When Shell Oil CO. bought Pennzoil they change the formula to make it better with some different additives, a friend of mine who crew chiefs a winning SCCA spec. car told me about it around 15 yrs ago.
Valvoline now has the exact same feel when rubbing it between my fingers and probably the exact same additives as Pennzoil used to make their race oil slicker with less resistance work Valvoline VR oil is a lot easier for me to buy than Pennzoil racing oil also.
I have seen power gain by running hotter oils or thinner oils, hence using the 10W30Wt now versus the 20W50 WT oils up
If Valvoline or Pennzoil offered a 5W10 racing oil I would use it up
I use 5W20 WT Valvoline in all of my hot street motors with zinc additives, if needed for the cam and lifters. Same weight oil on street roller cam motors with no additives thumbs
I'm not completely sold on synthetic oils yet, maybe some day confused

Last edited by Cab_Burge; 02/14/18 05:34 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)