Oil Pump And Windage Trays

[Joe R.]

Re: Oil Pump And Windage Trays

Todd,

This thread has a lot of good info on oil pumps:

https://www.forums.ncrs.org/showthre...=2667&uid=6668

Joe

[Timothy B.]

Re: Oil Pump And Windage Trays

Just want to add for anyone that's considering the standard volume standard pressure Melling M-55 pump for a small block rebuild, the relief spring pressure is 55-60psi.

I found this out after installing one in my 67 300hp engine and I wanted 45 psi. After calling and talking to George at Melling they sent me a 49psi relief spring to replace but it sure does not do much good after the pan is back on the engine..

[Mike R.]

Re: Oil Pump And Windage Trays

As Duke points out, GM could have used any size oil pump and pressure they wanted. It would have added no additional cost. If a larger or higher pressure pump was better than they would have put one in and lowered their warranty costs. The fact that they didn't should tell us something.

As pointed out by others in another thread, the Melling M55 does not have the original, stronger, SBC casting. The original pump casting is availible as part 10553 which Melling calls a "High Performance" pump. I actually had a M55 ready to go in my engine until someone posted a photo of the difference and I exchanged it for the 10553. It is only slighty more expensive than the M55. Both are standard volume pumps.

A lot of aftermarket parts are sold with claims (can you say "hotter spark") that seem reasonable but only if you don't understand the problem. In all things there is an optimium.

What Chuck said...

Also, OE replacement pumps, which are all "standard volume" are available with both 40-45 psi relief springs, and 55-60 psi relief springs for the later mechanical lifter 327s that used them.

"High volume" pumps are strictly aftermaket. They were never used for any OE SB engine, and AFAIK all these aftermarket high volume pumps have relief springs in the 60 psi range or higher range.

If you don't understand how the oil pump works - as Chuck explained - do some archive searching as it has all been explained in great detail.

It's important to understand the concept of a "constant volume" pump which is what the oil pump is and how the pressure relief spring works to limit mechanical stress on the pump while still providing sufficient oil volume to the engine.

Up to the point the pressure relieve valve opens, full output volume is delivered to the main oil gallery. Once the valve opens, flow to the main gallery is controlled by the input pressure, which essentially means that oil delivery volume is constant with increasing RPM, and excess oil from the pump, which increases approximately linearly with pump speed is bypassed by the relief valve back into the pump inlet.

A high volume pump will achieve full pressure before a standard volume pump does, but beyond this point, the HV pump is just using extra HP to churn and heat up the oil. Some HV pumps deliver full pressure at idle speed, which is totally unnecessary.

An OE pump with a 40-45 psi relief spring should idle at about 20-30 psi with fully warmed up oil depending on idle speed and oil viscosity and achieve the 40-45 psi by about 2000 RPM.

The high pressure OE pumps will idle at about the same pressure - actually on the high end on high-idle speed mechanical lifter engine and achieve the 55-60 psi by about 2500.

Duke

[Todd L.]

Re: Oil Pump And Windage Trays

Great responses, thank you for all the input. I will go with a standard flow pump. I have a 74' L-4 BB, is there a recommended pump I should use?

[Duke W.]

Re: Oil Pump And Windage Trays

Go to www.napaonline.com and buy a Sealed Power OE replacement pump for your model year and engine.

Duke