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How much oil pressure is too much?
#1
Hey gents, yet another question. I have a VDO 80 psi electrical oil pressure gauge in my car, and the recommended sending unit, obviously when engine is cold and I fire it up, it reads the full 80 psi value, once its warm, while I am driving it stays pegged, but at idle it does come down to 35-40 psi, I had all the Tim Meyer oil mods done to this engine, and lifter bushings. Will these mods cause a higher than normal pressure? The problem is the needle now wants to "float" above 80 psi in almost all rpm ranges above idle. The oil pump is a stock pressure/volume pump, and I don't blow filters anymore, just have high oil pressure. Is this bad?
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#2
Have you consulted the modifier of the oil system of your engine? Seems like they might know whether that pressure is excessive or expected.
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#3
Where is your sending unit mounted? If it is at the back of the block it will read lower than at the plug above the filter. After that pressure bleeds down as oil passes the lifter bores and pressure bleeds off. I'm not a fan of excessive pressure, but it is flow that creates the bigger problems when the oil all ends up in the valve covers.

Electric gauges used to be less accurate than mechanical. I'm not so sure that is true anymore. I'd watch for leaks at the valve covers and seals and if you don't see any I think you'll be fine.

Your mods, specifically the lifter bushings and tight bearing clearances will cause higher pressure than normal at the gauge as they don't allow pump pressure to bleed off as much before reaching the sending unit. Keep in mind your crank is still downstream in the oiling system and sees a bit less pressure.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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#4
I would say this is probably one topic that has no definitive answer. While working in a racing shop in the 60's & 70's we built engines for mainly circle track racers. We did have a few customers that ran drags but they were not as popular in our area. They shut the 1/4 strip down in 60's said it was too loud.
I would see bearings to start to show wash out after 1,000 - 2,000 miles of racing on the track. Think of the pressure like your pressure washer the higher you go with the pressure the more damage you can do to something. The whole oiling concept inside an engine is not to blow up the gap around the crank with oil and the crank and bearing never touch. You want the correct bearing clearance to allow the oil in without having so much space that they hammer together and cause failure and enough pressure to feed the oil in.
Since you put bushings in the lifter holes that should help with any excess oil loss there and get the oil to the crank.
Look at some of the small engines we run every day they have no oil pressure at all and they scream. When me and son raced carts we ran the 5 hp. Briggs engine. Like most of the small engines it is splash oil only with a dipper. There is no bearing insert only the die cast aluminum rod. The wrist pin in your engine has no pressure oiling and has the same forces to contend with as the crank just no velocity of the surface, much more friction there. So with the more flow of oil it also helps to cool the crank and bearings.
The little box stock engines with splash oil would turn about 5,000 rpm if the gear was correct, seen 7,000 when not, and you did not lift your foot for the 15 lap race if you had correct set up. The modified engines went to double that still splash oil. We never had a rod or crank failure in years of racing. We didn't even use the aftermarket rods your were allowed to use. We did tear the engine down and check everything each week and replaced the valve springs. I guess my point is that it takes very little oil to prevent a bearing and crank from failing due to friction. Failure usually comes from too much heat or something foreign in the oil to cause a bearing to fail.
When you change your oil filter cut it open with one of the fancy can openers that splits the folded seal. Look for any signs of metal there and if you do see metal consult with your engine builder show him what you found. In NASCAR today they are not allowed to change engines like they did years ago, qualify one race another. They check the filter before race and change the engine if they find anything. That oil filter is like doing a blood test on yourself. It tells the health of your engine and if something if failing.
A built racing engine will never last as long as a stock build with higher compression and higher valve spring pressures parts do not last as long.
Just my thoughts,


When a man is in the woods and talks and no women are there is he still wrong??
Tongue
David
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#5
I would remove the sending unit and connect a good mechanical 120 psi gauge to the same port to both compare to the electrical gauge readings and to see what you're getting when it's cold.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#6
Omie01;266861 Wrote:Hey gents, yet another question. I have a VDO 80 psi electrical oil pressure gauge in my car, and the recommended sending unit, obviously when engine is cold and I fire it up, it reads the full 80 psi value, once its warm, while I am driving it stays pegged, but at idle it does come down to 35-40 psi, I had all the Tim Meyer oil mods done to this engine, and lifter bushings. Will these mods cause a higher than normal pressure? The problem is the needle now wants to "float" above 80 psi in almost all rpm ranges above idle. The oil pump is a stock pressure/volume pump, and I don't blow filters anymore, just have high oil pressure. Is this bad?

Exactly what oil are you using now?

How high is your gauge capable of reading?
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#7
My 393 from Tim runs 60-70 psi hot at idle with VDO a mechincal gauge, using Valoline VR1 10w30.
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#8
FWIW my 1973 351C with new AutoMeter gauge and sender runs about 80psi cold and idle, 35 or so hot idle, 70-75 driving with engine hot and cruise rpm 2500 or so. I thought it was high too but no oil leaks showing. Runs great. I didnt rebuild motor so I cant speak to clearances etc in it.
Also, as too accuracy. If you want you can contact sender maker and get the "ohms chart" for that sender. The sender is electronic and basically a variable resistor. Every PSI change against it causes a mechanical slider to move inside. that changes the resistance to ground (ohms) and meter moves. So they have a chart at factory for testing them that says , for example, with 20 PSI, it should read 197 ohms (+/-) small tolerance. So if you look on chart, find your 70 PSI or whatever your idle is, you can pull OFF the sender wire and measure ohms to ground of engine from that tiny stud. Thats the internal resistance of that sender at one set psi. See if it matches the chart and you know you have a good valid reading (vs getting a mechanical sender),
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#9
The 73 AMA spec says oil pressure should be 50 - 70psi at 2000 rpm for the 351C. My car runs about 65 -70 psi at 2000rpm and 45-50 psi at idle when hot. I did not do any oiling mods to my car.

-john
(jbojo)
351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,
C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

Some Mod pictures can be seen at:

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#10
OK everybody, false alarm. I was going to install a 100 psi gauge last night, but when I was disconnecting the wires to sending unit I found it was really loose, so I tightened it back up and wham!! It works perfectly! 35-40 at idle, not more than 75-80 top end. Lesson learned: check wires first!!
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