over the pick-up screen. It
keeps the "Play Dough" from entering the screen.
I put a 1/2" block of flat "dough" inside the pan and the bolt up the pan/gaskets to pan torque specs.

I then remove the pan and then measure the different heights on the dough.
Different way of doing it vs other ways but I know exactly in one operation
where the pick-up screen is vs the bottom of the pan. Kids play dough from
Hobby Lobby is cheap and never wears out.

Tom V.

I remove the chrome metallic tape and the play dough from the pan, lol!

[SusieQ]

Originally Posted by Tom Vaught

I have never been a fan of Aluminum foil as it does not hold its deformed shape exactly after being compressed.

I have some chrome metallic tape used to seal up dryer discharge tubes that send the dryer moisture outside. I tape a couple of pieces of that over the pick-up screen. It
keeps the "Play Dough" from entering the screen.
I put a 1/2" block of flat "dough" inside the pan and the bolt up the pan/gaskets to pan torque specs.

I then remove the pan and then measure the different heights on the dough.
Different way of doing it vs other ways but I know exactly in one operation
where the pick-up screen is vs the bottom of the pan. Kids play dough from
Hobby Lobby is cheap and never wears out.

Tom V.

I remove the chrome metallic tape and the play dough from the pan, lol!

So Tom, you suggest that I adjust it past the notch if the notch is too high correct? (Which it is.)

I'm making a bracket as we discussed a few weeks ago to hold the tube so I'm not concerned about it moving out of place. I bought the metal just yesterday. Just haven't got around to fabricating it yet. I'll share a pic when I'm done and you guys can tell me what you think.

I made a little measuring device to check pan depth and pickup clearance, but Play-Doh sounds like a lot more fun! Thanks for the tip!

[grivera]

Originally Posted by SusieQ

Initially, I did the same thing with the ball of aluminum foil just to get an idea of how far that notch was from the bottom and came up with the same results...which I'm thinking is way too high is it not?

What is your measurement?

[SusieQ]

Originally Posted by grivera

What is your measurement?

It was roughly a 1/2"

[lust4speed]

The inside area of the 3/4" outside diameter pickup tube is about .33 square inch. The area available under and around the pickup sitting a quarter inch off the pan is about 2.75 square inches which is a very safe amount. Or did I blow it on the math?

[Tom Vaught]

Not by very much, LOL!

Pick-up screen diameter is 3.6 inches.
Area of the pickup if no solid plate across the screen = 10.2 square inches.
So you subtract out the blocker metal bar which is 3.6 inches long by 1.3 inches wide
so that piece blocks 4.68 square inches of the ideal screen area.

So 10.2 square inches minus 4.68 inches = roughly 5.5 square inches of screened pick-up area.

5.5 square inches vs the oil pump screen pipe diameter .600" diameter

Lots of screened area vs the pipe flow area.

Tom V.

[Tom Vaught]

The .600" is the inside diameter which affects the flow rate.

Ideally you would be quite a bit larger on that suction pipe inside diameter dimension for best flow rate with smallest restriction before the pump. Very common on modern small engines to have a 3/4" inside diameter inlet to the pump.
Aston Martin V-12 engines used a inlet pipe closer to 1" inside diameter.
The .600" inside diameter is designed for a low rpm engine.

Tom V.

[chiphead]

That's why I like the Milodon scoop type pickup, it has a very large and short intake pipe between the scoop and the intake of the pump. It does have a 90* turn, so that's not great. There's always a trade off

[Tom Vaught]

One radiused 90 degree turn is not going to hurt you on flow very much.
Charlie66 did a very nice job modifying a 90 degree sharp turn "Box" pick-up into a softer radius
turn for his turbo 4 cylinder engine. It looked great.

This is a 455 SD pick-up with a nice radius turn into the pump but it needed to have a different design entry to make it work well.

Tom V.

[lust4speed]

Getting back to the original question which was how far off the bottom of the pan could the oil pump pickup be placed. The problem might be looked at like computing the area of an air filter, and using this to figure out the capacity under the pickup when 1/4" off the floor. Thinking of this area like the circumference of a cylinder that is the diameter of the pickup and the height being the distance off the floor. We can use Tom's 3.6" screen diameter and this produces a circumference of about 11". Take the 1/4" height from floor to pickup and that gives 2.75 square inches of effective area the oil has available to pass through. This is only about half the capacity of the screen area but many times over the flow rate of the pickup tube area which will be the choke point.

