Some Thoughts on Oil Pressure, Oil Pumps and Oil Viscosity

Bob In Ct · #1 (**permalink**) 11-08-2002, 05:54 PM

A few thoughts on oil pump, oil pressure, oil viscosity and oil filters.

Oil pumps are not rated for pressure, they are rated for flow. If you have a certain model pump it will flow a certain amount of oil at a given RPM. The flow will be X gallons of oil per minute at that RPM regardless of the oil viscosity. Since the flow is predetermined by the pump manufacturer, the pressure is determined by the tightness of the engine and the viscosity of the oil at any given RPM. The tighter the engine the greater the pressure. The thicker the oil the greater the pressure.

Most oil pumps are equipped with a pressure relief valve. This is a device that will only allow the pressure to get so high. Once that pressure is achieved, the valve opens and a percentage of the pumped oil is allowed to return to the crankcase. The remaining oil is pumped through the engine. This is why many of us reach a certain oil pressure, and no higher, regardless of the RPM or oil viscosity. That being said consider the following two identical cars –

Car “A” is using 5W-30 oil. At 5,000 RPM the oil pump is pushing X gallons of oil per hour. The oil pressure gauge shows 60 PSI. Car “B” is using 20W-50 oil. At 5,000 RPM the oil pump is pushing the same X gallons of oil per hour. The oil pressure gauge shows the same 60 PSI. In both cases the pressure relief valve is limiting the pressure. Because the 20W-50 oil does not flow as easily, more of it is being allow to return to the crankcase without flowing past the bearings and past the cam and past the rockerarms. Although both engines show 60 PSI the engine with the lower viscosity oil is flowing more oil through the engine (assuming the pressure relief valve is open).

More food for thought. Joe’s oil pressure sensor is between his oil pump and his oil filter. Bill’s oil pressure sensor is after the oil filter. Both Joe and Bill decide to try the new WIX oil filter. After installing them Joe has lower pressure while Bill has higher pressure. How can this be? The answer is simple. Joe’s old filter was restrictive and produced high pressure at his sensor since it was located downstream of the sensor. Bill’s filter, is located in front of the sensor and is now producing higher readings since the oil is better able to flow through it. If Joe were to switch to heavier oil he would show higher pressure. If Bill were to switch to heavier oil he would see a reduction in pressure.

Conclusions -

Do not attempt to compare your oil pressure to your buddy’s since he (or she) probably has a different oil pump, a different filter, and higher/lower viscosity oil.

Assuming the same pressure and RPM, thinner oil will flow more volume through the engine than will thicker oil.

Higher pressure is not always better. Too much pressure is tough on more than just oil filters.

Bob

Mr.Fixit · #2 (**permalink**) 11-08-2002, 07:29 PM

Keep your oil pressure gauge pickup AFTER your filter, cooler, and any other crap you cram it through before it gets to the main galleys. Then as long as it stays above 15 at idle and 35 at speed, you should be fine. High volume pumps add heat to your motor oil because they circulate so much more oil through the pump and bypass, yet no more through the motor. And run a WIX racing filter.

Hal Copple · #3 (**permalink**) 11-08-2002, 08:02 PM

i have run several different Wix racing oil filters, they make some really beefy ones, which i have on my Ernie Elliot NASCAR filter adaptor, but the inner outlet is a huge 1.5 inches. But they do make others, too.

check out: http://www.wixfilters.com/racingnews...=410&Section=7

hal

niles · #4 (**permalink**) 11-08-2002, 08:23 PM

Do anyone have any specifics and specifications on the "racing filters". I always wonder just what we are getting. I could speculate that they maybe high flow/high pressure/rugged filters that are'nt to concerned with particulate size. Does anyone know the mircon specs?

