I ran Kendall 40wt racing oil for years in my 340. 30,000 miles and 30 years and the bearings still looked like I just took them out of the box. I built the motor in 1977 and sold the car in 2008, I went though it a couple years before I sold it. Basically I had to rebuild the clutch and have the flywheel reground so I went through the motor, to my amazement the bearings still looked new, Clevite Micro. I had the motor apart at least 8 times in the 30 years just to look at it. I raced it for about ten years on and off, never easy on it 7600RPM shift points and through the traps at about the same rpm. When changing the oil hot it was still thick, probably took more power to push the thick oil than the thin stuff but I swear by it.
