Oil pressure and oil pump

[Donald H.]

I have my engine out due to frame off restoration and getting ready to replace the oil pump. My car is a small block L79 66. I've owned the car about 3 years and the engine had a fairly recent rebuild when I purchased it. However the re-builder install a M55HV and my pressure was running very high. Someone also put in an 80 lb gauge, so that's something else I will correct.

I have purchased a Melling 10553 pump and install the green 49# spring.

I was talking to a friend who is a very good engine builder and he says the pump should have the 60# spring and thus relief pressure of 60#. He says he has GM documentation to back this up and that the 49# spring is wrong.

From my research on this forum, what I think is correct is that some (or all starting sometime in the 63 model year), solid lifter small block cars with 80# pressure gauges used a pump with the 60# relief. However, the hydraulic lifter small blocks used a 45# relief pump and have a 60# pressure gauge.

Is this correct? And is there GM documentation that confirms this?

Thanks,

[Duke W.]

Re: Oil pressure and oil pump

Basically correct, and you can verify in the AMA specs for your year and engine option. The actual hot oil pressure spec is 30-45 @ 1500, so even the green spring will likely be too high.

Don't forget to correct your buddy so he doesn't screw up a bunch of engine rebuilds in the future. Show him the AMA specs and ask him to show you the documentation he claims states 60 psi.

Mechanical lifter 327s small got a 55-60 psi relief spring in the standard volume pump and an 80 psi dash gage from very late '63 production through '65.

Duke

[Donald H.]

Re: Oil pressure and oil pump

Thanks Duke.

I'll get the AMA specs and have them handy.

Don