L72 427/425 Oil Pump

[Peter M.]

Was the 1966 L72 427/425 original oil pump considered either high volume or high pressure? When replacing the pump, should one specify high volume or high pressure?

[Joe L.]

Re: L72 427/425 Oil Pump

Peter-----

The SHP big block oil pump was a "standard" volume, high pressure. Only ZL-1 big block engines were ever originally fitted with a high volume oil pump.

[Mike Cobine]

Re: L72 427/425 Oil Pump

Due to days of Hot Rod and Car Craft, almost everyone jumps into a high volume pump. However, it is not necessary in most cases. In the solid lifter race motors, we actually used oil restrictors to keep some of the oil out of the lifters.

High volume is often used as a "fix" for engines with excessive bearing clearances.

Now there are places for them, but most do not need them.

In the 302, we ran 80 psi with a high volume pump because we had .0045" bearing clearances. However, we had those clearances because we spun it at 9500 rpm.

You spin a big block all day at anything over 7200 and it won't last but about two hours. (Ask my how I know.)

[Duke W.]

Re: L72 427/425 Oil Pump

Automotive oil pumps belong to the constant volume class. If you dump the output into a bucket the delivery volume will increase approximately linearly with pump speed until it cavitates.

In an engine the constant delivery characteristics will cause pressure to buildup due to the bearing and other clearance restrictions. Thus, they are equipped with a pressure relief valve that shunts the output back into the input once the relief valve pressure is achieved. At this point, oil delivery to the engine is a function of pressure difference, not pump volume.

A "high volume pump" will achieve relief valve pressure at a lower speed than a pump with less delivery volume, and unless you street engine has excessively loose clearances, only a standard volume pump is necessary. A racing engine with very loose clearances may need a high volume pump to maintain target oil pressure.

For street engines or light racing the normal OE pump delivery volume and pressure is perfectly adequate. A "high volume pump" will just consume power pumping extra oil, most of which is shunted back to the inlet.

Duke

[David N.]

Re: L72 427/425 Oil Pump

Mike,

OK, I'll ask the proverbial retorical quest that everyone has in mind, "just how do you know?" That said, as a fellow BB owner, I expect that it cost you at least one blown engine.

David Nims member #19639 save the wave~~~~~~~~~~~~~~~~~~

[G B.]

BB vs. SB difference

I personally believe there is a huge difference between the valve train oiling efficiency of the big block vs. the small block.

I've never encountered a small block that needed a high volume or high pressure oil pump for long life on the street. In fact, I've had two customers with HV pumps that emptied the oil pan at freeway speeds!

My big block experience shows just the opposite problem. Standard volume BB oil pumps send very little oil to the rockers at low rpm, even with tight bearing clearances. I've used the HV/HP LS7 GM oil pumps for years in 427/454 street applications with great success. They do not pump the pan dry on the freeway, and at idle there is enough oil to the lifters/rockers to minimize wear.

[Clem Z.]

Re: BB vs. SB difference

you must use piddle valve lifters in BBC engines because of the heavier valve spring pressure they use. the SBC edge orifice lifters do not allow enought oil to lube the rocker arm balls and cause wear. grooved rockers balls will also help as the were not used on all BBC from the factory.

[Joe L.]

Re: BB vs. SB difference

Jerry-----

I agree exactly with your assessments.

[Mike Cobine]

Re: L72 427/425 Oil Pump

Yes, it did. 427, August, 1992, Daytona, NASCAR Turn 1, second SARRC race, at roughly 170 when it ceased to generate power or even rotate without effort.

BTW, it is surprising at how much you can hear from the infield while coasting at 170 mph.