BB - Replace high pressure oil pump?

[Joe L.]

Re: BB - Replace high pressure oil pump?

I talked to my machinist again about this today. I may just manage to beat him to death with oil pump questions yet. He said he put a Melling pump in it with the 427 performance spring that was called out. He will have to do some digging to come up with part numbers. He is guessing that it will have 50 - 60 PSI with the engine warmed up at cruising RPM. Does that tell you experts anything useful?

Joe

Joe----


Yes, that's just about the pressure I'd expect IF the Melling SHP pressure relief spring is comparable to the GM SHP relief spring.

[Joe L.]

Re: BB - Replace high pressure oil pump?

If all things are correct (bearing clearances), a small block or big block do not need any additional pressure or volume. I just completed a 427-400 hp last year and the engine builder INSISTED on a high volume pump. Guess what, too much oil pressure. 50-55lbs @ idle warm with 5w30 Mobil 1. This is a car that won't be judged so I am not going to tear back into it. If you seek my advice......stock pump!

tim

tim-----


I don't understand that. A high volume pump should use the same pressure relief spring as a standard volume pump. In any event, the GM standard volume SHP pump (i.e. L-71, L-88) uses the same pressure relief spring as the high volume ZL-1 pump.

Incidentally, though, your application did not originally use a pump with high pressure spring. All L-68 used the standard pressure spring.

[Tim S.]

Re: BB - Replace high pressure oil pump?

Joe,
I must admit to this day, I do not know what pump in particular that I have. The biggest reason I injected my opinion to this thread was due to the fact that Joe is considering the PV process some day. Obviously, you have an understanding and knowledge that most of us seek at a time like this. Very valuable I might add!

Tim

[Joe R.]

Re: BB - Replace high pressure oil pump?

Joe,

I'm not sure I understand your reply. Are you saying that I don't need to bother with replacing the pump?

Thanks,
Joe

[Joe L.]

Re: BB - Replace high pressure oil pump?

Joe,

I'm not sure I understand your reply. Are you saying that I don't need to bother with replacing the pump?

Thanks,
Joe

Joe-----


I don't understand what gave you the idea that I am suggesting that you not replace the pump? Are we talking about the original pump, the replacement the shop installed, or something else?

[Joe R.]

Re: BB - Replace high pressure oil pump?

Joe,

Let me try the question another way. Do you think the Melling pump that is in it with the 427 performance spring will be fine or should I go with the ZL1 pump you mentioned?

Joe

[Joe L.]

Re: BB - Replace high pressure oil pump?

Joe,

Let me try the question another way. Do you think the Melling pump that is in it with the 427 performance spring will be fine or should I go with the ZL1 pump you mentioned?

Joe

Joe-----


I would say the Melling pump is fine. In fact, Melling now manufactures a great many of the oil pumps for the OEM's, including GM. Of course, that does not mean that they make their aftermarket pumps exactly the same as the OEM pumps. However, Melling is a quality brand and I've used them in the past with no problem.

The only problem I see now are these various reports I've heard of what seems to be abnormally high oil pressure. I don't understand that. However, it's possible that the Melling-supplied "performance" relief spring is too stiff. The original GM spring for SHP engines was 5/16" OD, 2-7/16" OL, and 24 coils. You might want to compare that with what you have in this pump. That will not guarantee that the springs are the same rate even if they are the same in these respects, but it will "hint" at it.

[Joe R.]

Re: BB - Replace high pressure oil pump?

Joe,

I talked with my machinist again. He said that he put a 60 psi spring in the oil pump. He also mentioned that the stock spring gives 52 psi.

Joe

[Joe R.]

Re: BB - Replace high pressure oil pump?

Joe,

Here's the to do list!

1. Remove the potential POS pump that your machinist installed!
2. Go to Chevrolet and purchase the 3969870 pump that Joe L. recommended!
3. Live happily ever after!

JR

[Duke W.]

Re: BB - Replace high pressure oil pump?

Here's a basic Hydraulics 101 review of oil pumps.

Gear type oil pumps are an example of constant volume design. If we dump the output into a bucket, the rate of volume delivery in, say, gallons per minute is approximately linearly proportional to pump speed to the point of cavitation.

If we place a restriction in the output line - equivalent to the engine restriction due to bearing and other internal clearances - the pump will build pressure as speed increases, and the higher the pump's delivery volume, the faster the pressure will rise.

