HV vs Std Oil Pump Info

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nm9stheham

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Another FWIW post... my son and I were drilling out the exit passage in a new Melling HV SBM oil pump today and decided to practice on an old standard oil pump from a '68 273. Afterwards, we did some comparative checks on the 2.

1. Rotor height: Std .829" ; HV 1.034"
That's a 25% height increase for the HV pump, and that agrees with the advertised 20-25% flow increase. That increase due to rotor heights would be the flow change into little or no restriction, so is not necessarily the increase in flow into an engine with no output pressure change.

2. Castings looked pretty identical inside. Lube for the shaft is a little different and more generous for the HV pump. This older std pump has a square o-ring cover seal and the new HV has none.

3. Relief valve pistons looked the same but the HV pump's step that is the rest stop for the valve is a bit further back, and puts more preload on the spring. But the location of the fixed end of the spring does not change, so I don't think that preload has any effect on the relief pressure by itself.

4. Springs looked identical but the spring wire diameter on the HV pump measured .069" and that on the .066". That works out to about a 20% stiffer spring rate. The fixed end point for the spring is at the same place: the plug.

With the stiffer relief valve spring, it looks like this pump will indeed push a somewhat higher pressure and push more oil into the engine than a standard pump, even with no engine changes. And, with the larger rotor height, it ought to continue to do this down to a lower RPM. (But I did not check the location of the relief port to be sure.)

I don't think the load change on the engine will be any higher than the 25% of rotor height.

Again, FWIW.....the floor is now open for comments, refutations, fist-fights, etc. LOL

Pix of older std pump inside followed by HV pump inside:
 

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The std mp pumps have a spring that gives 55-65 psi oil pressure.

You can replace it with the high pressure spring to get 75 psi...

All mellings pumps come with a 72 psi spring whether std volume or high volume....
 
VG info! & oiling mods are important/critical. A person might go to www.moparchat.com then scroll down to & click on "circle track chat" then peruse Sanborns' oiling mods that are in a sticky at the top of the page in addition to Guitar Jones' oiling mods (some overlaps)
 
The std mp pumps have a spring that gives 55-65 psi oil pressure.

You can replace it with the high pressure spring to get 75 psi...

All mellings pumps come with a 72 psi spring whether std volume or high volume....
Just so I am not confused.... this HV pump is a Mopar Performance HV pump PN4286589-001 on the box, but the pump itself looks to be actually a Melling M72HV; that number is stamped in the casting...... In that case, your info 'splains the heavier spring.

So is it just the MP STD pumps that have a lower spring pressure.... assuming it too is not actually a Melling.....? (And presumably the older stock pump too.)
 
Do you think MP really makes anything...just a reboxed Melling pump with a MP part number...
 
Just so I am not confused.... this HV pump is a Mopar Performance HV pump PN4286589-001 on the box, but the pump itself looks to be actually a Melling M72HV; that number is stamped in the casting...... In that case, your info 'splains the heavier spring.

So is it just the MP STD pumps that have a lower spring pressure.... assuming it too is not actually a Melling.....? (And presumably the older stock pump too.)


We dove into that in January in my how to change a pressure relief spring thread.

Mopar uses the std 55-65 lb spring in both their std and HV pumps. You can buy the high pressure MP spring to get them to 75 psi.

Mellings all come with the 72 psi spring. Mellings does not use the 55-65 psi spring.

Neither Mellings or MP could tell me who made the MP pumps. The MP pumps seem to be a different manufacturer than Mellings, but I could not find anyone in either company that could verify that...

http://www.forabodiesonly.com/mopar/showthread.php?t=301617
 
Do you think MP really makes anything...just a reboxed Melling pump with a MP part number...

Chrysler buys their parts from outside suppliers.

It's just which ones that we don't know. They can also change suppliers sometimes.... #-o
 
This particular MP HV pump has the Melling number cast into it and looks exactly like this, including how the numbers are cast in......But they certainly could get them from more than one supplier.

https://www.enginekits.com/m72hv-melling-oil-pump.html

The spring rate difference we got from the measurements matches up right on the difference between MP and Melling that you listed: 72 is 20% higher than 60....which is the spring rate difference we found.
 
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