C-3 SB oil pressure

[John D.]

What is the proper range of oil pressure for a 1968 327/350 HP at startup and at operating temp?

I am wondering if I should have a standard pressure or high pressure/high volume pump in the engine.

Thanks

[Joe L.]

Re: C-3 SB oil pressure

John------

The big factor here is the accuracy of the oil pressure gauge. Many stock-type oil pressure gauges are not the best as far as accuracy is concerned. If in doubt, use a test gauge with a larger oil pressure line to verify the accuracy of your in-dash gauge.

Anyway, I would expect a start-up, cold oil pressure of about 40-45 pounds. A hot cruising RPM oil pressure of about 30-35 pounds.

Your engine was originally built with a standard pressure, standard volume oil pump. That's all that I recommend that you use. You don't need and shouldn't use a high pressure or high volume oil pump.

[Brian Monticello]

Re: C-3 SB oil pressure

On my brand new rebuild with a melling m55 standard SB pump, .003 main clearances and .0025 journal clearances I get the following:

- 45 on cold startup - I'm sure the clearances would allow for a higher pressure but I believe the bypass spring kicks in about 45
- 35 at cruise
- 20 at hot idle at about 700 RPM

My in dash gauge is about 5 psi too low. My 327 has a small oil fitting above the timing chain cover and I periodically connect a gauge here to check things out. All a high volume/pressure pump will do for you is give you extra wear on your distributor gear, wear on rear cam bearing, and rob you of some power. Some people with smaller oil pans and low oil levels even run their pans dry becuase the high volume pump shoots all the oil up into the heads.

Brian

[John D.]

Re: C-3 SB oil pressure

Thanks for the info Joe. The current pump is a melling 55HV. I am going to replace it with a standard pump.

Thanks again, John

[John D.]

Re: C-3 SB oil pressure

Joe:

Do you know the GM part # for the standard pump and the number for the oil pick up?

Thanks again, John

[Joe L.]

Re: C-3 SB oil pressure

John-----

Yes, the pump is GM #12555284 and the pick-up screen is GM #3830080. This pump GM lists for $122.37. A Melling M-55 will be, basically, the same and, these days, it might be exactly the same thing. Personally, I always like to use GM for parts like these, but, nowadays, parts like this are often outsourced.

If you do get the GM piece, I'd be interested in knowing if "GM" is seen in raised lettering anywhere on the pump body and/or cover.