oil pressure

oil pressure

Joined: February 8th, 2011, 1:23 am

July 7th, 2012, 4:44 am #1

I was messing with the timing in the stock car motor today and I noticed that above 4k the oil pressure slowly falls off about 10psi by 5k. All of the clevelands I have built have done this. What causes this?
oil pressure is 70psi cold idle
hot idle is 30 psi and gets to 60 psi by by 3500, and then starts falling off above 4k down to 50psi by 5k.

9qts of 10w30
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Joined: December 16th, 2003, 11:56 pm

July 7th, 2012, 6:00 pm #2

where you see this happening.
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Joined: February 8th, 2011, 1:23 am

July 7th, 2012, 10:26 pm #3

no lifter bore bushings
restricted cam bearing oil
restricted pushrods
.002 on the mains with full groove bearings
.0025 on the rods and .020 rod side clearance
hv pump with std spring. regulates at 70psi
8qt pan with pickup .25 off the bottom of the pan
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Joined: December 16th, 2003, 1:59 am

July 8th, 2012, 12:07 am #4

$2 on the pick-up being too close to the bottom of the pan

there'll be phantoms, there'll be fires on the road... and the white man dancing
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Joined: May 20th, 2005, 4:48 pm

July 8th, 2012, 12:12 am #5

no lifter bore bushings
restricted cam bearing oil
restricted pushrods
.002 on the mains with full groove bearings
.0025 on the rods and .020 rod side clearance
hv pump with std spring. regulates at 70psi
8qt pan with pickup .25 off the bottom of the pan
The second number means the most when the engine is hot...I like to run a 15W-50 or close to that for my hipo stuff.

I've seen the same deal that you've seen on the dyno, but I've found that when you add viscosity or cool the oil down, it will hold its own. This especially helps with the hydraulic rollers as it will help keep the lifters pressurized.

I do a lot of hydraulic and solid roller stuff and I've never used lifter bore bushings. I run HV pumps, restrict oil to the cam (either by screw-in restrictors, or the restricted bearings that Tim sells), and set the bearing clearances at about .001"/inch of journal diameter. My mains are usually between .0027-.003 and the rods are usually around .0025". Now granted, most of my engines have hp peaks that fall between 6000-7000. For the guys turning to 8000 rpm and higher, you may have to get a little fancier...

Brent Lykins
B2 Motorsports, LLC






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Joined: December 16th, 2003, 1:59 am

July 8th, 2012, 5:16 pm #6

$2 on the pick-up being too close to the bottom of the pan

there'll be phantoms, there'll be fires on the road... and the white man dancing
* unless you've been using the same oil gusher roller lifters in each build that you're speaking of?

and even if that is the case, 1/4" is justa little too close IMO. once the pump starts getting some good suction going the oil can become a 'coupler' that will draw the bottom of the pan closer yet to the pick-up

what you're seeing at 5k is an 'out of oil' scenario for whatever reason



there'll be phantoms, there'll be fires on the road... and the white man dancing
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Joined: December 16th, 2003, 11:56 pm

July 8th, 2012, 5:49 pm #7

no lifter bore bushings
restricted cam bearing oil
restricted pushrods
.002 on the mains with full groove bearings
.0025 on the rods and .020 rod side clearance
hv pump with std spring. regulates at 70psi
8qt pan with pickup .25 off the bottom of the pan
.25 clearance seems too close but depends on pickup geometry and relationship to bottom of pan (level). Restrictors in pushrods probably not a precise means for oil control. How much oil is collecting in valve covers? Need more specific details of what exactly is in the engine for all restrictors, lifters, push rods/restrictors and size of restrictor in push rods. lifter/bore clearances? Too many things if data not collected when built, probably start with at least a heavier weght oil -40 or -50, go from there. Where/how do you use the car. Seems as though pump is starving for input flow, pumping dry or restricted at input. not likely, but frothing of oil may also cause issues. is this a street car?
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Joined: October 1st, 2004, 8:05 pm

July 8th, 2012, 10:18 pm #8

I was messing with the timing in the stock car motor today and I noticed that above 4k the oil pressure slowly falls off about 10psi by 5k. All of the clevelands I have built have done this. What causes this?
oil pressure is 70psi cold idle
hot idle is 30 psi and gets to 60 psi by by 3500, and then starts falling off above 4k down to 50psi by 5k.

9qts of 10w30
With the 351C ... the drop off of oil pressure as rpm climbs indicates lubrication problems ... it's a classic Cleveland problem. But oil pressure that holds steady as rpm climbs does not necessarily indicate the lubrication system is OK. It is possible to have plenty of oil pressure and still starve the rod bearings for oil. The first question - what's the condition of the bearings when you tear the motor down? That's the bottom line. If the bearings are in great shape, then the problem is not a major problem. If the bearings show signs of inadequate lubrication, then this is a big problem.

In your case the oil pressure is dropping off at lower rpm than normal. Here's some ideas ... I'm just brain storming you understand:

>>Agree with Tin the oil pump pick-up may be too close to the bottom of the pan

>>The oil pump suction line may be too small in ID

>>The oil filter may be too restrictive (Fram?)

>>The lifters you've chosen may be interacting with the Cleveland lifter oil passage in such a way to create this problem

>>Too much clearance between the lifters & lifter bores

>>Aeration of the oil, pan needs windage tray & scraper

>>Oil level in the pan is dropping too low

>>Centrifugal force is causing the oil in the pan to slosh away from the oil pump pick-up during high G force situations (acceleration, braking or cornering)

>>Heat ... the oil is getting too hot and the viscosity/pressure is dropping off

__________________________

By the way, I am in agreement with your choice to use the pushrods to restrict oil to the valve train ... assuming your motor is using a hydraulic camshaft & lifters. That's really the only way to do it with hydraulic lifters. It doesn't help at all with solid lifters however.

-G
____________________________________________________________

Pantera Photos | 351C Historic Information | 351C Technical Information

Last edited by gpence on July 8th, 2012, 10:29 pm, edited 1 time in total.
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Joined: January 10th, 2002, 5:53 pm

July 9th, 2012, 12:09 am #9

I was messing with the timing in the stock car motor today and I noticed that above 4k the oil pressure slowly falls off about 10psi by 5k. All of the clevelands I have built have done this. What causes this?
oil pressure is 70psi cold idle
hot idle is 30 psi and gets to 60 psi by by 3500, and then starts falling off above 4k down to 50psi by 5k.

9qts of 10w30
I wish I could add something - but I've never seen the problem. Which seems kinda unusual after reading. I make sure the pickup is at least 1/4, better 1/2 off the floor. I ran plenty of 10w-30, usual pressure - picked up at the back of the block - would be 35 hot and 60 at 2400 staging RPM, same 60 psi in the lights at 6000. I switched later to straight 30wt, same pressures. Cold would be 70~75 psi.

1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.
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Joined: August 23rd, 2003, 12:49 pm

July 9th, 2012, 10:25 am #10

I set the pickup at 10mm from the bottom of the pan. IMHO 1/4" is too tight.

I have never used full groove bearings(and never will) or a HV oil pump in a cleveland either. If you set the clearances up correctly the engine should maintain 60/70 psi @ full noise.
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