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Topic Review (Newest First)
12-16-2008 07:12 PM
ScoTFrenzel Maximum pressure is determined by the tightness of the oil pressure bypass spring.
If it is a 60 psi spring setting, then all the oil volume that creates pressure will bypass when the valve opens therefore limiting the pressure to that chosen 60 psi.

If your situation is showing an actual amount of 85 (or whatever) that is obviously LESS than the amount needed to open the pressure bypass valve.

Needless to say, hotter thinner oil will not create as much pressure per rpm.

IMO you definitely have a high pressure pump.
I prefer backing the spring down to 60-65 psi maximum.
12-15-2008 05:21 PM
oldbogie
Quote:
Originally Posted by y2k600f4
I have a 383 stroker (less 1K on build) with a 7qt oil pan (total system capacity with oil filter almost 8 qts); running 10W40. I just installed a sunpro electric oil pressure gauge and at cold idle (600-1K RPM) I am seeing ~75PSI and ~85PSI at RPM. When the engine is warmed up to operating temp (160 F) I am seeing a drop in oil pressure at both idle and higher RPMS of ~10PSI to ~65PSI (Idle) and ~75PSI at higher RPMs (numbers approximate). I was wondering if anybody had a thought if the engine builder possibly put a high volume/high pressure oil pump in ? Thanks.
This looks to be a high volume pump, the idle pressure with these will be high with a narrow increase, if any, to high RPM pressure. The change from cold to hot pressure is normal when oil looses some viscosity as it heats up; multi-grades less so than single weights but they all do it to some extent.

Basically the difference between a high volume pump and a standard pump is the size of the gears, high volume having a longer set of gears in a deeper cavity, or more teeth in a wider cavity. These move more oil which will show itself as a higher pressure at lower RPMs than a standard capacity pump. This assumes back to back testing on the same engine with the same bearing clearances as pressure in an engine is the difference between the volume the pump puts in against what leaks out the bearing clearance and/or is popped off by the relief valve.

Pressure, or more exactly maximum pressure, is established by the spring force controlling the relief valve. This is independent of pump size, it's just that a larger volume pump gets to the relief pressure at a lower RPM than does a standard capacity pump.

Often people shim the spring or replace it with a stiffer one on standard volume pumps to increase their maximum pressure. These will show more pressure than a standard pump once the RPMs reach a point where the relief valve opens. Below that point the pressure will look like a regular production pump.

A high volume pump may also be configured to provide more maximum pressure, again, with a shimmed or a stiffer replacement relief valve spring. These will show more pressure everywhere when compared to a high volume pump with a standard pressure relief spring.

There are a number of us hanging out in these parts that feel the SBC does not have enough at and off idle oil pressure for hard working engines, we, therefore, are proponents of high volume pumps to boost lower RPM pressure. There's just as many folks hanging around these parts that feel the standard pump is just fine. Where you live probably has a lot to do with this; here in the mountainous and deserty west it always struck me that the warranty replacement of failed SBC bottom ends justified more pump and heavier oils than these energy savings types in engines that have to put out hard work from point A to B. Especially in these hotter running, higher geared EFI engines, I think it's easy to get these to lugging when hot and the oil film in this low pressure 0W-nothing swill gives up on a long mountain grade at 120 degrees of outside air temp and 220-250 degrees of coolant temp.

Bogie
12-15-2008 05:03 PM
327NUT Before you do anything....why don't you call the engine builder and ask him which pump he installed???? While you're at it ask him about running 5w30, also as mentioned before, if your clearances are tight then the 10w40 might be a little thick. You could try some 10w30 and see what you get for pressure but it won't make too dramatic of a change.

I've got a stock Melling's M-55 in my 331" sbc and cold I peg the 80 psi gauge. You'll find that most guy's on this forum use the stock M-55 pump, the high volume, high pressure just isn't needed on a street car and in fact can be detrimental in some cases as you eluded to in your original thread.
12-15-2008 02:15 PM
y2k600f4 Thanks 68NovaSS and Jsup.

My guess was the high oil pressure was due to tight tolerances and was just concerned if I should worry about anything. I was having some issues of possibly oil blow-by past the rings and while investigating I was curious if high oil pressure could attribute to the problem, maybe too much oil in the cylinders and some is getting past the rings ? I was running 10W30 and changed to 10W40 due to my other problem.
12-15-2008 02:09 PM
Jsup
Quote:
Originally Posted by y2k600f4
I have a 383 stroker (less 1K on build) with a 7qt oil pan (total system capacity with oil filter almost 8 qts); running 10W40. I just installed a sunpro electric oil pressure gauge and at cold idle (600-1K RPM) I am seeing ~75PSI and ~85PSI at RPM. When the engine is warmed up to operating temp (160 F) I am seeing a drop in oil pressure at both idle and higher RPMS of ~10PSI to ~65PSI (Idle) and ~75PSI at higher RPMs (numbers approximate). I was wondering if anybody had a thought if the engine builder possibly put a high volume/high pressure oil pump in ? Thanks.
It's a new motor, it's tight, give it some time.

Go to 5-30. I couldn't get my needle to stay in the gauge, topping 80 PSI even at idle, with 10-40. With 5-30 it sits about 60 PSI and up close to 80 under load.
12-15-2008 01:56 PM
68NovaSS The amount of oil pressure you see is dependant on much more than the pump installed, i.e. bearing clearances play a major role. Impossible to guess what pump you have.
12-15-2008 07:54 AM
y2k600f4
Do I have a high volume or high pressure oil pump ?

I have a 383 stroker (less 1K on build) with a 7qt oil pan (total system capacity with oil filter almost 8 qts); running 10W40. I just installed a sunpro electric oil pressure gauge and at cold idle (600-1K RPM) I am seeing ~75PSI and ~85PSI at RPM. When the engine is warmed up to operating temp (160 F) I am seeing a drop in oil pressure at both idle and higher RPMS of ~10PSI to ~65PSI (Idle) and ~75PSI at higher RPMs (numbers approximate). I was wondering if anybody had a thought if the engine builder possibly put a high volume/high pressure oil pump in ? Thanks.

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