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Melling M-72 Oil Pump Performance Upgrades for Poly A-block and LA Engines
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Posted 2023-04-22 2:57 PM (#629061)
Subject: Melling M-72 Oil Pump Performance Upgrades for Poly A-block and LA Engines


Posts: 137
Location: Denver, Colorado, USA

I documented the process I use to convert a Melling M-72 oil pump to high pressure, blueprint, and port the pump in this video. The Melling M-72 is used on 1962 - 1967 A-block 313 and 318 and all LA 273, 318, 340, and 360 engines (1956 - 1961 A-blocks use a Melling M-51). The M-72 can be tuned up easily for optimal flow and higher pressure for performance engine builds.

A well-cemented misconception largely pushed by pump manufacturers and corporate automotive magazines and TV shows selling advertisement space is that a high-volume pump is a must-have for all performance engines--in this case the Melling M-72HV. However, the vast majority of A-block and LA-block performance engines will see no measurable benefit with more oil volume over what the standard-volume M-72 with the porting I show in the video can flow. The A/LA oiling system is well designed and provides ample volume to most components. As an aside, I'm working on another video that details modifications to the oiling system to address the pitfalls of the factory system such as the crankshaft thrust bearing and the timing set. What a lot of people don't realize is that the design of a high-volume pump eats up more engine power than a standard-volume pump, and a lot of people bolt on a high-volume pump without considering the factory spin-on oil filter adapter plate. The factory adapter plate has but four 1/4" diameter holes that limit volume passing from the pump into the filter to what the standard-volume pump can flow. I've taken apart many A and LA engines to find a high-volume pump and a stock filter adapter plate; little did the previous engine owners know that their fancy high-volume pump wasn't actually providing above-factory volume to the engine components at the cost of using up more engine power since the filter adapter plate restricted the pump's volume. The correct modification is to either drill additional holes in the factory adapter plate or purchase a high-flow aftermarket plate with larger holes.

A far better option for the majority of performance A/LA builds and not a bad idea for even stock builds is to increase the oil pressure to 65 - 70 psi at running temperature above 1,500 rpm while using a lower-viscosity oil like 10W30 (or even 5W20 for builds with tight bearing tolerances and when the engine won't see cold-start temperature under 40°F). The lower viscosity oils use less power to pump, and the higher pressure provides ideal protection to the moving parts. Unfortunately, Melling doesn't produce a high-pressure pump, but Mopar Performance has a high-pressure spring kit. In the video, I cover which spring to buy and how to remove and replace the factory spring with the high-pressure spring.

Food for thought for you performance A and LA enthusiasts out there.

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