Seminars on the related categories of engine oil and bearings kicked off the 23rd annual Advanced Engine Technology Conference (AETC). Held just prior to the PRI Show in Orlando, Florida, AETC brings racers, parts manufacturers and engine builders from across the country to network and discuss the latest trends in performance engines.
Scott Diehl of Driven Racing Oil opened with a clever analogy that olive oil was the first racing oil. He noted that the Romans soaked chariot axles and hubs in olive oil and also used animal fat as grease before the races.
Diehl’s presentation explained the emergence of synthetic oils in racing and how they’re developed using polyalphaolefin (PAO) base stocks. Some of the newer synthetic lubricants are also made from mPAO base stocks, which have an improved viscosity index (VI). Tests between new and used oils from the conventional mineral oil, synthetics and new-generation synthetics categories showed dramatic differences in stability and durability.
During the Q&A, Diehl stressed the importance of not mixing brands of oil.
“Every oil has different chemistry,” says Diehl. “Now you can have two chemistries trying to fight each other.”
He confirmed that mixing oils from the same brand and line, such as mixing Driven’s XP1 and XP6 is acceptable.
“Then you’re just mixing different viscosities that have the same chemistries,” adds Diehl.
Rod Sledge of King Engine Bearings expanded on the connections between bearing lubrication and clearances.
“The trend is lower viscosity oils, tighter bearing clearances and smaller journals,” says Sledge, who started off his presentation by reassuring the attendees that the recent turmoil in Israel has not affected the company’s production facility in that country. “Also, more use of synthetic oils for higher film strength and lowering of oil pressures to increase horsepower.”
Sledge says tighter oil clearances reduce peak bearing loads and provide a more even distribution of unit load over a larger area of the bearing surface.
“The oil film is also stronger because it’s spread out in a tighter area,” adds Sledge.
Matching the oil viscosity to the clearance is always “open for discussion,” but King does offer some basic recommendations. Long-duration engines such as circle track applications can utilize low clearances (.0015 – .0025) while short-duration engines need larger clearances (.0025 – .0035). A good starting point for high-performance engines is .00075-inch clearance for every inch of diameter of the journal.
For oil, King suggests only quality multi-grades formulated for racing. Oil viscosity suggestions include:
- up to .0021: 5W20
- .0021 – .0026: 5W30
- .0026 – .0031: 10W40
- .0031 – higher: 20W50
- up to .002: 5W20
- .002 – .0025: 5W30
- .0025 – .003: 10W40
- .003 – higher: 20W50
Finally, Sledge notes that a “bearing is only as good as its surroundings,” so he stressed the importance of correct housing diameter and roundness, main-housing alignments and adequate crankshaft roundness and surface finishes.