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" 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".
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.
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.
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.