At high rpm, the reliability of any internal combustion engine depends on a consistent and high-quality oil supply. This is especially true of supercharged engines. In blown-alcohol and blown-fuel applications, the load on the oil film in main and rod bearings is extreme. To perform well under those loads requires high oil volume and minimal degradation of that oil volume by pump cavitation.
 

"Cavitation" is the emergence of cavities, or bubbles, in the oil which can develop in low pressure areas near the inlet of an engine oil pump. At the outlet of the pump, higher pressure causes some of those bubbles to rapidly collapse?actually it's more like a violent "implosion". These implosions cause shockwaves to travel through the liquid and impact internal parts potentially causing damage to the pump. The rest of the air bubbles mix with the oil making an oil foam which is a very poor lubricant. Once the pump output is oil foam, bearing reliability plummets and the possibility of internal engine failure increases exponentially.
 

Recently, Bill Miller Engineering tested several engine oil pumps popular with blown-alcohol and blown-fuel racers. The BME oil pump test stand drives the pump at engine speed. During these tests, BME measured the rpm of the pump, inlet vacuum, flow through the pump and outlet pressure. The results can be viewed in the short video below.

It's obvious from the testing that, when pumping high-viscosity oil, it is extremely important for the pump inlet and the hose which feeds it be absolutely as large in inside diameter as possible. For example, the oil pump on the BME Top Fuel Dragster has an AN-20 inlet which has been increased in inside diameter from 1.08-to-1.20-in, a 23.5% increase in area. That larger cross-sectional area makes it easer for atmospheric pressure to push oil to the pump inlet and minimizes cavitation.