C1 327 oil pump

[Terry K.]

I have a silly question on the oil pump, it’s associated sump pick up tube, and the pressure spring. Years ago I had a very reputable engine re-builder go through my 327 – 300 HP 62 Corvette motor. When we first fired it up, the oil pressure would drop to zero on hard acceleration, but it come right back up after letting up on the gas. These guys figured out pretty quick that the small block oil pump sump pick up tube was not getting down far enough into the 6-quart oil pan. My recollection is that they told me they put in a big block oil pump that had a longer pick up tube. These guys were “engine guys” – not “Corvette guys”! That solved the first problem, but created a new one. The oil pressure was now pegging the gage.
“Someone” told me that the only difference in the BB vs. SB oil pump (besides the sump pick up tube) was the size of the pressure relief spring; and that all I had to do was change the spring. Is this true? Also, what – if anything – will be damaged if the very high oil pressure is not corrected?

[Duke W.]

Re: C1 327 oil pump

The 327 oils pumps were all the same, except a 55-60 psi relief spring was added to mechanical lifter engines in late '63. The standard relief spring is 40-45 psi, which is more than adequate for the 300 HP engine and also basically okay for L-79 and mechanical lifter engines for normal street use.

I not sure, but I think the pickup tube is the same length for the pan setups as they are the same depth.

There is no reason or need to "improve" the OE pump other than maybe adding the 55-60 psi spring to earlier mechanical lifter engines that didn't have it, but the the 60 psi gage is going to be pegged all the time. Mechanical lifter engines with the higher pressure relief spring have 80 psi gages.

In my own case my '63 L-76 never suffered any oiling problems even though it has the 40-45 psi spring and plenty of race track hot laps over the years.

Duke

[Joe L.]

Re: C1 327 oil pump

Terry----

"Someone" told you wrong. There are numerous differences between a big block and small block oil pump, although a big block pump can be adapted to work with a small block. A big block pump has a much higher VOLUME than a small block pump due to longer gears and more "teeth" on the gears. Plus, many big block pumps operate at a higher pressure than the standard pressure small block pump. The main "advantage" to using a big block pump on a small block is that the additonal "teeth" on the gears provide for smoother operation and less distributor oscillation (i.e. the oil pump is driven by the distributor). For a street engine this "benefit" is negligible. On the down side, the big block oil pump requires more hp to operate, so there's a loss here.

Another problem is that I don't know of ANY GM oil pump pick-up that's designed for use with the big block oil pump and the C1 style oil pans. I don't know of any aftermarket ones, either, although there may be some.

The only difference between the SMALL BLOCK standard pressure pump and high pressure pump is the relief spring. So, if "someone" was talking about this difference rather than the difference between a big block and small block pump, then they were correct.

I'd say you have these options:

1) keep the current big block pump (if that's actually what you have), but change the pressure relief spring to a GM #3860378. This is the lowest pressure spring that GM offers for the big block oil pump. However, it may still be too high for your needs and it's even possible it's the one in there now; I don't recommend this option;

2) replace your oil pump with a GM #12555284 or a Melling M-55 (NOT a Melling M-55HP or a Melling H-55HV). If the Melling M-55 pump is supplied with an additional pressure relief spring in the box, don't use it. Just keep the spring that's in the pump. IF you have a stock type 1962 Corvette oil pan (i.e. "3 step" with oil drain on bottom of lower sump) , then use oil pump pick-up GM #3764113. This set-up should work perfectly and return you to completely stock configuration;

3) If you actually have a small block pump installed, but with a high pressure spring, then you can change the pressure spring to a GM #3814903 spring and that should solve your problems. However, make sure that someone has not installed a HIGH VOLUME small block oil pump, too. You don't need or want that. How do you tell the difference? The geras are longer in a high volume pump. If I recall correctly, the standard pump gears are 1.3" long and the high volume pump gears are 1.5" long. I'm not 100% sure of these numbers, though. If you have a high volume pump, change it to one of the pumps I described above.

2)

[Randy S.]

Re: C1 327 oil pump

Joe

Terry's last question was what if anything would be damaged by the high pressure. I'd like to know too. I have similar issue with my 66 300HP but at 1000 mi/year do I need to change it?

Randy

[Joe L.]

Re: C1 327 oil pump

Randy------

No damage will be caused by the high pressure pump. Some have reported a little more oil leakage at various locations from an engine equipped with a high pressure pump. I've never verified that or experienced it (mainly, because I've never used a high pressure pump).

Also, you don't need to change the oil pump if all you have is a high pressure pump. All you need to change is the pressure relief spring. If you ever have the pan off for any other reason, you can easily do this at that time. It only takes a few minutes extra.

[Randy S.]

Re: C1 327 oil pump

Thanks Joe.