High pressure vs. low pressure oil pump

[Duke W.]

Re: High pressure vs. low pressure oil pump

I think all of your questions have been answered, but their nature indicates that you don't understand the issues.

There are 3 basic small block oil pump configurations.

1. OE standard volume, standard pressure (40-45 psi)
2. OE standard volume, high pressure (55-60 psi)
3 Aftermarket HIGH volume, high pressure (as much as 80-100 psi)

Ninety nine plus percent of the 10-20 million Gen I SBs produced were built with configuration #1

The less than one percent that were built with configuration #2 consisted of '63 to '65 mechanical lifter engines and (maybe, I'm not sure) the mechanical lifter LT-1s from the seventies.

Note that configurations #1 and #2 are STANDARD VOLUME. The only difference is the relief spring value.

Configuration 3 was NEVER, EVER used in any production Gen I small block. It is strickly AFTERMARKET.

So the real question is what is the justification for installing a HIGH VOLUME, HIGH PRESSURE pump. The answer is that it was developed for loose clearanced RACING ENGINES in the sixties to maintain 80-100 psi oil pressure at very high revs - 8000 RPM or more.

Does this apply to your vintage Corvette?

Does bubba the engine builder know more than the two generations of Chevrolet engineers who oversaw the design and production of 10-20 million small blocks, some of which carried 5-year, 50K mile warranties?

Has bubba ever heard the old adage: "If it works don't fix it!"?

If you have an engine that was originally equipped with the standard volume, standard pressure pump and a 60 psi gage, use the same setup, which is most cases can be the original pump if it passes inspection and most will.

If you have a late mechanical lifter engine with an 80 psi pressue gage, use the original 55-60 psi relief spring in a STANDARD VOLUME pump, preferably the original as discussed above. The reason why Chevrolet increased the pressure on late mechanical lifter small blocks is probably lost, but my '63 L-76 survived several hundred miles of race track hot lapping shifting at 6500 with the 40-45 psi spring.

Off course, when I hot lapped Kent I ran the oil level a quart over - a trick I learned from SCCA racers to prevent oil starvation due to uncovering the pickup and sucking air.

A road engine doesn't need more volume or pressure than it was originally equpped with and installing a high volume, high pressure pump will just increase parasitic power and heat up the oil since most of it will go through the gears and be shorted back to the inlet.

These oil pump discussions are as mindless as the engine oil discussions... so-and-so said... I heard... It's 99 percent myth and misinformation!

The facts on both subjects have been laid out here and in The Corvette Restorer many times.

Duke

[Dan D.]

Re: High pressure vs. low pressure oil pump

Chevrolet built about 20 million Gen I small blocks with standard volume, standard (40-45 psi) pressure oil pumps, and this includes the high revving mechanical lifter engines through late '63. And even then for late '63 through '65 mechanical lifter small blocks got the STANDARD VOLUME pump. The only difference was they got a higher pressure relief spring - 55-60 psi rather than the "standard" 40-45 psi spring.

TWENTY MILLION ENGINES, and I have never heard of a failure due to lack of sufficient volume or pressure in any road engine, however, that doesn't include failures from oil starvation due to low oil levels while driving the car hard that essentially runs the engine out of oil. But that's not a design issue. That's an "owner is a moron" issue.

So given this track record, tell my why "bubba the engine builder" insists on a HIGH VOLUME, HIGH PRESSURE pump?

Anybody?

If you got one of these damned things and your oil pressure needle is pegged at the upper stop all the time, it will probably not do major harm - just rob some power and fuel economy and raise oil temperature a bit, but anyone who notices the gage while the engine is running will know that bubba rebuilt your enigine!

In fact, for probably about 90 percent of rebuilds, the OE oil pump is perfectly fine to reuse. Disassemble it (easy), check the gears and housing interior for damage (such as might occur if the pump ingests metal debris), check and correct, if necessary, the end clearance to about .002", and it should be good for at least the next 250K miles. Oil pumps aren't that highly loaded, and being as how they are always full of... OIL, they see very little wear in normal service.

But "bubba the engine builder" would rather sell you a new high volume, high pressure oil pump (and get the markup on the part) - "because that's what all the racers use" - than spend ten or fifteen minutes inspecting the original.

And remember that some of the new castings are weaker than OE and have been know to fracture. The OE castings that have been in service for 30 -60 years don't break unless something has disintegrated inside the engine and been ingested by the oil pump or someone hits them dead center with a full blow from a sledge hammer.

Duke

Hi Duke, I think Bubba Builders just kind of automatically install new oil pumps in the engines they rebuild. And regardless of whomever they buy their pumps from, it is most likely going to be a standard offering Mellon M55. They seem to to have the market on oil pumps these days. Why engine builders just tend to install new pumps, I don't know.

