Performance Verification C2 Oil Pressure

[Mike M.]

The performance verification test guide book says that the oil pressure should be mid range after warm up. My gauge was checked and should be accurate. I have a melling M55 series pump in the engine. The readings are high compared to what the guide says. 60lbs or more when you step on it. In order to pass the performance verication you need 100% and this will not pass. Anyone have a sugestions on a oil pump that will give me correct readings. Should I go with a stock GM pump? Is it still avaiable? Or should I leave the pump and recalibrate the gauge so it looks like the readings are correct. I'm not sure if this is even possible.
Mike

[Mike M.]

Re: Performance Verification C2 Oil Pressure

buy a stock pump(GM or aftermarket) don't get the LT1 type pump which is a high vol/high press pump. these lt1 style pumps installed on midyear smallblocks account for a good many PV failures. at idle, when warmed up, the judge will dislike a pegged oil press guage. good luck with your PV. they are tough but once ya pass one3 it'll be the most exhilirating thing you've done with your wranglers on and zipped. mike

[Mike M.]

Re: Performance Verification C2 Oil Pressure

Thanks Mike,I thought that might be the best way to go. Does anyone have a part number for a stock GM oil pump for a 65 327/350hp L79. Mike

[Loren L.]

Why not just seek out 5 quarts

of 5W-20?

[Mike M.]

Re: Why not just seek out 5 quarts

believe the idle oil press with lt1 pump will still peg guage even if the lower viscousity oil is used. mike

[Duke W.]

Re: Performance Verification C2 Oil Pressure

As far as I know all the SB oil pumps of the era were essentially the same. The only difference between the "45 psi pump" and the "60 psi pump" used on mechanical lifter SBs beginning in late '63 was the relief spring, and there might be some variation in pickup design depending on the pan design, which depended on the chassis for various models.

Any OE replacement oil pump from a quality manufacturer should be up to the job.

Duke

[Patrick H.]

Re: Performance Verification C2 Oil Pressure

Mike,

Realize that the M55 "is" the same pump you'd get from GM, just a different box. Assuming you do not have the "high pressure" or "high volume" versions I'm not sure how much you would gain in changing pump.

Might I also suggest it might be from a newly rebuilt engine? In my 71 I also kept higher pressures than expected (40-60lbs) until I had a few thousand miles on it. Also, as an FYI, I run pressures that are 10lbs less when I run Mobil1 than when I run Duke's Diesel Oil.

It would be a lot cheaper and easier to swap oils or put more miles on the motor than to swap oil pumps, which I would think would give you minimal benefit if any, "assuming" you don't have a HP or HV version.

Else think the gauge. It only take a few minutes to take an inexpensive aftermarket gauge, hook it up to the port on the back of the block, and see what your pressures are with a different gauge. If they are the same there may be little benefit in changing gauges.

Patrick

[Mike M.]

Re: Performance Verification C2 Oil Pressure

I found the bill for the pump and its a Melling M55A. I was told this pump was the right one when I bought it.I am running the diesel oil that Duke recomends. I'll try changing oil and see if that helps. I have about 1000 miles on the engine now. I tried another gauge and the idle readings are the same. I didn't trying driving with it hooked up though. I agree with you about changing the oil pump, its a lot of work. I don't think it will pass the PV test with the pressure that it has now. Thanks Mike

[Mike M.]

Wrong Pump M55A

Answering my own question here. I just talked to Melling about the pump. That is the high pressure version. To bring the pressure down I need the M55. I should have talked to them before hand instead of the parts guy. Thanks Guys for the information, but it looks like I'll be changing a pump this spring.Mike

[Michael F.]

Re: Performance Verification C2 Oil Pressure

ok guys flame me; i think ncrs is way to ANAL if they worry about oil pressure reading, prove to me what they were in "the day" bet you can't, anyway, hobby should be to preserve not to be anal, my 2 cents, by the way I have been into corvettes since 1971 and first joined, then quit ncrs in the 70s so i do support but not to the degree of oil pressure judging. thanks, to each his own is my motto.

[Mike McKown]

Re: Wrong Pump M55A

Mike:

Call them back and see if the only difference is the spring. They may send you one and it would save you some money.

[Joe L.]

Re: Wrong Pump M55A

Mike-----

I believe that the Melling pumps use the same relief spring as GM pumps. If so, what you need is spring GM #3814903 which is still available for a few bucks GM list. This will convert the pump from high pressure to standard pressure.

Usually, when I buy a GM pump for a small block, I purchase the high pressure pump and then change the spring to this one. I have this silly notion that maybe the high pressure pumps are made of better material or to more stringent tolerances. I know, it's likely very foolish, but it only ends up costing me a few bucks for the "peace of mind". It's very easy to change the springs. Literally, a 1 minute job.

If you do want to purchase the GM pump (which MAY now be actually manufactured by Melling) here are the numbers:

standard pressure---GM #12555284

high pressure-------GM #12555884

[Mike M.]

Thanks Joe & Mike

I'll look into changing the spring. I never even thought about that. Mike

[Patrick H.]

Re: Wrong Pump M55A

When I spoke with a VP at Melling back in 1996, they were supplying the small block oil pumps for GM and I suspect they likely still are.

Patrick

[Joe L.]

Re: Wrong Pump M55A

Patrick-----

GM used to internally manufacture the oil pumps for small block V-8s. I believe that these were manufactured at the GM Bay City, Michigan engine parts components plant. However, as the Gen I and II small block engines began to be phased out by the late 90s, it would be completely understandable that GM would switch to another supplier for the parts. Generally, GM in-house manufacturing operations (at least, those few that remain under GM corporate ownership) only produce high volume type components; others are usually "outsourced".

At the present time, the Gen I and II small blocks are produced for SERVICE only; NONE are used in PRODUCTION vehicles, at all. It would be VERY unusual for GM to manufacture, in-house, a component like oil pumps when these oil pumps are either used only for SERVICE engines or sold for SERVICE replacement for earlier engines. So, I would fully expect that the oil pumps currently available from GM and those available in the future will be manufactured by a source like Melling. That's not to say that the Melling (or otherwise) manufactured oil pumps available through GM are the same thing as those which are supplied in Melling boxes under their brand name. They may be the same or they may not be the same.