I have seen 10 hp differences on a DTS engine in using 30 WT oil at 130 F oil temps versus warmng the oil up to 170F. I started using 5w30 and 5W20 wt. oil and now see no differences in HP gains at 100F and 190F oil temps I have been told by NHRA stock class racers that 5W20 synthetics are worth a .1 to .18 in ET depending on the old oil that they used before switching I do know some Comp Eliminator racers that use 0 Wt synthetic oils that change the oil after every round because the oil is worth .003 ET gain and the motor will blow up if you run it twice at WOT, these are high RPM N/A motors that make 2.25 and up HP per C.I. , That is insane to me but I don't use it.