gn

RICK LAKE · #5 (**permalink**) 11-08-2002, 08:39 PM

Oil pressures and oil viscositys T he boys of Nascar are using W0-30 oil for racing. The motor only lasts 600-700 miles. The golden rule is 10 lbs for every 1000 rpms. I do not think this work at 10000 rpms. An Alky funny car when start up and idle( if you can call it that is 175 lbs. By the end of the track it is about 50 lbs and the oil is destroyed due to fuel in the oil. Nascar looks like about 60 to 70 lbs at speed depending at what track they are racing. Does anybody use a sandwich filter like Oberg or Omni. Gyann GT 350 is the only one, it is reuseable, clean with brakekleen and reassembly. Different filter screens are available. When I put the dry sump on I am thinking of going to one of these filters. You would need to tap the last bearing to get oil to know the correct oil pressure of the engine. Years ago someone sold an oiling system for the 427 side oiler to get more oil to the mains. It taped right off the oil filter housing. the side bolts where hollow for the oil to flow through them. I have a 100 psi spring in my motor and a high volume pump. When the motor is hot I get 40 psi at idle 750 rpm and goes to 75psi at 2200 rpm. I think its safe, but not for pulling 1G inautocross and roadracing. The better cars all use dry sump systems just like Nascar. Rick Lake

Bob Parmenter · #6 (**permalink**) 11-08-2002, 10:52 PM

Attaboy Bob!!

Finally, I no longer am the only one around here that emphasizes flow first, pressure second. We might quibble about minor differences in your commentary, but, quite frankly, it wouldn't be worth it as your general concept is spot on.

scottj · #7 (**permalink**) 11-09-2002, 05:54 AM

Rick,
I run the Oberg\Omni on the return side before the tank -16 in & out and check it every time. I use a paper filter, Wix\Napa Gold, after the pump, it's less restrictive than the screen. Catch screens on the suction side protect the pump. Are you going to vent the engine or run vacuum?
Scott

scottj · #8 (**permalink**) 11-09-2002, 06:06 AM

niles,
20-28 micron on the paper racing filters and 60(fine) or 115(coarse) micron on the screens.
Scott

RICK LAKE · #9 (**permalink**) 11-09-2002, 06:26 AM

ScottJ I will try to vent the engine first. If this doesn't work than I will add the pump and go that way. The problem is I am running out of room under the hood, between coolant tank, P/S pump, supercharger, and Alt. The only thing I am missing is the A/C compressor and the kitchen sink.

More wieght on the front end also. Not the best place. O Well Got to go Rick Lake

scottj · #10 (**permalink**) 11-09-2002, 06:43 AM

Rick,
Not a seperate vacuum pump, but using the drysump pump and sealing the engine to run vacuum. You gotta love silicone though

Speaking of making room under the hood, have you seen those Racemate altenators that are built into the water pump pulley? not sure if he does them for FE's??

niles · #11 (**permalink**) 11-09-2002, 03:53 PM

ScottJ:

So the racing filters are passing 20-28 mic. I'm I correct in thinking that most street type filters are more like 10 mic? If this is correct why would a racing type filter be better for a cobra application?

thanks

gn

scottj · #12 (**permalink**) 11-09-2002, 04:39 PM

niles,
I'm not sure about standard filters but from what I've read and seen in my own engines, the racing filters won't pass anything that could cause bearing damage. If my math is right, 20-28 microns equals .0007-.0011 inches and bearing clearances are usually .002-.003. The truth is I don't know if it's beneficial for a low RPM street engine, but from my experience I don't think it could hurt the engine.
Scott

RICK LAKE · #13 (**permalink**) 11-09-2002, 04:42 PM

ScottJ Hey Scott those alt under the water pumps have been out for 2 years. The problem is the amount of amperage out put In the beginning there was only 38-40 amps. Now think they are up to 60 or 70 amps. One problem, when at idle their is no charging, the pulley spins to slow. Nascar used them until too much amparage was need in the cars. Some may still use them I am not sure. Silicone,RTV,Pipe Dope, High Tack, and bubblegum are all I use to seal my motor.

I think you can get a 3 micron filter for the Oberg filter. I would run a 10-12 one. What oil pressure are you running when racing??? I know that the pump has a regulator. What are your pulley teeth gears #. I do not want to turn more than 6200 rpms till I get my steel crank in 2 years and chevy rods. I want to go to 480 cubes with 15 lbs of boost. that will be all the car I want. In 3 years I want that Car and Driver ultimate race to go play in and maybe One lap of America. I may need bigger brakes, 13 inch and a 3 channel ABS system installed. We will have to see?

Got to go shopping Rick

scottj · #14 (**permalink**) 11-09-2002, 05:24 PM

Rick, 60-70 amps? I wish mine had that, I have 30 something and your right, the lights are a little dim at idle.

