396 Oil Pump

[John O.]

Hello Everyone,

I need to ask for some opinions regarding a good replacement brand oil pump for the 396/425 engine. I don't want a high-flow pump as the car is going to be flight judged and I want the gauge to read correct for the ops check. As always thank you all for your great input!

John Osterholm

[Clem Z.]

Re: 396 Oil Pump

GM still sell a BBC oil pump with the correct pickup for mark IV corvette oil pans BUT it is a high volume pump. i do not know if it has a pressure increase. part# 3969870

[Joe L.]

Re: 396 Oil Pump

clem and John-----

The GM #3969870 pump is BOTH a high volume and high pressure pump. In PRODUCTION, it was used only for ZL-1 applications (NOT L-88 applications, as some folks selling this pump on eBay advertise). The 1965 Corvette with L-78 used a high pressure oil pump which produced the same pressure as the 3969870. So, as far as oil pressure gauge reading, the 3969870 will produce a correct reading. The "high volume" part of the 3969870's design will not "show" on the oil pressure gauge. It may, however, cause other problems. Quite frankly, I doubt it. Big blocks are generally very much ok with high volume pumps and many PRODUCTION big blocks did use high volume oil pumps. The situation is NOT the same for small blocks, though. GM never produced any PRODUCTION or SERVICE small block engines with high volume oil pumps (although GM does sell a high volume pump in SERVICE for those that want to fo this route).

Other than the high volume issue, the GM #3969870 pump will fit and work perfectly for a 1965 L-78 application.

GM no longer offers an oil pump which is an exact replacement for your application. I don't think that Melling does, either. However, you can obtain a Melling M-77 pump and change the pressure spring to the high pressure type. This would give you as close to an exact original configuration as you can get. The high pressure spring is not available from GM anymore, but I think they are easily available in the aftermarket.

[James W.]

Re: 396 Oil Pump

John,

I would be more concerned about the operation of the pump during the PV testing not the flight judging ops check. If it is wrong during the PV test you fail, period! My question to Joe and anyone doing or that has done a PV test is what should the normal oil pump presure be as seen on the gauge at cold start-up and what should it be at hot idle? If the pump that Joe is recommending meets the PV test perameters, that's the one I'd put in. Also is the pump installed on the engine now the incorrect one? I'd get a part number off of it and verify what you have first. The pump you have now may be exactly what you need.

James West

[Mark #28455]

The M77 is essentially a knockoff

The GM std volume pumps came in essentially two flavors - std pressure and high pressure - the main difference was the spring in the pressure relief system. That's exactly what melling is selling - one pump with two springs, just pick your spring. The std pressure spring comes "pre-installed" as that's the one 95% of the buyers will use. Why bother marketing and stocking a whole second pump when you can just toss in the spring for about 10 cents. I have used this pump with the swapped spring on several of my engines, the cold pressure for my engines was about 60 to 70 psi and the hot idle pressure was about 35 psi which would rise to about 60 psi at maybe 2000 RPM. Remember, hot pressure is dependent upon the viscosity of the oil, the bearing clearances, the idle speed, whether you installed the lifter galley plugs with the holes to lube the timing chain, etc. Cold pressure is also variable, and then just how often has your guage been calibrated. So, it's a ballpark figure! All in all, the Melling pump works about the same as stock.

On the other hand, you can take a stock pressure pump and shim the spring with one or two approx 1/4" thin flat washers - don't laugh, it really works! But I'd rather use the non-Bubba'd Melling part.

Mark