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  #31 (permalink)  
Old 03-18-2011, 05:24 PM
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Explanation of cavitaion for the "Shade Tree" mechanic.

I purchased my #23620 and used it on a 3/4" inlet tube by welding it. Since I purchase it from Jegs, I assumed Summit had it also. Summit usually has everything Jegs has, only a little cheaper.

CAViTAION - Quote Mike Osterhaus of Melling oil pumps, Jackson MI:

"Cavitation typically occurs with a SB Chevy oil pump about 4,500 RPM, causing the pump's output to flatline regardless of how much faster the engine revs. This can cause a dangerous drop in oil pressure just when the engine needs more oil, not less. Stock oil pumps are made for engines that spend most of their time below 3,000 RPM. They have problems with cavitaton and oil pressure loss at high RPM."

"Cavitation is a function of inlet design of an oil pump. The point at which cavitation occurs depends on the pump speed and the size of the inlet tube." says Osterhaus. "Up until the early 1990s, Chevrolet used a 5/8" pickup tube on it's V8 engines. In 1993, Chevy changed to a larger 3/4" inlet tube that flows better with reduced cavitation. We still make the M55 oil pump for the older applications, but recommend the newer M155 pump with the 3/4" inlet as a retrofit for better flow."

I used a copper gasket between the block and the Melling Select 10552 oil pump to better mate the machined surfaces when using a high volume or high pressure oil pump. Melling pickup assemblies use a inlet tube which is cut at an oblique angle inside the screen which also reduces cavitation up to 8,000 RPM.

A high volume oil pump is not required if the engine clearances are stock. However, if you have a remote oil filter and oil cooler, a high volume pump should be considered.

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  #32 (permalink)  
Old 03-18-2011, 05:30 PM
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I dont like to disagree with an engineer, but I have built and raced hundreds of SBC with stock and high volume pumps, some running up to 8500RPM, with no issues with oil pressure dropping or oil starvation.
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  #33 (permalink)  
Old 03-18-2011, 06:03 PM
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thank you for the answers guys.
I guess that try the pressure with a mechanical gauge is important then i'm tempted to try the oil pump mods to prevent cavitation, i have a new pump on the shelf so let's try.
i have brazed the pick up so there's no way to suck air from that and yes, the plug in the oil pump cover is ok, i remember to have seen it when i had to take out the spring before the brazing.
Bogie was talking about something wrong on the distributor, well i've made the groove on it to help lubrication on the gear... any suggestion?
About high volume or high pressure pumps? No way, i'm sorry but i don't want to trash distr. and cam on a stock clearances engine.
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  #34 (permalink)  
Old 03-18-2011, 06:18 PM
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Sorry, I do not see any documented evidence. What I do see is an anecdote from a person who makes a product to replace a stock component. Hardly un-biased. Millions of small block chevys have run over 3000 RPM with no cavitation.

Again, one more time, slap a high volume pump in like the one GM put in their STOCK engines with NO problems despite the engines being built with STOCK clearances.
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  #35 (permalink)  
Old 03-18-2011, 07:17 PM
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HV pump... not

FYI.. GM never equipped SB Chevrolet engines with a HV oil pump until 1993. From 1962 until it was discontinued, if you wanted a HV pump for your SB Chevy engine, you had to install a 409 Chevy oil pump. Finally in 1993, SB Chevy V8 and V6 oil pumps were redesigned for a 3/4" inlet tube but that did not make it a HV pump. For a passenger car that is driven below 3,000 RPM most of the time so not being a HV oil pump does not present a problem. An aftermarket HV pump with longer spur gears will not fit inside a stock oil pan because a SB Chevy pick up assembly will hit the botom of a stock SB Chevy oil pan.

In 1993, GM equipped their stock volume SB Chevy oil pumps with a 3/4" inlet tube in order to reduce cavitation and for no other reason. That is because the Melling engineers informed GM that above 4,000 RPM, the oil pump spur gears will cavitate the oil when using a 5/8" inlet tube. At high RPM, the spur gears was pulling oil through a inlet tube that was too small to fill the cavities between the gears. That condition causes the spur gears to cavitate (foam) the oil. The size of the inlet tube is the only difference between the early GM / Melling M55 oil pump and late GM / Melling M155 oil pump. Both pumps are rated at standard volume but the latter oil pump with the 3/4" inlet does not cavitate the oil as bad.