When I told my engine shop about the wimpy Mellon pump, his response was "We have probably sold 500 of these pumps and never had a compliant". This particular shop is well known in the area and has a good reputation. I like them and I trust them. They specialize in SB Chevy's, and they do a lot of marine engines as well. The shop took back my M55, got me a good pump, set the pickup position in the pan, and tack welded it in place for me. I have no complaints. Only that I had to pull my oil pan while in the car, and change all this stuff over. But I am glad I did, and I do agree with you on this matter, and I take your advice very seriously as well.

I think a better question is why does Mellon continue to produce this crappy pump, and why do they install a medium pressure spring, and give you a high pressure one in the box? If you want low pressure, you have to call them and beg them for it. Another point is the standard M55, while it is higher pressure than OE, is standard volume, at least so they say.

And finally Duke, I think this low pressure requirement originated from you, and on this forum. So I don't think it is widely known outside of NCRS. I know my shop did not know the M55 had a smaller, weaker casting. One other question is why did GM change to a higher pressure pump for solid lifter engines in 1963? Do you think there was a problem?

Regards, Dan

[Duke W.]

Re: High pressure vs. low pressure oil pump

And finally Duke, I think this low pressure requirement originated from you, and on this forum. So I don't think it is widely known outside of NCRS. I know my shop did not know the M55 had a smaller, weaker casting. One other question is why did GM change to a higher pressure pump for solid lifter engines in 1963? Do you think there was a problem?

Regards, Dan

I don't set oil pressure requirements. I have merely reminded TDB members what the OE requirments are as established by Chevrolet engineering decades ago, and they are all in the appropriate year AMA specs.

The appropriate question is why do all these "engine builders" install pumps that don't meet OE requirements? As I have said time and time again, the OE oil pump in your engine, if it's still there, is your best choice if it passes a simple inspection.

Regarding your last two questions, I answered them in my previous post. In short, I don't know, and I'm sure the ECR that requested the change and had the reason is long gone, but 40-45 psi never hurt my L-76 despite being run hard many, many times.

The key is to keep the oil level near the full level, and even run up to a quart over if you plan on jazzing the car around alot so the pickup doesn't get uncovered.

Modern NASCAR engines run 20-30 psi at 9500 revs with 0W-20 oil. A lot of "common knowledge" has changed in the last four decades.

Duke

[Michael H.]

Re: High pressure vs. low pressure oil pump

The key is to keep the oil level near the full level, and even run up to a quart over if you plan on jazzing the car around alot so the pickup doesn't get uncovered.


Duke

Yup, I agree. I've built and raced a LOT of small and big block engines decades ago and I've never had an oil related issue. I've driven cars with small and big blocks for almost five decades and never had any oil pump/supply related issues. (other than a few that I caused because I did something stupid) We ran the small block Z28 one quart over full. Never an issue. (GM told us we could use as much as TWO quarts over for Trans-Am racing with the original Z28 oil pan)

I always reinstalled a high pressure pump in engines that were originally equipped that way though.

I think the high pressure pump that GM installed in early solid lifter Corvettes was just a bit of in insurance for them and the owner. It would be the same as the big 8" balancer for HP small blocks. It wasn't needed for 98% of the new Corvettes sold every year but it was there in case an owner decided to seriously race the car.

[Steven G.]

Re: High pressure vs. low pressure oil pump

30-40 +- years ago I sold many HV/HP oil pumps in a speed shop I once owned. I recall some reasons why customers wanted these pumps. Most of the time they were doing a rebuild and some slightly worn crankshafts were reinstalled thinking a HV pump may help the loose crankshaft clearance, seeing good oil pressure at idle on a hot day was very appealing at that time as well, some believed the crank would actually have less friction during rotation. I know the factor pump can last hundreds of thousands of miles without a problem, there are still old rebuilt engines that used HV pumps at that time that are alive and well today. To each their own opinion but if it an't broke why fix it, wait until the next rebuild and use a factory spec. pump, be sure to check wear and all clearances at that time. That is just my opinion. Steve

[Duke W.]

Re: High pressure vs. low pressure oil pump

Vegas had a reputation for oil starvation, so I usually ran my Cosworth Vega one-half to one quart over full in track events and never had an oil pump/pressure related problem in 5000 miles of hot lapping Riverside and Willow Springs.

BUT, the full length baffle between the pan and the block was a problem. This baffle fractured TWICE at the weld nuts that hold the pickup tube support resulting in the pickup breaking off the end of the tube. I knew there was a problem when the oil pressure dropped under braking! After the second failure I had the used baffle I acquired reinforced with a TIG weld fillet at the weld nuts and then stress relieved in a high temperature oven.

