Small-Block Chevy Oil Pumps - The Great Oil Pump Test
Mix A Big Batch Of Pressure, Volume, Oil Viscosity, Temperature, And Engine Power And You Have The Makings For The Great Oil Pump Test
Final engine accoutrements included a Weiand Stealth Air Strike intake and a Holley 950-cf
Oil Viscosity Test
For the second part of this lubrication lesson, we left the high-volume small-block pump in place and tried five different viscosities of oil just to see what would happen. Again, Lucas Oil supplied the slippery stuff, and the results were interesting even if they performed pretty much the way we expected. We retested the engine with a volume of 5 quarts of Lucas straight 30W petroleum-based oil to use as the standard followed by two street-oriented synthetics-20W-50 and 5W-20-and two exotic and very thin Pro Stock blends-0W-20 and 0W-10. After each test, the oil was drained from the pan and the filter. This meant a small amount of the previous test's oil remained in the filter, but we decided that it would have minimal effect on the test.
When looking strictly at power, we expected the heaviest 20W-50 weight oil to be the worst horsepower thief, so we were surprised when the straight 30W oil made the least power. This may be because it was also the only nonsynthetic tested. The chart shows that while the peak horsepower numbers changed slightly, the differences were far more apparent when we averaged the horsepower across the entire rpm band from 3,100 to 6,500 rpm. If you look only at peak or average power, it's important to note that the synthetics are clearly better than a straight weight, even with a more viscous oil like 20W-50. Comparing the 30W with the 0W-20 in terms of average power, the difference is 3.6 hp per rpm point. While that may not sound like much, with a properly tuned drag race car, it might be measureable on the dragstrip. Also notice that even though the 0W-10 outperformed the 0W-20 at the peak by 2 hp, the average was virtually a tie. Lucas says these Pro Stock race oil blends are really designed for 9,000-rpm race engines that begin to load parts pretty hard at rpm levels that our test never came close to seeing. Based strictly on horsepower, it appears from this test that a 5W-20 synthetic might be the best compromise among power, oil flow, and pressure.
It's also easy to see the differences in capacity in this photo of the two pump bodies wit
Note also how the relationship between oil flow and oil pressure remained consistent in that as pressure increased, flow decreased or as flow increased, pressure decreased. As an example, the average pressure dropped more than 11 psi between the 30W and the 0W-10, while the average flow increased from 6.1 to 7.4 gallons per minute. That's a 21 percent increase in volume between the lightweight oils and the straight 30W. In fact, all three of the lightest oils flowed dramatically more than the straight 30W. It bears emphasizing that oil flow (while more difficult to measure) is actually more important than pressure in terms of engine life. Oil flow with some pressure behind it is far superior to low oil volume with lots of pressure behind it. Perhaps the biggest surprise was that the 20W-50 synthetic performed as well as it did against the lighter oils. The biggest differential compared with the 0W-20 is in flow, where the 20W-50 lost almost 14 percent. This is understandable when accounting for oil pressure, since the 20W-50 produced the highest average at 67.4 psi compared with 0W-20's much lower 59.7. That's well over a 10 percent difference. If an average oil pressure of roughly 60 psi doesn't bother you (and it shouldn't for a small-block Chevy), then it appears the 5W-20 would be a good overall choice offering excellent flow and the very good average power with acceptable temperature.
Click here for the oil viscosity test results chart
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