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Another Oil Pressure Thread

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prb51

prb51

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Ok, on all older cars the oil pressure greatly exceeds what is accepted today.
Almost all old oil gauges read in the 60 to 90 psi realm.
I'm told that a motor needs from 7 to 9 lbs of pressure for every 1k rpm and most modern cars register around 32 +/- psi regardless of the rpm.
Why do our older Tr's require such pressure. What mechanical advance allowed for the difference then/now?
 
tdskip,
Yes, too a point, but the machining and tolerances on our cars is not that dramatically diff.
I've seen folks here argue that the high oil pressure most of us gauge watchers seek just robs the vehicle of some HP and that the 9 lbs per 1k rpm is sufficient and that's why I ask the question.
Wondering if the high OP was a hold over from the 1920's/30's when tolerances and processes were quite dif.
 
Some cars, my wife's 04 Sequoia, for instance, recommend a thinner oil as well, 5w30
 
That's not really true. Racing engine run with very high pressure and wouldn't if they felt it were robbing them too much over the protection gained by having it high.

Modern engines are machined to tighter tolerances and have much better control of the improved alloys and materials being used as well as better designs with roller tappets, etc. and better oil flow internally. I believe that the design allows for lower average pressure by having oil reach the needed areas much better than in the past.
 
prb51 said:
Wondering if the high OP was a hold over from the 1920's/30's when tolerances and processes were quite dif.
Click to expand...
I don't think that's necessarily the case. My '51 Chevy has the 216.5 c.i. six that has its origins in the late 1920s. Part of that heritage includes poured Babbit bearings. The oil gauge (yeah, they tended to put a full complement of gauges in cars back then) has markings something like 0 - 15 - 30! Apparently those cars didn't require very high oil pressure, either!
 
Andy, all true. But look at the size of the oil galleys in a 6 cyl Chevy engine and you can see why they easily go over 100,000 miles. The parts that move get the oil that they need in the proper volumes to support the rpms turned, so ultra high pressure is not needed.
 
Correct me if i'm wrong Andy,but seems to me the 216 cu. in.was a dipper bottom end with the rods running in a trough for oil.Only the cam and rockers were pressure feed.
Seems to me Chevy went to a pressure crank and insert bearings in 52-53 with powerglide tranny equipped models?
 
I don't recall all the details, but what I've read indicates there is a lot more to proper oil flow than just pressure and tolerances. Journal diameter and width, passage size, even the angle the passage makes with the journal can all have an effect on the required pressure.

Since it does take some power to generate the oil pressure, there has been significant focus on getting the requirement down in recent years. Same thing with the thinner oils; less energy put into pumping the oil (and pushing it out of the way of the crankshaft) means more energy available for the wheels.

BTW, the Stag motor only carries 40-50 psi of oil pressure, and factory redline was 6500 rpm. Obviously the 9 psi per 1000 rpm is only a rule of thumb, not necessarily applicable to all engines.
 
So it's the complexity/dimensions (poor design) of the oil galley that require such high pressures?
 
Andrew Mace said:
(Actually, I think the 235 c.i. came in about 1950 with the PowerGlide, and it did have insert bearings.)
Click to expand...
Along with other radical improvements, like overhead valves. But still only carried about 30 psi oil pressure; and the optional (!) oil filter was a bypass type.
 
prb51 said:
So it's the complexity/dimensions (poor design) of the oil galley that require such high pressures?
Click to expand...
Not just the galleries, but the crank journals, bearings, etc. And I'm not sure I'd call it "poor design", rather it was a chosen design spec. Something that the engine designer picked, and then verified that his design would work with that oil pressure. Higher nominal pressures probably also give extra allowance for manufacturing tolerances.
 
TR3driver said:
Andrew Mace said:
(Actually, I think the 235 c.i. came in about 1950 with the PowerGlide, and it did have insert bearings.)
Click to expand...
Along with other radical improvements, like overhead valves. But still only carried about 30 psi oil pressure; and the optional (!) oil filter was a bypass type.
Click to expand...

The 216 has overhead valves.

And the proper oil pressure is 14 PSI.
 
Paul, which racing engines? Nascar engines usually keep their oil pressure around 10 psi per 1K rpm. So usually around 75 psi max.

Our Formula Continental engines ran at 60 psi.

Smokey Yunick, long ago, found that an engine only needs 5-8 psi per thousand rpm. That oil volume was much more important than pressure...

I have a friend that still has a Double AA fueler(doesn't run it anymore as no more track on Oahu) he told me that his pressure was around 90..

Benz used to have customers complain on their cars that as the vehicle acquired miles the gauge would unpeg(usually read full pressure at about 80 psi) and wanted Benz to buy them rebuilds. Benz just put in gauges that maxed out at 50 psi..
 
Ron,
Thanks for that response.
I've had two engine builders (race prep classic cars) tell me exactly the same thing. Their rule of thumb is the same, as long as they get about 10 psi per grand (even on vehicles that originally called for much more) they run the hellout of them with no problems.
Even though they are not run as hard as they did in their 'youth' many still redline their classics and they see only normal wear on bearings, cams, etc.
I do believe our Triumphs will do just fine without pegging out the gauge.
 
Ron,

I'm showing my age. I'm going back to the 60-70's muscle car era where we jammed washers in behind the oil pump springs to bump up the OP. I was thinking of 75-80lbs back then as being high in a 442 or GTO. Don't forget, my idea of high oil pressure today is 70 lbs in my TR6!!
 
Paul,
That is high op for an American lump. What was your max rpm?
Rons ref is to cars pulling 7/8/9 thousand rpm and getting 10 lbs prssure per thou.
What I've always wondered was why you needed 70 psi @ 3500 rpm. The engine builders I talked to told me you don't.
 
PRB,

It was probably more out of watching the OP gauges and worrying about a failure, than based on scientific proof. I don't think that any engine really "needs" 70 psi at 3,500rpms, unless of course you are trying to force oil through the front of a TR6 rocker arm assembly and even then it won't happen in great volumes.

When the dealership that I worked at built a 442 for "performance", (i.e., set up for drag racing, but quietly to try to keep the warranty in affect) the clunky rocker arm pivots were replaced and generally a Crane cam went in with studs and rocker arms. Along with that came the high volume pump (read more oil pressure) because the galleys didn't get any bigger and we generally had 70-80 lbs at 6,500RPMS. Those engines really didn't like going much higher than that due to the design. I believe that the stock pump put out about 50psi at 5,500 to 6,000.

So perhaps my post was perceived as something in the really high range (like 100psi) but that was not my meaning at all. I should have prefaced it with an example.

In both of my posts above, I allude to the fact as Ron did, that volume is more important than pressure. My mistake was not defining what I thought was high.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Modern engines are machined to tighter tolerances and have much better control of the improved alloys and materials being used as well as better designs with roller tappets, etc. and better oil flow internally. I believe that the design allows for lower average pressure by having oil reach the needed areas much better than in the past.[/QUOTE]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Andy, all true. But look at the size of the oil galleys in a 6 cyl Chevy engine and you can see why they easily go over 100,000 miles. The parts that move get the oil that they need in the proper volumes to support the rpms turned, so ultra high pressure is not needed.[/QUOTE]
 
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