Of course, this problem had nothing to do with the oil pump or pressure. It was a mechanical problem due to the second order unbalanced vertical shaking force in four-cylinder engines without balance shafts that caused fatigue failure of the weld nut joint. The TIG weld fillet spread out the load, and the oven baking relieved the residual welding stress.

An old mechanic told me in the seventies that the early Vegas, which had lower ride height than the later model years had a reputation for bearing problems. Bottoming the car could push the pan into the oil pickup causing oil starvation, and he could always tell from the telltale pushed up oil pan bottom.

Most guys, including bubba the engine builder think that if you have an oiling problem it's the "oil pump". A little engineering intuition and some forensic investigation usually shows that it's something other than an oil pump or oil pressure problem; 99 percent of the time it's an oil starvation problem.

There's a reason why the highest performance modern Corvettes than can generate 1+g cornering and braking forces have dry sump oiling systems.

BTW the full length Vega oil pan baffle was not a "high performance" part. It was there to enable the Vertipak shipping method where the cars we loaded into rail cars one end, nose down. The baffle was needed to prevent the oil flooding the front of the engine and running out the crank and cam seals.

Duke

[Duke W.]

Re: High pressure vs. low pressure oil pump

30-40 +- years ago I sold many HV/HP oil pumps in a speed shop I once owned. I recall some reasons why customers wanted these pumps. Most of the time they were doing a rebuild and some slightly worn crankshafts were reinstalled thinking a HV pump may help the loose crankshaft clearance, seeing good oil pressure at idle on a hot day was very appealing at that time as well, some believed the crank would actually have less friction during rotation. I know the factor pump can last hundreds of thousands of miles without a problem, there are still old rebuilt engines that used HV pumps at that time that are alive and well today. To each their own opinion but if it an't broke why fix it, wait until the next rebuild and use a factory spec. pump, be sure to check wear and all clearances at that time. That is just my opinion. Steve

It's amazing what some people are willing to believe. When I disassembled my '63 L-76 (with a 40-45 psi oil pressure relief spring) at 115K miles, which had been run hard and put away wet numerous times, the crank miced out right in the middle of the OE tolerance range, and the Moraine 400 bearings were reuseable. (But I did replace them - with new Moraine 400 from GM.)

Oh, and I disassembled/inspected the oil pump. It looked like new inside. The only thing I did was a little wet sanding with 400 paper on a piece of glass of the end cover and one gear to get about .002" end play on both gears. I reinstalled it, and it's still there, today.

I thought about installing the higher pressure spring from the late mechanical lifter engines, but given the condition of the engine, I decided it wasn't necessary.

Duke

[Loren L.]

Re: High pressure vs. low pressure oil pump

In my wildest dreams, I don't think ANYONE involved in this prior discussion was thinking/worrying about Vegas. I don't have a horse in this rat race - and will continue to use high volume/pressure oil pumps in any solid lifter SBC that is mine, but I will refer you to the July 1965 Chevrolet Service News, on page 6, where the entire item reads:

"High Engine Oil Pressure!
Corvette 327 cu. in. - 365-375 HP

The above 327 cu. in. high performance Corvette
engine oil pressures in the area of 80-95 psi (at 2,000
RPM can be expected and are perfectly normal. However,
damage may occur to this engine if the 283 cu. in. engine
oil pump is used which delivers oil pressure of 65 psi at
2,000 RPM."

[Duke W.]

Re: High pressure vs. low pressure oil pump

The OP was talking about a 300 HP engine.

As I said, my '63 340 HP engine never suffered any issues with the standard pressure oil pump. The extremely high oil pressures listed in the TSB would probably only be evident at very cold starting temperatures with oil viscosities that were too high for the ambient temperature - like straight SAE 30 at below freezing temperatures.

If the earlier Duntov-cammed engines needed higher oil pressure, they would have implemented the higher pressure relief spring years earlier. Maybe the 30-30 cam needed more oil pressure. Yeah, right! Why didn't they recall all the earlier mechanical lifter engines to install a higher pressure relief spring?

Some TSBs need to be taken with a grain of salt. This one clearly has some holes talking about using a "283 oil pump" in a 365/375 HP engine. What about the '62/ early '63 40-45 psi oil pump that was used in mechanical lifter 327s. It was the same as earlier 283s. Would it destroy a 365/375 HP engine? I seriously doubt it.

Owners often complain about "high" or "low" oil pressures - same with engine temperatures. Some OEMs eliminated the "problem" by replacing calibrated gages with idiot lights that rarely turned on.

