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Old 04-13-2004, 12:36 PM
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Sbc Oil Pressure - How Much Is 2 Much?

I have a 350 bored .040", mellings high volume pump. When Cold, if revved a little near 2500rpm-3000rpm, oil pressure gets to 90psi. When hot, maximum at full throttle is around 78 psi. Guage used to check this is an Autometer.

Is this too much? Can it cause damage to anything?

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Old 04-13-2004, 12:40 PM
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That is way more peressure than any street/strip engine needs. At speed I guess it could pump all you oil into the valve covers, will wear out the pump shaft a little quicker and definietly uses a little more HP. 40 psi would be plenty.
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Old 04-13-2004, 12:45 PM
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Thats what I thought, the maximum from what i've read being 65psi as heaps and probably the top pressure allowable. My engine has covered about 2500 miles since rebuilt, so its still fresh I spose. My engine builder laughed when I told him, and said that by rule of thumb, I have enough for x amount of horsepower and so forth when figured out, but whouldn't cause any hassles.

I always thought it could blow out seals and gaskets if too high. Could that be a possibility?
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Old 04-13-2004, 01:14 PM
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I run a liitle as possible. I have to rebuild more often as well. I always liked 10 pounds per 100 horse rule. That theory doesn't always apply though. With older cross drilled crank's you needed a lot of pressure to help overcome cetrifgul forces to feed the mian's. With newer crank's the oil galleys are drilled from the mians and it's less affected by the swinging of the rod ends. I wouldn't worry about idle pressure either as long as it comes to 30 pounds at 2000 RPM.

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Old 04-13-2004, 01:34 PM
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My idle pressure @ 850rpm hot is around about 25-30psi. What sort of other damage could excessive oil pressure cause? I was told by some that if there's lots of oil in the top end of the engine, then there's problems with lubrication down low.
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Old 04-13-2004, 01:46 PM
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Try changing to a different brand of filter. Maybe the GM duraguard PF1218. Might make a difference if the current one is messed up.

Mark
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Old 04-13-2004, 01:51 PM
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I did try different filters, but without luck Mark. The pressure didn't change not one bit. I am using a short filter for header clearance though, so I might get a remote filter mounting kit, and mount a long style filter to see what happens.

Thanks to everyone for your help, really appreciate it
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Old 04-13-2004, 01:59 PM
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In 1991 I used to have a vega with a 350chevy built for street strip, I bought the car already built and it also had the same P.S.I as yours. I kept the car for about 2 years and never had any problems with it running that kind of oil pressure.
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Old 04-13-2004, 01:59 PM
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I'm curious, what is a "Holden Coupe"? It looks like an early '70s Chevy Monte Carlo. Am I close? LOL
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Old 04-13-2004, 02:10 PM
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Actually, I thought the same recently when I saw a Monte Carlo Pic. I think my Monaro Coupe is a little smaller in total size. In 1974 and on, no Australian car came out with a Chevy powerplant. The engines were Australian built Holden 5.0L in largest size (308 C.I.), but I have a small block for mine, as they can fit staright in wiothout hassle, and they were in the previous model Monaros as an option. Back in the day, we had an American Designer Down Under, so he probably used GM USA styling cues. When compared to a Trans Am, interior wise, it looks similar in terms of the steering column, and seating feel. The rear has a spolier which reminds me of the Trans Am, or Camaro models. Its fascinating as to what vehicle is similar in Australia to what vehicle in the US. We seem to have a strong partnership with Pontiac if anything. I recently had the steering column rebuilt in my Monaro, and the Lock and Barrel and Keys cam from the US. Incidently, my Monaro is yellow, but looks the same as my avatar. I just couldn't get the pictures scanned.

Thanks for the security on that one Brainsboy. maybe I haven't got much to worry about. At least I have an abudance of pressure, lol, better than no pressure.
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Old 04-13-2004, 03:15 PM
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I'm not familiar with the Melling pump but normally all you need to do is change the relief spring to adjust pressure. Cost is low - a new spring and a new pan gasket.
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Old 04-13-2004, 03:28 PM
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Actually thats definately the wiser thing to do Willys36, and i'll be doing that when the motor comes out of my car to be put into my Monaro. At least I'll have piece of mind that way
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Old 04-13-2004, 05:23 PM
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The stock 5.3L in my 04 z71 runs 80psi 3/4 throttle.
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Old 04-13-2004, 05:25 PM
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I would change the spring like Willys talked about.With the numbers you describe I would say your clearances are good and you have a good oil pump for you application.The high pressure at high speed is a bit tough on the distributor gear and might make the oil run hotter,so I would run a softer relief spring so that you can bypass more oil at high speeds without loosing that nice and healthy low speed pressure.
I tried shimming the heck out of an oil pump spring once{I read the Grumpy Jenkins book like everybody else},and with 3 brass flat washers in the spring pocket I had enough oil pressure to blow the gasket off the oil filter every time I cracked the throttle.I could blow the entire contents of my 8 quart extra deep pan all over the shop floor any time I wanted.I replaced spring and had no more problems.Now that was too much oil pressure!

BTW,the only reason I shimmed the pump like the Grump was because I had read another S&A book that told me to run loose clearances and that caused me to have 10psi of hot idle pressure,so I thought the spring trick would help.It didnt help the hot idle pressure,but it made a mess out of the cold start high speed pressure.Sometimes reading too much is a dangerous problem.
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Old 04-13-2004, 06:59 PM
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I dont know if someone mentioned this already but I was always told for every 1000 rpm you need 10 more psi 7000 rpm 70 psi, if you have problems filling the valve covers with oil you can get restricted push rods which will solve that problem.
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