[Ted's37]

I have a 327 SBC. How much clearance do I need from the oil pump pick up screen and the bottom of the oil pan. I have about 1/4". Is that enough.
Thanks for any reply's

[bigdog7373]

You should have at least the diameter of the pickup tube. I don't believe 1/4" is enough. That seems really close.

[MouseFink]

Yes, 1/4" is too close. The tight clearance will cause a vortex to form under the pick up screen and that will cause the intake screen to pick up a reduced amount of oil at higher RPM.

You must be using an aftermarket SB Chevy oil pump with a 3/4" pick up tube. A SBC oil pump with a 3/4" pick up tube is closer to the bottom of the oil pan because it has a thicker bottom plate to accomodate the larger pick up tube. That is why the factory always used standard SB Chevy oil pumps with a 5/8" pick up tube. The factory started using a 3/4" pick up tube on the oil pumps in 1992 along with a redesigned oil pan.

[cdminter59]

There is suppose to be about 3/8" clearance between the pickup and the oil pan. If there is not enough clearance take some measurements using the oil pan rail to the oil pump pickup. Then measure the same measurements from inside the oil pan using the flange of the oil pan. once you find the exact location of the pickup beat the bottom of the pan outward. Beats buying a new oil pump or pickup which it sounds like somebody bought the wrong pickup for the type oil pan you have.

[Ted's37]

It is a high volume oil pump with the rectangular screen on the pick up. It measures 2 3/4" X 1 1/2". The pick up tube is 5/8" in diameter. My old oil pan was 7 5/8". My new pan is 7 1/2" deep. I had no trouble with the old pan other then it looked like crap. I guess my question now is, is a stock oil pump shorter then a high volume pump?

[MouseFink]

Yes. A Melling Select high volume oil pump has a 3/4" pick up tube and the housing and bottom plate is .500" (.487") longer than a GM high pressure oil pump with a 5/8" pick up tube. GM does not offer a high volume oil pump for a SBC. People get confused and think they have a high volume oil pump if it has a 3/4" pick up tube.

If you buy a aftermarket custom pick up assembly, there is no predicting what clearance you will have, as you found out. Achieving the correct oil pan clearance with a custom pick up will be a crap shoot, unless you make it yourself. I tried one Moroso and two Milodon pick up assemblies. I thought about buying a custom made Kevko pick up assembly that I thought would fit my pan with 3/8" - 1/2" bottom clearance and decided to modify the stock pick up myself and add a JEGS pick up brace. I got a perfect fit.

Moroso and Milodon offers a oil pump and pick up kit and you are more likely to get a good fit with the kit.

[cobalt327]

Originally Posted by Ted's37

It is a high volume oil pump with the rectangular screen on the pick up. It measures 2 3/4" X 1 1/2". The pick up tube is 5/8" in diameter. My old oil pan was 7 5/8". My new pan is 7 1/2" deep. I had no trouble with the old pan other then it looked like crap. I guess my question now is, is a stock oil pump shorter then a high volume pump?

First, be sure the oil pan you have now hasn't had the bottom dented upwards in shipping.

Also, unless you have a legit need for a high volume pump, you should use a standard volume pump. Using a standard pump will add to the amount of clearance you have between the P-U and pan bottom.

The idea in using a deep pan is to reduce windage, so don't fill the deep pan to the same level as it was w/the stock pan.

[ap72]

Originally Posted by cobalt327

First, be sure the oil pan you have now hasn't had the bottom dented upwards in shipping.

Also, unless you have a legit need for a high volume pump, you should use a standard volume pump. Using a standard pump will add to the amount of clearance you have between the P-U and pan bottom.

The idea in using a deep pan is to reduce windage, so don't fill the deep pan to the same level as it was w/the stock pan.

why use a std. volume pump? I always use a hv pump on any street engine I build if the option is available. It may not be needed but its good insurance and insures adequate flow at low rpm, at mid to upper rpms there is nothing to be gained and it can increase aeration of the oil from it circulating through the bypass BUT on a street engine that is usually not the case.

On my Nissan L28 the idle pressure went from about 5psi to 40psi when I swapped to a HV pump- like I said just insurance everything is properly oiled at low rpm.

Also, the stock melling M155 pump has the preferred 3/4" pickup for the sbc, as said it was used on the later model sbc's and lt1's. M155hv is the high volume unit.

There are also some gains to be had from porting the pump and the rear main cap it bolts to- don't take off to much just smooth it out to reduce aeration, cavitation, and dynamic pressure loss. If you want to really go overkill you can also enlarge the oil mains in the block.

[cobalt327]

If the pump is adequate at a normal volume, use it. If you need more volume for a reason, then use it. But not because you think it's "insurance" against... what?

[ap72]

Originally Posted by cobalt327

If the pump is adequate at a normal volume, use it. If you need more volume for a reason, then use it. But not because you think it's "insurance" against... what?

inadequate oil flow at low rpm

Once you hit the max operating pressure the bypass opens and it wont flow a drop more than a std volume pump, but at low rpm you will have more flow and pressure throughout the engine.

