| [GMCnet] Oil pressures/volume. Myth/fact. And what GM required back in the 70's. [message #336428] |
Mon, 27 August 2018 14:23  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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Prior to the early 50's. Splash systems were common. Then in the late 50's. Valve spring pressures went up along with compression ratio's, and higher RPM engines. These were the main engine changes. That brought on the wide spread use of the direct pressure systems of today. GM found many decades ago. That at load. Not at idle. 25 PSI was more then adequate for the engines with compression ratios below 9.5. ( Our 403's, and455's are at 8.) At idle. 15 PSI was normal. As there was no real load on the engine. GM had the low oil pressure light come on at 7, to 10 PSI back in the 60's and 70's. These where pressures that GM felt comfortable with to protect their warranty with. When the public started to want the gauge back. And not get complaints. Oil pressure gauges displayed LOW, and HIGH. Thus avoiding numbers. Nowadays. Some engine builders address this issue by putting in high volume oil pumps in all their engine to avoid these same issues with their customers. And the customer is impressed with the fact that they have a high volume oil pump. The HV pump then covers up that the builder did. Built the engine at the outer limits of the GM specs. GM knew their engines more then ANYONE. Thus GM put in the MOST CORRECT sized oil pumps. I believe about 5.2 gallons per minute? That would serve that engine for it's entire life span. HV pumps don't lube the engine any better then the GM stock pump. They just produce more oil pressure at idle. And that's not needed. That 50% more oil they pump. Just goes directly back into the oil pan ONLY. And NOT to any of the engine moving components. The HV pump does produce 50% more heat then stock. And take 50% more horse power to run. I build engines. And would never install one on a properly built engine. The HV pump well help to extend the life of a bad engine. The 403/455 are very robust engine. Nothing hard, or special to remanufacture. They, as any engine. Require much attention to cleanliness. Not bells, and trinkets to make the build sound, or look like more then they are. Bob Dunahugh
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