So thinking 1/4" would be totally safe? Distance could be less according to the math, but no reason to push the clearance any tighter.

[Steve C.]

A fwiw, Canton recommended pickup to pan clearances of 5/16-3/8 inch. And mention the gaskets will add some additional clearance.

.

[Tom Vaught]

Originally Posted by lust4speed

Getting back to the original question which was how far off the bottom of the pan could the oil pump pickup be placed. The problem might be looked at like computing the area of an air filter, and using this to figure out the capacity under the pickup when 1/4" off the floor. Thinking of this area like the circumference of a cylinder that is the diameter of the pickup and the height being the distance off the floor. We can use Tom's 3.6" screen diameter and this produces a circumference of about 11". Take the 1/4" height from floor to pickup and that gives 2.75 square inches of effective area the oil has available to pass through. This is only about half the capacity of the screen area but many times over the flow rate of the pickup tube area which will be the choke point.

So thinking 1/4" would be totally safe? Distance could be less according to the math, but no reason to push the clearance any tighter.

I am thinking years ago, that I did the same calculation and that was why I used the 1/2 height because the area around the screen matched the screen area. We also know that a higher pressure suction on a device, be it a carb or head tested at 20.4" of water vs tested at 28" of water) increases the flow reading thru the tested device. Now if you have a large inlet, be it a carb or a Aston Martin inlet pump from Luhn Performance you know that pump is not going to be pulling very hard to get a given flow.

Tom V.

[mrennie]

Perhaps I am missing the obvious, but something that is fuzzy to me...

...what negative effects are there if the pickup is higher off the pan floor than ideal?

I understand that the pickup cannot be too close to the pan, or else it hinders suction and could affect flow.

But what bad happens if the pickup is say, 1" off the floor? The only thing obvious to me is that you loose some oil capacity in the system, as the oil that cannot get sucked into the pump effectively disappears as it cannot be used...but is that it?

Thanks

[Tom Vaught]

Originally Posted by mrennie

Perhaps I am missing the obvious, but something that is fuzzy to me...

...what negative effects are there if the pickup is higher off the pan floor than ideal?

I understand that the pickup cannot be too close to the pan, or else it hinders suction and could affect flow.

But what bad happens if the pickup is say, 1" off the floor? The only thing obvious to me is that you loose some oil capacity in the system, as the oil that cannot get sucked into the pump effectively disappears as it cannot be used...but is that it?

Thanks

If the pick-up is mounted higher, as in your example, for a normal street vehicle you would never notice the difference in the extra oil below the pick-up screen.

If you are a drag racer or road racer and the pick-up is 1/2" higher vs the upper height distance, then when you accelerate (or turn corners sharply), the pick-up being slightly higher has more chance of seeing air vs oil and you would then be adding air and oil mix to your engine.

Road Race pans have trap doors to keep the oil from running away from the pump pick-up. This means the average oil level in the pan around the pick-up is higher and less chance of air entering the engine.

Some put a deflector baffle on the back wall of the oil pan (about 3 inches up) to force the oil climbing the rear wall under acceleration to turn quickly back into the sump and keep the pick-up covered.

So if you drive smoothly it makes no difference, if you drive like a NASCAR guy or a Drag Strip guy you need mods besides the stock oil pan. making sure the pick-up is about 3/8" is in the ball park for a good location but does not fix a racing oil starvation issue. Same deal for slamming on the brakes and having the oil run to the front of the pan on hard decels after the pass.

Tom V.

[lust4speed]

Another way to look at it is that 3/4" of oil (increase from 1/4" clearance to 1") the engine no longer has access to is about 8/10 of a quart. So in reality it should be the same as running the engine about a quart low on oil.

I'll add one more to Tom's list of when it might matter -- Early Edelbrock heads were notorious for holding oil up in the valve cover area, and the missing oil might be the difference between an engine that lives and one that fries the bearings - and no drag racing needed, just buzzing along at a good clip down the freeway.