Now a high pressure pump is a different animal, and I have never used a high pressure pump- don't see a need for that.

[cobalt327]

Dude. If you are internally losing so much oil at low rpm that you need a HV pump then you either have uber wide bearing clearances or more problems than a HV pump will "cure".

But hell, YOU can do what you want- just don't advise anyone else do it w/o a reason.

Edit- is that how you design your **** pumps? Build it w/too much volume "just in case", and just let it bypass all the time?

[MouseFink]

Originally Posted by ap72

why use a std. volume pump? I always use a hv pump on any street engine I build if the option is available. It may not be needed but its good insurance and insures adequate flow at low rpm, at mid to upper rpms there is nothing to be gained and it can increase aeration of the oil from it circulating through the bypass BUT on a street engine that is usually not the case.

On my Nissan L28 the idle pressure went from about 5psi to 40psi when I swapped to a HV pump- like I said just insurance everything is properly oiled at low rpm.

Also, the stock melling M155 pump has the preferred 3/4" pickup for the sbc, as said it was used on the later model sbc's and lt1's. M155hv is the high volume unit.

There are also some gains to be had from porting the pump and the rear main cap it bolts to- don't take off to much just smooth it out to reduce aeration, cavitation, and dynamic pressure loss. If you want to really go overkill you can also enlarge the oil mains in the block.

What is the GM part number for a high volume oil pump?

Melling offers all kinds of oil pumps for SB Chevy engines but GM only offers a high pressure and a standard pressure oil pump in a standard volume housing. Just because a SB Chevy oil pump has a 3/4" pick up tube does not mean it is a high volume oil pump. GM started offering oil pumps with a 3/4" pick up tube in 1992 for engines with oil coolers and remote oil filters. In addition, they offered a 21 PSID by-pass valve as a service replacement for the OE 11 PSID by-pass valve. It was an effort to prevent warranty problems due to bearing failures in engines with remote oil filters and oil coolers.

GM realized they had a problem with the extra plumbing with a remote oil filter and oil cooler so they introduced the oil pump with a 3/4" pick up tube. GM still used the standard volume oil pump with a 3/4" pick up tube due to the lack of adequate oil pan clearance. If you have an engine with a remote oil filer and/or a oil cooler, it would be a good idea to purchase and install a Melling Select 10552 or a Melling M155 high volume oil pump and use a 21 PSID by-pass valve at the first engine rebuild.

[ap72]

Originally Posted by cobalt327

Dude. If you are internally losing so much oil at low rpm that you need a HV pump then you either have uber wide bearing clearances or more problems than a HV pump will "cure".

But hell, YOU can do what you want- just don't advise anyone else do it w/o a reason.

Edit- is that how you design your **** pumps? Build it w/too much volume "just in case", and just let it bypass all the time?

actually as a general rule you do ALWAYS run a larger than required pump on the projects I deal with, for 2 reasons- planning for any changes that may happen down the road, and it prevents over cycling, meaning the pumps will just be turned off more than they are on and that greatly improves service life. But those aren't oil pumps.

Since you probably never worked with an L28 you may not know this but they are NOTORIOUS for low oil pressure from the factory, I forget which engine exactly but I believe I scavenged a pump off a KA24 for the L28 (could be wrong though on the engine model though). The L28ET and diesel version both have upgraded oil pumps, but I went a little further with mine.

As for oil pressure at idle- look at what the newer designed engines are running at hot idle, and look at what most original sbc's are running at hot idle... The extra flow at idle won't hurt a damn thing but it can help a lot.


Also, while the 3/4" pickup isn't necessarily a HV pump (M155 vs M155HV) the 3/4" pickup is used to prevent cavitation, and again using a larger pickup won't hurt a damn thing and can help a lot.


With all of the added benefits and no real draw back (besides high RPM aeration through the bypass) I can't see why anyone would use anything other than a M155HV style of pump on the street.

[cobalt327]

I forget, which is it, a troll or flamer that posts things just to cause an argument?

Oil aeration happens any time a pump bypasses. At low speeds this is probably not going to be a big problem, but less is always going to be better than more, providing the oil pressure requirements are met.

I know there are people who say they will put up w/the aeration, oil heating and power drain caused by a high volume pump- they also require the engine owner to run an oil cooler to offset this. Now, why they like to see 45 psi at hot idle, I will leave that to them to explain.

Other pro engine builders like CNCNE use a standard volume pump on "99%" of their street performance engines, presumably w/o failures caused by this practice.

MY bottom line is- again- run only as much pump as is needed. No more. No less. In my experience, this means a std. volume pump for the vast majority of engines. I also block off the filter mount bypass (if present), and have never had a failure using a standard volume pump. EVER! And you need to remember- I have actually built engines. Real ones. Lots of them, too.

But hey- don't listen to me. Here's a thread, has posts by some guys who also actually build engines: std vs high volume oil pump controversy • Speed Talk