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Lets talk about oil pump relief valve springs


FBBO Gold Member
FBBO Gold Member
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7:25 AM
Jul 15, 2009
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This is on my 451. Motor was put together years ago and had a Melling M-63HP pump on it. I never wrote down the actual oil pressure #'s, but know it wasn't out of the ordinary. I run Valvoline VR1 10w-30. Fast forward to 2 years ago. I had the motor freshened up by a different shop. They reused the old pump, which was fine/normal. When I got it back in the car, I noticed that the hot idle pressure went way lower that it used to. I'm guessing the new build has slightly more bearing clearance than previously. Cold start pressure is 76psi, warmed up going down the road 60mph at 2800rpm = 64 psi. Those 2 numbers are fine imo, but at hot idle 850rpm it is only 17psi. I realize that a lot of people would call that good, but I wanted to experiment a bit to get a bit higher idle pressure, maybe to 25psi or so.
Yesterday I installed a Melling M-63 HV pump. It has been raining and will be for a couple days, so I haven't got it out on the road yet. In the shop, cold start is now 78psi and at 180 degrees rev'ed up to 2800rpm it is 73psi. Hot idle does look to be in the mid 20's. So I believe I accomplished my goal at hot idle, but would like to drop the other 2 numbers a bit.
I took the pump apart and cleaned it before installing and did notice it had a black spring.
So my question is, will a softer/shorter spring drop the high #'s into the 60's but leave the hot idle unchanged?
I cannot seem to find anyone selling the supposedly stock pressure "red" spring to experiment with. That leaves me to attempt cutting some off the black spring in there now. How much would a guy cut off to make a little difference?
Crazy talk….buy and old stock pump and rob the spring out of it. Your ideas sounds correct
In the Melling HP catalog, they list pump springs. I know for a fact that they have GM, but should have Mopar as these are just different pressure springs for Melling pumps.
What kind of valvetrain parts? Is the cam grooved for full time oiling?
Get a stock red spring from any junk oil pump laying in the floor or in the trash at a buddy's house. That will bypass at around 55 psi but still give you good idle psi. The black spring bypass is generally around 75 psi.
I would keep/use the black spring. Some oils are friction modified. That is oil company code for thinned out oil to get good gas mileage. In this country, I can buy non - FM oil that gives about 10-15 psi more oil pressure at idle.
Here's a rebuild kit with both springs and everything else to rebuild a standard volume pump, kinda pricey though.
I'm a fan of high volume/standard pressure pumps. If you've ever primed an engine, a high pressure pump will ask a lot of your drill. Plus no risk of snapping an intermediate shaft or balloon your oil filter during start up in cold weather.

Melling K-63 Melling Oil Pump Rebuild Kits | Summit Racing

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Little update to this post. Did some digging around in my shop and found 3 old pumps that I had saved from motors I had stripped down years ago and forgot all about. Inside them was a black, red, and purple springs. So I was able to do some experimenting. First thing I learned is that just warming up the engine while sitting in the garage is not a good inclination as to what the oil pressure will be when the oil is up temp after a 10 mile drive, pressures will go down.
First I installed the oem red spring. Cold start 50psi, held at 3K rpm 47psi, warm idle 22psi - I did not drive the car.
Added a 1/4" lock washer behind the spring. Cold start 55psi, 3K rpm cruising 50 psi, hot idle 22 psi @ 870 rpm.
OEM black spring with 3/4 coil cut off. Cold start (not done yet), 3K cruising 60 psi, hot idle 22 psi @ 870 rpm.
Wish I would have driven the car with the black spring that came with the HV pump, and that is my next step, just to see what it does when the oil is hot.
My take on the subject at this point is that with 10w-30 oil and a HV pump I am going to get 22 psi at hot idle, which should be fine, and a lot better than the 17 psi I previously had. The guys who built the motor do mostly race stuff, so I am certain they build motors with more clearances. I do know that they run 20w-50 in everything, so that would make sense. I think with my current spring and 10w-40 or 20w-50, pressures would be about perfect. However, from the reading I have been doing, it sounds like more volume with a thinner oil is more desirable. Also, I run 10w-30 in my other cars and that would make my life simpler.
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What kind of valvetrain parts? Is the cam grooved for full time oiling?
Trick Flow 240 heads, Racer Brown HFT cam, Harland Sharpe needle bearing rockers. No idea if the cam is grooved.
Found the spec sheet for the motor.

That's a lot of main bearing clearance. It won't hurt anything, but it bleeds more oil, so when you get in a hot idle situation, the oil pump only flows "X", and you have less oil pressure than you would have at .002" main clearance.
if they honed the lifter bores that would really lower your idle pressure.
In my experience, lifter bore clearance bleeds more oil than large bearing clarances. You have proven what those in the know have said. Relief spring pressure has nothing to do with idle pressure. You've also learned that water temp and oil temp take two very different time lines to achive. The last thing I will add. After experimenting with various amounts of oil pressure at running temps. The difference between 60psi and 80psi at temp in my racecar made no difference in ET. We moniter oil temps. My sons car and mine require two different vicositys to achive proper running oil temp pressure. Mine runs 25w at 125-150 degree oil temp. His has a filled block and requires 50w as the oil temps can achive over 200 degrees.
if they honed the lifter bores that would really lower your idle pressure.

Even without honing the lifters. People never think about the lifter bores. They think they are fine. They never measure or check them. These blocks are 50 years old folks. If you leave the intake manifold off when you prime the oil system there is an unbelievable about of oil leaking around them. In the old days there was .005" oversize lifters available. That would be a big benefit to our 50 year old blocks.
when I rebuilt my 440 in my 67 Newport the lifters would plump right down in the bores which I rather have loose then tight my oil pressure was low when hot at 700 rpm in drive. went with 15w-40 instead of 10w-30 and it helped the car even run better with the thicker oil better ring seal maybe.
So is this .020" rod side clearance a bad thing? Is it common practice by some builders?
Stock is .009 -.017.. people run way more.
The rod clearance shouldn't be a concern, the .0027 is the restriction
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