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Old 05-05-2010, 08:10 AM
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What should oil pressure be on semi-fresh SBC350?

What should the oil pressure be on a SBC 350?

I didn't have a gauge during cam break-in (I know, this was dumb).

After changing oil and filter last night after the break-in from Saturday, I installed an oil pressure gauge right behind the distributor.

After startup, it pumped up to about 35 psi and stayed there for our 10 minute ride that included periods of hard acceleration. Should it fluctuate with acceleration and/or idle or is a constant pressure normal?

A little background. It was purchased from a guy that had it in a street rod and said it wasn't fast enough for him so it only had a few hundred miles on it. A friend that has built several motors looked at the crank and cam bearings, cylinders, etc. and agreed. We replaced the heads after having a valve job and checking for cracks (smogger 882's), new cam, lifters and pushrods, salvaged Performer RPM manifold and new Holley 670 Street Avenger carb. Has the dish pistons with valve reliefs so I used the fel-pro 1094 0.015 head gaskets to get the squish down since the pistons were down in the block about 0.025. Compression is only probably about 8.25 to maybe 8.5:1

As always, I appreciate the help.

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Old 05-05-2010, 09:59 AM
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35 lbs sounds a bit low. It also depends on the oil pump your using. On my 289 Ford for example, at start up, I have 80 lbs of oil pressure. As the oil gets hot and thins, the pressure will fluctuate and be lower than start up. At idle, the oil pressure can actually drop to 10-20 lbs of pressure. As soon as you apply the pedal, it should jump up to a good range between 40-60 lbs of pressure.
Sometimes, oil filters can effect pressure, try changing to another brand and see if that makes a difference. You may want to check your pressure using another pressure gauge. Just because it's a gauge or its new, doesn't mean it works right...
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Old 05-05-2010, 10:20 AM
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35 psi is within an acceptable range for a SBC.
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Old 05-05-2010, 06:08 PM
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35 is "ok" for a SBC that isn't going to see sustained high RPM. I would expect some fluctuation though, have you tried a different gauge? I got a real nice Mellings oil pump with only a couple hours on it for free because a guys new 355 only showed 20 PSI so he immediately replaced the new oil pump with a super trick, high volume, high pressure, high dollar pump and gave me the old one for a "leftovers" motor I was putting together. Pressure was till only 20 PSI. A friend finally convinced him to try a different gauge. It jumped to 65.

My kid had a F150 4X4 with 460 that was only showing about 35 PSI, he used Fram oil filters and finally had one fail right after an oil change. He only lost a couple Qts. before he shut it down, fortunately it had a 10 Qt. Milodon pan. I told him to get a Bosch filter and he replaced the lost oil. It immediately showed 10 more Lbs. of oil pressure just by switching filters. He hasn't used a Fram filter since.
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Old 05-05-2010, 07:10 PM
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That pressure of 35lbs sounds low. At startup on my smallblock I have 80lbs. After warmup usually between 50-60lbs. 35lbs the motor should still be fine in my opinion.
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Old 05-05-2010, 07:39 PM
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Quote:
Originally Posted by 075turbo
What should the oil pressure be on a SBC 350?

I didn't have a gauge during cam break-in (I know, this was dumb).

After changing oil and filter last night after the break-in from Saturday, I installed an oil pressure gauge right behind the distributor.

After startup, it pumped up to about 35 psi and stayed there for our 10 minute ride that included periods of hard acceleration. Should it fluctuate with acceleration and/or idle or is a constant pressure normal?

A little background. It was purchased from a guy that had it in a street rod and said it wasn't fast enough for him so it only had a few hundred miles on it. A friend that has built several motors looked at the crank and cam bearings, cylinders, etc. and agreed. We replaced the heads after having a valve job and checking for cracks (smogger 882's), new cam, lifters and pushrods, salvaged Performer RPM manifold and new Holley 670 Street Avenger carb. Has the dish pistons with valve reliefs so I used the fel-pro 1094 0.015 head gaskets to get the squish down since the pistons were down in the block about 0.025. Compression is only probably about 8.25 to maybe 8.5:1

As always, I appreciate the help.
Unless your oil has the weight of water, even a stock Chevy oil pump should take cold idle oil pressure to the relief valve pop off which is 50-60 psi for regular production engines and 60-70 for production performance engines. This should drop to 25-35 psi at idle when the sump gets up to about coolant temp, that usually takes 10-15 minutes without a coolant warmed to oil heat exchanger. It should, with hot oil, still hit 50-60 for a production pump and 60-70 for a production performance pump as used in the 302 and original LT1 by 2 maybe 3 thousand RPM.

I'd suspect the gauge, or if electric the sender or system voltage to the sender, before I peel parts off the engine. Of course the other reasons for low oil pressure are to be found internally from excessive leakage on the pressure side from wide bearing clearances; or leaking galley plugs; or the distributor not installed correctly to where it opens the right side lifter galley to the sump. The other side of the coin on the pickup would be too much or too little distance between the pickup and pan allowing air to be sucked in with the oil, or the pickup so close to the pan bottom it can't feed; or the pickup tube leaking air at the pressed fit to the pump. Last would be with the relief valve itself having a weak control spring or the valve stuck open in the bypass configuration. And there's other things but these are the ones you usually find.

Too bad about the pistons, chambers and compression, or rather lack there of. This is a long way from an efficient and effective set up that's costing power not developed for the excessive fuel burned.

Bogie
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Old 05-05-2010, 07:50 PM
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35 does sound low,

On my 80 camaro, I have an oil pressure guage, and at start up, it is somewhere in the 80 range pressure, then at idle, 60. If I rev the engine, it does get higher also.
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Old 01-13-2013, 09:45 PM
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Was the old rule of thumb 10 psi for every 1000 rpm plus 15 for idle?
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Old 01-13-2013, 09:55 PM
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It also depends on the viscosity of the oil thats in your engine.
Over 20 pounds at idle when warm is ok. The pressure should go up with rpm.double check the guage.You can buy heavier oil if the pressure is low.
Synthetic oil reads lower in most cars
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Old 01-13-2013, 10:02 PM
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This orig. post is going on 3 yrs old kids.........
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