Bubblegum?

Your killing me! I've never seen the 3 micron but you may be right, my catalogs only show the 60 & 115.
I use the 10 lbs per 100 hp guideline or 75-80 lbs on the aluminum engine and 65 lbs on the Cobra. Both engines underdrive the oil pump 50%; pulleys are 32/16 on the Cobra and 40/22 on the Aluminum. I turn the Cobra 7000 and the aluminum engine 8200 when there's traction and 7500 or less when the track slicks off.

480 ci and 15 lbs! what do you think that will make? 8-900ft/lbs?

You want to go shopping? PRI show is the week after Thanksgiving in Indy. I'll be there... dreaming only.

Scott

RICK LAKE · #15 (**permalink**) 11-09-2002, 09:32 PM

ScottJ Scott in the mid 90's Oberg claimto fame was they could catch particles down to 3 microns. I wonder what the restriction from the filter was in gallons of flow?? How big a tank are you running for your dry sump? Why not put a mini alt on the car with 60 or 80 amps? You know their are other places to put a mini alt. No not in the wheels. Mr driveshaft spins and is doing nothing that would hurt or affect the alt. All you need is two wires or one if you like and away you go. 38 in the front and 60 pushing out the back. People will laugh but I have seen it work. I have a very small cam 501-533 I may go to a 530- 566 next step up. Hprw should be about 670 tork about 740 no slicks the Jag rear will not hold up. I have done everything to it, 30 spline stub shafts,chromemoly short shafts, watts linkage for the rear, rear cap girdle for the carrier. Locker Detroit. I want a big flat fat tork and hp line to 6500rpm. The G-Force will handle the power. Scott are you going to come to Run&Gun in Oct 2003? Hope soon want to see your car run. Beddy by time, the other half is in a teddyyyy gottogooooooooo later Rick@#$#$$%%%^^&**&!@#

scottj · #16 (**permalink**) 11-10-2002, 07:54 AM

Rick,
I found info on the 3 microns, I just don't have anything under 60 listed in any racing equip catalog. I wonder about restriction too, I know the 60 in the top of my tank won't pass oil unless the pump foces it to. When I check the screen the bottom cavity is empty and all the oil is in the top cavity above the screen. I've waited a week to open it and the oil still hasn't passed through the screen, makes a nice mess all over the top of the tank.
I've got 3-1/2 gal tanks, a round Peterson in the Cobra and the other is a Butlerbuilt with a built in 60 micron Racor that is custom for the GRT chassis.
I've thought about a driveshaft driven alt but not for charging reasons, I wan't to run 1:1 pulleys on the waterpump and I can't with the Racemate.
Oct R&G is on for '03 since it no longer conflicts with my other schedule. I'm pushing my buddy with the Ultima to go too although I know that thing will smoke my Cobra.
Scott

Dave Wharran · #17 (**permalink**) 11-10-2002, 04:20 PM

I've ran an Oberg model 600 for years on the VW. Went to what they called a fine mesh screen early on. The 600 used about a 6" diameter stainless screen.
Wanted an Oberg for the GT40. Found out that the Racor division of Parker had bought Oberg. I finally ended up finding getting one from the local truck parts store. About $135 of $145 if I remember correctly. Don't remember the PN offhand, but it is the old Oberg model 600 with Racor's name on it. The fine screen is about 28 micron according to the factory. I always get the bypass warning light kit along with the filter. Had a cam go flat on the VW in first 5 minutes of running on a new engine. The bypass light went on. I ignored it for 5 minutes till cast iron plugged up the oil holes and the engine started to seize. Duh. Costly lesson not to ignore the bypass light...ever.
You can examine the screen at each oil change for bits of whatever. Makes it easy to see if something is wearing and releasing metal particles in the oil.

PERUCH · #18 (**permalink**) 11-10-2002, 11:57 PM

Anyone used SYSTEM ONE oil filter ?

scottj · #19 (**permalink**) 11-11-2002, 06:08 AM

Behling Racing Equipment 800-255-4117 has the original Oberg 600 Series w/60micron screen pn 518-6001 for $108.11. The light kit is $34.59 and the 28 micron screen is $55.79. He also carries the System 1.