This is where the pressure relief spring/valve comes into play. Once the relief valve opens, output pressure remains constant, excess output oil is short circuited back to the input side, and oil delivery volume and pressure to the main oil gallery remain nearly constant up to peak revs.

With the same relief spring a "high volume" pump should achieve relief spring pressue at lower speed, but it will consume more power than a standard volume pump.

Since these gear pumps have constant volume delivery characteristics a "high volume" pump will be physically larger. The gears will either be longer of larger in diameter, or both relative to a "standard volume" pump.

Because many racing engines based on SB or BB Chevies have "loose" bearing clearances, a "high volume" pump has traditionally been used to achieve the desired 80-100 psi at very high revs, but this is not necessary for a road engine, so all a high volume pump will do is increase parasitic power loss churning up the oil.

Also, if the engine has typical OE bearing clearances, the oil volume delivery may overwhelm the bypass, so delivery pressure keeps rising even if the bypass valve is full open.

There seems to be a problem distinguishing between Melling's OE replacement and "hot rod" pumps, so my recommendation is to buy a Sealed Power OE replacement pump, and you can look up the number and specs at napaonline.com. As is the case with so many GM and aftermarket OE replacement parts, the source of what's inside the box is often the same regardless of the brand name on the box.

You also have to overcome the moronic "engine builder mentality" that says you need a "high volume" pump in an OE rebuild or mildly modified OE engine that will only see road use or "light racing". If the guy stands fast on this issue, you should take your work elsewhere. You will probably also get too low compression and a camshaft with too much overlap and end up with a poor performing, gas guzzling engine relative to the OE configuration.

Beyond this, most original oil pumps probably don't need to be replaced, and various books like "How to Hot Rod..." explain how to inspect and blueprint the pump. Oil pumps are very simple devices and unless the pump ingests some serious debris, they virtually never "wear out".

Look up the hot oil pressure spec for you engine in the AMA specs, and as a general rule you can assume that it's 40-45 psi if the configuration included a 60 psi dash gage and 55-60 if equipped with a 80 psi dash gage.

As an interesting side note, it's my understanding that 9000+ rev unrestricted NASCAR engines only run about 30-40 psi oil pressure (and 5W-20 oil for the race, 0W for qualifying). Why? ...to reduce parasitic power loss to a minimum (same applies to the coolant pump), so by analysis and experiment they have found the minimum volume/pressure and oil viscosity that will allow the engine to live, and this will allow the engine to deliver more useable power to the flywheel and get better fuel mileage!

Duke

[Bill C.]

Re: BB - Replace high pressure oil pump?

A very thought provocative post !

I have to change my pump to pass PV - mine is a Melling M77HV with a standard pressure spring. This is my winter project before Kissimmee.

[Tim S.]

Re: BB - Replace high pressure oil pump?

I would be careful about the napaonline.com information. Reason being, recently, NAPA changed to Sealed Power from Melling for oil pumps and several of the slower moving numbers ( I think a BB Chev would qualify as a slow mover today) are nothing more than reboxed or relabled. Hence, really nothing to gain. I own a couple of NAPA stores and I have been down this same road before during manufacturer changes. If you would go to your local NAPA store, just insist on a pump being ordered directly from Sealed Power rather than inventory from one of the local distribution centers. If you would be inclined to order a pump from napaonline.com, you will get a pump from a distribution center rather than Sealed Power.

I agree with Duke in his thoughts. It is good advice.

Tim

[Ray G.]

Re: BB - Replace high pressure oil pump?

Hello Duke;

Educational reading your detailed explanations.

We have built many 100s street engines.
Always used "original stock" style pumps.
Bearing fits are crucial.
No failures, yet.

Be safe.
Ray

[Clem Z.]

Re: BB - Replace high pressure oil pump?

i had a BBC 600 HP race engine run a 150 mile race with just with 30# of oil pressure due to a pressure relief valve problem and the engine showed no damage from low oil pressure.

[Joe R.]

Re: BB - Replace high pressure oil pump?

All,

Thanks for the advice. I was hesitant to pull the pan and pump because my time to work on the car is very limited. But I have decided that it is better to do the job right the first time. I have ordered the GM 3969870 pump from my friendly local Chevy dealer.

My next question is, what do you guys recommend using for the oil pan gasket?

Thanks in advance,
Joe