SBC Oil Pressure
A common error in building a small block Chevy engine is to use too much oil pressure. As is often the case with choosing camshafts, "More’s rule" occurs. You know- "If More is better then too much is just right!"
Sure, inadequate oil pressure will starve the engine for lubrication and cause premature failure, but conversely excessive oil pressure will cause problems as well.
Oil pumps don't create pressure. It moves oil, but until there is a restriction in the system, pressure can't build.
Bearing clearance, oil viscosity, temperature and the oil pump pressure relief spring all contribute to the observed oil pressure. The oil stays under pressure until it leaves the bearings. Then it whirls around in the tornado like vortex of air around the crankshaft. As the spinning crank smacks this cloud of oil droplets, it loses energy. This energy loss is called "windage".
Modern racing oil pan design has yielded significant horsepower gains by minimizing windage.
A good wet sump system with a scraper and windage tray may pick up 20-30 hp over a stock pan.
A dry sump system can gain as much as 65 hp over a stock type pan on a racing engine.
Another hp loss is the power needed to drive the pump. No mechanical device does work for free. According to Steve Morrison of Milodon a Big Block Chevy pump (5 bolt cover) on a Small Block wastes 12 hp.
Smokey Yunick says the small Block pump(4 bolt cover) uses 10 hp at 7,000 rpm.
He also reports that some Winston Cup engines run 50 psi for qualifying just to extract every last bit of power(Circle Track April '93)
In the late seventies and eighties, Chevrolet reportedly reduced oil pressure to try to squeeze more fuel economy out of 305’s.
Other reported problems are more strain on the drive system, and the speculation that mechanical pulses through the distributor drive increase spark "scatter". (see Melling Link below for comments on this)
I've seen stock oil pump drive shafts fatigue and break from the increased load caused by a HV/HP pump. Look at your stock shaft and imagine it having to endure a 10-12 hp load for 100,000 miles.
How much is enough? The rule of thumb: "10 psi for every 1,000 rpm", was originated more than 25 years ago by Smokey Yunick. Does that mean that because you think your engine will run 7,000 rpm you need 70 psi?
No. Recommendations also depend on application.
Note: All pressures are "hot" (ideal temp is about 220 F)
Street engines 35-45 psi
Street HP 45-55 psi
Racing (only) 60 psi
Pro, turbocharged 70+ psi
In the 1984 Power Manual, Chevrolet recommends 65 – 80 psi for racing applications. This means purpose built, trailered racecars. Bob Mainetti of Canton Racing was quoted in Circle Track (April ’96) as saying: " At 6,500, you want 50 to 60 pounds. At 7,500, 60 pounds is plenty of pressure."
What was thought true in the last century is changing in this one. Gary Penn from GM's Performance Parts division says (CT June '03) "At GM we are big fans of synthetic oil motor oil after break-in. The stuff has really improved over the years and allows you to get by with things you never thought possible." He goes on to say: "...We run only 3 qts of 0W-10 in the motor.... and run it with no oil pressure across the finish line at 7,500 rpm" Gary concludes with: "The advanced quality of the (synthetic) oils on the market means the old rule of thumb that you need 10 pounds of oil pressure per 1,000 rpm is not valid anymore."
Setting SBC oil pressure
Changing the oil pressure relief spring in the pump will adjust the maximum oil pressure. This requires removing the pump cover and carefully driving out the roll pin. Replace the spring, cup and roll pin exactly as removed. Spring pressure ratings are nominal hot pressures. If your bearing clearances are too loose, then your actual pressure will be lower. If you run a thicker viscosity oil then your pressures may be higher, especially when cold.
Most aftermarket high-pressure pumps you buy come with the Z-28 spring (#3848911) that produces 65-70 psi. This is too high for most engines. Not surprisingly, these pumps often come with a lower pressure spring in the box!
I’ve found that the best High Performance oil spring for sbc engines is the factory Corvette L-82 relief spring. The part number is: #10044435
This spring yields about 50-55 psi and is the same spring used in the high performance ZZ4 crate engine.
Cost is about $1 from the dealer and has to be the all time bargain factory HiPo part. While you're there, buy a magnetic drain plug under PN 23011420. This will trap metallic particles generated by normal wear and tear. Clean it off every oil change.