I have been using 5W20Wt Valvoline non synthetic in all my Hi Po Mopar motors for a long time, the roller lifter motors get no additives, the flat lifter cam motors get a bottle of either zinc additive or Comp Cams lcam lube There have been horror storys posted on this site about deisel oil foaming, I have no expereince with that so I won't comment on it You need to think about what oil does for our motors, it needs to lubricate and cool That being said thinner oil moves quicker and with less resistance to the oil pump when cold, it also take less HP to turn the oil pump I've seen 10 HP loss at 130 F with straight 30 Wt oil years ago compared to the same oil and motor when we let the oil temps climb to 160 F No loss or gain of HP or torque when using 5W20Wt from 80F to 230 F I do run very loose oil clearances on the rod and main bearings also, .003 + on both I've shifted my 650 HP + pump gas street motor at or above 7000 RPM for a long time when running it at the track, a lot of laps over the years with no noticeable bearing wear or abuse OP, run what you feel comfortable with BTW, I do run both Rotella and Delo 400 in my CTD truck, depending on where and when I have the oil and filter changed and what they have in stock If you want to run race oil in your motor the only one I would run now is the RACING Pennzoil 25W50WT It has some lube additives, friction reduction, that no other oil has that I know of You can feel it when rubbing it between your fingers All the SCCA raers I know use it now