Last edited by MouseFink; 03-18-2011 at 07:27 PM. Reason: typo
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  #36 (permalink)  
Old 03-19-2011, 08:11 AM
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Actually, the oil pump that GM put in the DZ 302 was a standard pump fitted with a "pink" sprine making it a high pressure pump. Many sites have it listed as either a high volume or high pressure pump. THE POINT OF THIS is, you can run a non-stock pump in an engine with stock clearances just like the factory did. I'm done, I've been running a high volume oil pump in my 350 for 25 years now with no problems. Just like thousands of other rodders.
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  #37 (permalink)  
Old 03-19-2011, 09:04 AM
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Imformation for the SB V8 engines

As I mentioned before, I used a Melling Select 10552 (+10%) HV / std. pressure oil pump in my S10 4x4 with a stock 9-1/4" deep pan. That oil pump has the option of a bolt on pick up or pressed in pick up. I had to use a stock 3/4" pressed in pickup by shortening it by 1/2" in order to fit the stock Chevy V6 4x4 oil pan with 1/2" bottom clearance.

My machinst and I discussed fitting the HV oil pump in a Chevy V8 engine last night and he said the Melling Select 10552 (+10%) HV/std. pressure oil pump can use a optional Melling 12559 bolt on pick up and it will fit in a stock SB Chevy V8 oil pan. Melling apparently recognized the problem fitting their HV pumps in a stock SB Chevy oil pans and they made a shorter bolt on pickup that will fit correctly in a stock SB Chevy V8 oil pan. IMO, the bolt on pickups can still break at the 2-bolt flange and fall off. That is because the Melling bolt on pickups do not press into the pump housing. I don't trust a bolt on pickup and would never use one on a SB Chevy V8 engine unless it was welded to the 2-bolt flange more solidly than they appear to be. The Melling pickup flange to pump mounting requires a special gasket and that is a source of a leak or failure.

However, IMO, a Melling +25% higher volume Melling Select oil pump should never be used with a stock volume oil pan. The Melling (+25%) HV oil pumps are considered racing oil pumps for engines with wider bearing clearances. A standard volume oil pump and a stock volume oil pan should never be used for racing even though some claim to be able to get away with it.

Last edited by MouseFink; 03-19-2011 at 09:15 AM.
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  #38 (permalink)  
Old 03-19-2011, 09:49 AM
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Quote:
Originally Posted by MouseFink
...a Melling +25% higher volume Melling Select oil pump should never be used with a stock volume oil pan. The Melling (+25%) HV oil pumps are considered racing oil pumps for engines with wider bearing clearances.
Why? Please tell me it's because "it'll suck the pan dry!"
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  #39 (permalink)  
Old 03-19-2011, 11:31 AM
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pan volume

I never said a HV pump can "suck a pan dry" although it is possible.

The theory is that at a sustained engine speed above 4500 RPM, the engine has about 3-1/2 quarts flowing through it. If your oil pan only has 4-1/2 quarts to begin with, the remaining quart of oil in the oil pan becomes critical, especially with solid lifters and no oil restrictors in the lifter bores. The stock oil pans are limited to 4-1/2 to 5 quarts of oil because it is difficult for the factory to design a high volume oil pan for a street driven passenger car. That is one reason the factory did not equip high performance cars with HV oil pumps. The GM Corporate Office insisted that all high performance cars had to be driven on the street. The exception was the 409 Chevrolet and the 421 Super Duty Pontiacs which were equipped with a modified stock pan that was welded and extended deeper for 8 quart capacity. Notice how high the front end is on those cars? That is partially for oil pan clearance. This is not a problem unique to Pontiac engines. As far back as 1965, Chevrolet used "edge oriface" lifters with their famous 30-30 fuel injection cams. Those lifters had the oil feed hole on the body of the lifter rather than in the oil groove. I used those lifters in my '56 and '59 Chevys in 1966 through 1969. I have even heard that before 1965, drag racers put pipe cleaners in the pushrods to restrict oil flow to the rocker area. That was before roller rocker arms were introduced an many engines that were so equipped burned up the rocker balls.

