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Re: Too much oil pressure?
the problem with excess oil pressure is extra wear on the distributor gear and camshaft gear that drives the oil pump. the max oil pressure you need at max RPM is 10# per 1000RPM. 60# at 6000RPMs is plenty. also i would try a different gage befor you change anything.
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Re: Too much oil pressure?
It sure sound like you have a high pressure oil pump or your oil pressure guage is not accurate. The pressure will vary on the type of oil used such as 5 30 or 20 50.
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Re: Too much oil pressure?
Tom-----
As Motorman and Chuck have indicated, your first step should be to check the accuracy of your gauge. Your 73 uses a gauge which directly senses oil pressure through a metal tube. To test your gauge, I would temporarily intsall a "T" fitting at the block oil pressure line fitting. Install your dash gauge tube to one of the "T" outlets and install a test pressure gauge connected to the other. For the test gauge, use as large of diameter flexible tubing to connect between the "T" and the gauge as is practical. Then, check your dash gauge against coincident readings obtained from the test gauge.
If your pressure is confirmed to be high, it may be as a result of a high pressure oil pump having been installed or a standard oil pump which was modified to increase relief pressure. In this respect, the first thing that I'd do is to remove the oil pan and oil pump. Then, remove the oil pump relief spring and replace it with a GM #3860378. This spring only costs $1.25 at your GM dealer and, using it, you'll know that you have the correct spring for your engine.
If, after this, you still have excessively high oil pressure, we'll need to look at other, more serious potential causes. In addition to the problems identified by other responders, excessively high oil pressure can cause other problems like higher oil consumption and, especially, make the engine much more prone to oil leakage. I DO NOT RECOMMEND high pressure or high volume oil pumps for most Chevrolet engine applications.In Appreciation of John HinckleyComment
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After 17,000 miles....
and no problems, why worry now? What kills a motor when a high pressure pump is used is the oil gets blown through the bearings without lubricating anything. If any problems would have occurred, they would have occurred with the first 500 miles of operation. If you want to know what is your oil pressure, get a good mechanical gague from Summit.Comment
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Re: After 17,000 miles....
high oil pressure will not hurt anything other than what i said in my other post. i have see dry sump chevy race engines run at 100#+ oil pressure with no bad results. high oil pressure robs HP and fuel mileage, that is why late model engines have less oil pressure than before. VW diesel engines ran 125# oil pressure cold and if you ran a non VW oil filter you could blow it off.
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I beg to differ with you...
Excessive oil pressure WILL starve the bearings of lubrication. Now, there are exceptions to the rule. Drag motors with excessive clearances MUST use high pressure pumps.
Diesels are completely different animals, and play no part in this equation. Normal street engines with factory clearances, max oil pressure should be no more than 80 lbs. The dry sump motors, if you check, have been clearanced and would sound like a tin can full of marbles, if run on the street.Comment
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Here's the deal, guys
Actual hydrodynamic oil pressure in a bearing will reach several thousand pounds per square inch, and it's this hydrodynamic action in the bearing (like "aquaplaning" on a wet road with thin treaded tires) that keeps the journal 20 to 40 microns from the bearing. The oil pressure we see on the gage is merely the feed pressure which supplies the bearing with oil during that part of the 360 degree rotation cycle when there is no hydrodynamic pressure at the point of the oil feed hole. Like flow through a carburetor, the greater the pressure differential, the higher the flow rate. On street engines which generally have restricted oil capacity, higher than necessary oil pressure can fill the engine with oil faster than it can drain down which can possibly starve the engine. Also, all that oil gets whipped around by the rotating/reciprocating assembly and can heat up the oil and cause excess windage drag. The general recommendation for a racing SB or BB is 10 psi of oil pressure for every thousand revs or 90 psi for a 9000 RPM Winston Cup engine. So for a street engine that occasionally briefly sees 5000 to 5000, 40-60 psi is sufficient, and I think hydraulic lifter engines were typically speced at 40-45 psi and some of the mechancial lifter engines were as high as 60.
I notice the original post mentioned that the gage "pegs" but there was no mention of the highest calibration on the gage. I assume it's 60 psi. For a street driven engine the higher than necessary oil pressure is probably not harmful, but I would go with Joe's advice and verify pressure with a test gage, and if it is too high, remove the pan and pump and install a new, correct relief spring.
I received some very interesting information from Bruce Crower about all the IRL engines that have blown up in the last three years. I was interviewing Bruce specifically about the flat-eight and flat-twelve Indy engines he built in the late seventies using Cosworth Vega cylinder heads, but we got into quite discussion about the IRL engine reliability issue. The biggest problem turned out to be the location of the crankshaft oil feed holes. At 10,000 revs there was insufficient time to supply oil to the journal. It took a lot of experimentation and many blown engines, but they finally came up with feed hole locations that can supply sufficient oil, and the engine reliability should be much better this year.
DukeComment
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Re: Here's the deal, guys
the placement of the oil holes in the crank are very important to engine life. one trick used on high rpm chevy engines is to groove the main bearing saddles under the mains and drill 4 extra holes in the main bearing insert, 2 on either side of the main hole to allow the oil to enter the crank easier as it is turning at high RPM. the main journal oil holes in the crank are then ground to lengthen them for a better oil flow. this practice is even used on some stock GM engines. the placement of the rod journal oil holes on some aftermarket crank cause problems because they are drilled for convenience not for durability.some cranks even use 2 different location for the rod feed holes on the same journal.
