L-71 oil pump

[Kieran A.]

Is GM oil pump #3969870 an acceptable replacemnet for the original #3876868? The engine is completely stock. Thanks in advance for your input.Kieran #11373

[Joe L.]

Re: L-71 oil pump

Kieran-----

The GM #3969870 is the 1969 PRODUCTION oil pump for ZL-1 Corvettes. This is a high pressure, high volume oil pump. Although not catalogued by GM as a direct replacement for the last available L-71 oil pump, GM #3904826, I believe that it will work perfectly for the L-71 application and it's still available from GM.

Better still, the GM #3969870 is supplied complete with an oil pick-up tube and screen that will work perfectly with a Corvette oil pan, but not with some other Chevrolet oil pans. In fact, I think that's why that GM did not catalogue the 3969870 as a replacement for the 3904826. The 3904826 (successor to the 3876868) was used for several different big block SHP applications, many of which were not in Corvettes. Since the 3969870, with its attached pickup tube/screen would not fit ALL of the 3904826 applications, GM could not show the 3969870 as being supercessive to the 3904826. So, the 3904826 was, officially, discontinued without supercession.

In point of fact, the 3969870 does produce a somewhat higher volume than the 3904826. This should present no problem, though, for a big block.

[Bill Braun 33186]

Question.

I've heard differing opinions about replacing "normal" volume oil pumps with high volume pumps, generally in the direction of oil displacement to the top end and the resulting insufficient amount of oil available for the bottom end. Is there any basis to this? I could see where a smaller capacity oil pan combined with a high-volume pump might lend credence to the theory.

Bill Braun 33186

[Kieran A.]

Re: Question.

Joe, you mention that the #3969780 is a high pressure/high volume oil pump.Since you believe that the higher volume is not an issue in a big block,would you recommend that a pressure relief spring #3860378 be used with the 80# oil pressure gauge? I have seen several cars that routinely show excess oil pressure on the gauge.Thanks for your response,Kieran #11373

[Craig S.]

Re: Question.

Bill - the bearings and lifters control the amount of flow through the oiling system, the additional flow that is excess is bled back to the pan through the bypass circuit in the pump itself. The higher volume pumps usually deliver higher oil pressure at idle when not, due to the increased capacity. They also consume more HP to run, and if you don't need it, the extra effort just goes into the power to run the longer gears and dumping oil through the bypass circuit. The pump Joe references here however I have used several times in BBC buildups with no probles at all. It is also set up for the Corvette Oil pan as far as pickup depth and curvature of the pickup tube to clear baffling inside the trap door pan, and it pickup is already tack welded to the pump body for safety. In my book, this is the pump to use on vettes for BBC engines.....Craig

[Joe L.]

Re: Question.

Kieran-----

The GM #3969780 is equipped with the same pressure relief spring, GM #3876866, as the original L-71 pump. So, from an oil pressure standpoint nothing will change with its use on an L-71. I would use the pump as-is on an L-71. If you want to reduce the "gauge pegging" condition, you could change the spring to the GM #3860378. I wouldn't, though.

[Joe L.]

Re: Question.

Bill-----

I don't recommend the use of high volume oil pumps on small blocks. For big blocks, high volume oil pumps are fine.

[Kieran A.]

Thanks,Joe *NM*