I have proven that a HV pump can suck a pany nearly dry with my '69 Firebird 400 street/race car. I was using a Melling high pressure 455 SD oil pump and about 6000 RPM, the solid flat tappet lifters were rattling downb the return road. That was because the stock 4-1/2 quart oil pan was nearly empty at 6000 RPM and the acceleration was pushing the remaing quart of oil in the pan up the back of the oil pan and away from the pick up. When the engine idled for a minute, the oil pan began to refill and the lifter noise went away. I spun out rod bearings on two occasions before I decided to install an aftermarket 7 quart oil pan. I finally switched to a hydraulic flat tappet cam and used Melling JB-951R limited travel (RA-IV) hydraulic lifters. I had no more problems oiling after that. The Crane hydraulic lifter cam and Melling JB-951R limited travel hydraulic lifters were good to 6300 RPM, just like the previous solid lifter cam. I also quit driving the Firebird 400 like it was a 327 Chevy.

Unfortuantely, driving the Firebird like it was a Chevy was the only way I could beat a Chevy.

Last edited by MouseFink; 03-19-2011 at 11:56 AM. Reason: typo
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  #40 (permalink)  
Old 03-19-2011, 11:36 AM
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Quote:
Originally Posted by MouseFink
As I mentioned before, stock volume oil pan should never be used for racing even though some claim to be able to get away with it.

Who told you this . A stock 5-6 quart pan is fine. Tack your pickup that way it is full suction. The pump is a personal matter.
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  #41 (permalink)  
Old 03-19-2011, 02:16 PM
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Did some work today, as i said before there was a new oil pump and pick up as well on the shelf so i've decide to make the mods to get a better hydrostatic balance and keep the stock one wich is in the engine right now.
The grinder i've used is great but the bits not that much so the grooves aren't perfect for sure , i just hope they work.
I've grinded also the casting flashes ,wich on the pick up inlet were very bad, i believe the flow should be better now.
The roll pin has been replaced by a threaded plug and the bypass hole enlarged and the tiny plug replaced with a bigger one (1/4" NPT), unfortunately the wall was thin so i had to braze it up .


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  #42 (permalink)  
Old 03-19-2011, 03:41 PM
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FWIW, the plug will change the static spring tension resulting in a higher pressure to open the regulator. Make sure the cover and body are still flat. I use some 300 grit paper on a mill table or a piece of glass to make sure the covers are flat. The end clearance on the pump gears should be no more than .002".
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  #43 (permalink)  
Old 03-19-2011, 04:15 PM
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The HV pump will fit into a stock oil pan. From what I can see the HV oil pump pick up will be deeper into the oil pan.
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  #44 (permalink)  
Old 03-19-2011, 04:32 PM
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Quote:
Originally Posted by lmsport
FWIW, the plug will change the static spring tension resulting in a higher pressure to open the regulator. Make sure the cover and body are still flat. I use some 300 grit paper on a mill table or a piece of glass to make sure the covers are flat. The end clearance on the pump gears should be no more than .002".
Yes, i'll check for flatness and correct clearance after brazing the pick up.
About the relief spring, do you know how much pressure will increase before the piston will be open? i know it sound pretty silly but i'm obsessed about the load on distributor and cam gear, i guess nothing noticeable, can you confirm this?
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  #45 (permalink)  
Old 03-19-2011, 04:40 PM
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Quote:
Originally Posted by cobalt327
Use a good oil filter, too. The Fram filters have been reported to have problems associated w/pressure loss.

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I had a sudden drop of oil pressure, to zero. I was running a Fram. Never again! Being that some Wix (or Napa brand, same thing) filters are made in China, I've moved onto Baldwin or Hastings filters. Even purolator is a good step up in quality from fram (compare the two at your local auto part store). I made the choice to spend 5 bucks on an oil filter, it's cheap insurance for a $3500 engine.
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