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Re: Here's the deal, guys
That's basically what was done to get the IRL Auroras to live, particularly the locations of the rod journal feed holes and "fillets". I've got a buddy who wrecked two 305, 18 degree head, Hilborn injected small blocks in two and a half runs on the 1.3-mile El Mirage dry lake course with his fiberglass repro P-38 belly tank Lakester because of an aftermarket crank. After building a third engine with a Crower crank he had it dynoed for about thirty minutes, and it pulled a corrected 620 horsepower at 8200 on gasoline.
DukeComment
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Re: Here's the deal, guys
Duke:
Hey, nice response to the question!
I have a question for you related to this thread. I saw here, and on Corvette Forum, reference made to 10# pressure for each 1000 rpm's.
I take it that this is not a linear relationship - that is 10 psi at 1000 rpm's and 60 psi at 6000 rpm's - but only at the top end.
My 350/300 shows 35 psi at idle and 45 psi on the road at about 2500 rpm's. I can't recall ever seeing it outside this range. Without knowing anything else about modifications to my engine, would you suspect the guage?
The engine was rebuilt by the former owner with TRW pistons, Sealpower rings, and an Edelbrock Performer cam. Would these mods affect the oil pressure?
Thanks.......JimComment
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Re: Here's the deal, guys
Jim - The ten by 1000 rule applies to a racing engine and is the recommended pressure at high sustained revs based on the maximum revs. Ten pounds per thousand revs is adequate at all revs, but oil pump designs typically deliver more oil at idle and low revs, so pressure is usually above the 10 by 1000 rule, but won't deliver enough volume of oil at idle and low revs to make rated pressure. As engine speed goes up delivery volume is increased, which increases pressure. Once the rated pressure is reached, the bypass valve opens and excess oil is returned to the sump. Depending on the grade of oil and oil temperature, rated pressure is usually reached in the 1500 to 3000 PRM range. Your 35 psi at idle RPM and 45 maximum sounds right on the money for a 327/300, but if you drove the car in traffic in very hot weather the idle pressure would probably drop a bit. Your oil pump delivers more than adequate volume for your engine and you could easily increase the pressure by installing an appropriate bypass spring, but it's not necessary for the type of service your engine sees.
As a side note, some manufacturers in the seventies equipped engines with low volume oil pumps which only provided about 5 psi at idle and 20 to 25 psi max. The reason was to reduce internal parasitic loss in the search for better fuel economy. High oil pressure/flow rates take horsepower and so do high coolant flow rates. You can bet that the Winston Cup guys run the minimum oil pressure/flow and coolant flow to make the engines live, particularly on the restictor plate engines. A handful of horsepower can make the difference between a podium finish and mid-pack.
DukeComment
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I don't know Duke of Earl, if that is entirely....
correct. Winston Cup guys running low oil pressure. These guys are twisting 8K R's. That's a lot of heat, and if the oil is not there, well they pay big time. Think you may have to rethink what the Winston Cup guys are using for pumps. H.P. is critical, but not at the expense of a blown motor. Can't win a race with a spun bearing.
Tell ya what, I'll place a wager that says they are running at least a high volume pump, and say 50-60 lbs pressure. A brewskie on the wager?Comment
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Re: I don't know Duke of Earl, if that is entirely
cup cars all run dry sump pumps which pump lots of volume which in more important than lots of pressure. we won a 300 lap race one time with just 20# of oil pressure at wide open throttle in a BB chevy. something cause the pressure relief valve to stick open but it never hurt the engine. oil flow is what is realy important.
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No bet, George
The point I wanted to make is that Winston Cup engines probably run less than the rule of thumb ten psi times RPM or 90 psi for a 9000 RPM engine. I don't know what they actually run because it's about as hard to get current info on Winston Cup engines as it is to get current info on F1 engines. The lower the oil pressure the less the internal friction loss in the engine. Same with the coolant pump flow because both are parasitic losses. I'd also bet that they are running no more than 60 psi, maybe even lower. If I were building racing engines I would figure out what the lowest oil pressure and coolant flow would be for the engine to live and then optimize the designs of the pumps to be most efficient at the flow rates and speeds they would be operating at during the race. For a restricted long track engine the rev range is generally between about 6800-7200, and if the engine would live at 20 or 30 psi, that's what I'd run, because it would free up a few extra ponies at the flywheel.
Flow rates are a function of both pressure and the restriction that the fluid is flowing through. A typical automotive oil pump flow increases with pump speed. If we mount an oil pump on a test fixture and just dumped the output into a bucket, there would be very little pressure developed, and we could determine the flow rate as a function of pump speed. But on the engine the oil is being pumped through relatively narrow passages and the bearing clearances form a restriction to the flow, so pressure builds up, and the "looser" the engine, the more oil will flow at a given pressure. That's why an old engine with worn bearings will sometimes not reach rated pressure. There just isn't enough volume to build rated pressure if there is insufficient restiction. Like the carburetor flow rate issue of a week or two ago, quoting oil pump flow rates without a pressure drop or vice versa is meaningless, but oil pumps are rarely specified this way. What we get sold is a "high volume" oil pump, which basically means it will make more pressure (if we choose to install a high pressure relief spring), particularly on a "loose" engine, but it will also cost some horsepower.
DukeComment
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