Problem solved!

As far as Vega/Cosworth Vega engines are concerned they have similar issues - as do most engines of the era - so lessons can be learned - like don't let your oil level get low and don't bottom out the oil pan.

Duke

[Timothy B.]

Re: High pressure vs. low pressure oil pump

I can only speculate that the higher 60lb oil pressure on the mechanical lifter small blocks is used to keep a good oil film on the main/rod bearings at the higher RPM's of the engine. Along with this, the edge orifice lifters are used to limit this extra oil to the top of the engine.

[John H.]

Re: High pressure vs. low pressure oil pump

I think a better question is why does Mellon continue to produce this crappy pump, and why do they install a medium pressure spring, and give you a high pressure one in the box?

Dan -

Probably because GM (re-)designed it as part of their failed "mass reduction" program, and Melling was the supplier of that pump to GM for many years after GM stopped making oil pumps in-house at the engine plants. GM said "here's what we want you to make", and Melling did just that. GM obviously didn't include extreme high-performance usage in their durability validation program for the redesigned lightweight pump, and when reports started coming back to Melling on casting failures for the "new" pump they sold in their wholesale channel, suddenly the "old" pump reappeared as the "Select 10553" pump that Melling sells today. They still sell the GM-redesigned M55 pump with the weak casting, but it includes a warning card in the box that doesn't recommend it for high-performance applications.

[Duke W.]

Re: High pressure vs. low pressure oil pump

I think a used vintage pump that passes visual inspection and is reworked as necessary (it doesn't take long) to achieve .002" gear end play is the best option and it costs nothing if you still have the OE pump and it hasn't ingested a bunch of metal debris.

I think Dom said earlier that he has a bunch of used pumps.

Duke

[Dan D.]

Re: High pressure vs. low pressure oil pump

Dan -

Probably because GM (re-)designed it as part of their failed "mass reduction" program, and Melling was the supplier of that pump to GM for many years after GM stopped making oil pumps in-house at the engine plants. GM said "here's what we want you to make", and Melling did just that. GM obviously didn't include extreme high-performance usage in their durability validation program for the redesigned lightweight pump, and when reports started coming back to Melling on casting failures for the "new" pump they sold in their wholesale channel, suddenly the "old" pump reappeared as the "Select 10553" pump that Melling sells today. They still sell the GM-redesigned M55 pump with the weak casting, but it includes a warning card in the box that doesn't recommend it for high-performance applications.

Makes sense John. But it still does not explain the medium and high pressure spring configuration. It seems to me they should supply the low and medium pressure springs - not the medium and high.
And at this point in time they could discontinue the M55 and just offer the 10553. They get considerable more money for the 10553, but it can't cost more than a few pennies difference to make. -Dan-

[Timothy B.]

Re: High pressure vs. low pressure oil pump

Dan,

Melling makes oil pumps for many applications as well as other engine parts, I think the pumps are top of the line FWIW.

After speaking to a Melling tech on the phone he stated the pressure issue comes up with restorers so I assume it's not really a big deal to them. I agree with you about the supplied relief springs that come with the pump, you would think there 49psi spring would be the standard.

[Tom P.]

Re: High pressure vs. low pressure oil pump

I don't want to get too deep into this dogfight, but I will add some personal experiences from the past 50+yrs of building/running Chevy V8 engines (prior to that, it was hotwater babbit beaters).
I have used HP pumps in every V8 that I've ever built/driven with Zero issues. Some were stock pumps with a Chevy HP spring installed.
The last engine that I replaced was a 350 from my 51 Chevy that I built 35yrs ago/300Kmi ago. It was still running. Once it was thoroughly heated up and normalized, the oil pressure was 60psi (80 when cold). When I pulled the engine 2mo ago, it was doing good to hold 35psi (LOTS of bearing clearance ). I replaced that very tired 350 with a built 383 and stuck that pump right back in the 383. All I did to the pump was run clean solvent from my parts washer through it, blow it out and oiled it before installing it in the 383. I also replaced the cracked plastic connector on the shaft. Now, after the 383 is heated up, oil pressure is about 55psi. That 383 is soooooooooooo much nicer than the tired 350!
The SB400 that is in the 56 has a HP pump--------------and the original, stock 56 oil gauge. When cold, the gauge is hard pegged! After thoroughly heated up, it stays at about 55psi (it also has a Chevy HP spring in the pump). Again, zero ill effects.
If HP oil pumps are detrimental to an engine, including a lo-perf daily driver engines, I've never experienced any problems. Thus, since nothing has ever broken as a result of a HP pump, I'm not fixing it.